UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Mechanisms of liquid-phase sintering in Fe-Cu mixtures Magee, Brian Eric 1975

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1975_A7 M33_4.pdf [ 11.38MB ]
Metadata
JSON: 831-1.0078694.json
JSON-LD: 831-1.0078694-ld.json
RDF/XML (Pretty): 831-1.0078694-rdf.xml
RDF/JSON: 831-1.0078694-rdf.json
Turtle: 831-1.0078694-turtle.txt
N-Triples: 831-1.0078694-rdf-ntriples.txt
Original Record: 831-1.0078694-source.json
Full Text
831-1.0078694-fulltext.txt
Citation
831-1.0078694.ris

Full Text

MECHANISMS OF LIQUID-PHASE SINTERING IN FE-CU MIXTURES by  BRIAN .A.Sc.  (Honours),  A THESIS THE  ERIC  Queens  SUBMITTED  University  IN  REQUIREMENTS MASTER  in  MAGEE  PARTIAL FOR THE  OF A P P L I E D  the  at  Kingston,  FULFILMENT DEGREE  OF  OF  SCIENCE  Department of  METALLURGY  We a c c e p t requ i red  THE  this  thesis  as  conforming  to  standard  UNIVERSITY  OF  BRITISH  January,  1975  COLUMBIA  the  1973  In p r e s e n t i n g t h i s  thesis  an advanced degree at the L i b r a r y s h a l l I  in p a r t i a l  fulfilment of  the U n i v e r s i t y of B r i t i s h  make i t  freely available  f u r t h e r agree t h a t permission  for  the requirements f o r  Columbia,  I agree  r e f e r e n c e and  f o r e x t e n s i v e copying o f  this  that  study. thesis  f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s of  this  representatives. thesis  It  is understood that copying o r p u b l i c a t i o n  f o r f i n a n c i a l gain s h a l l  written permission.  Department of  ffigfe  U'lJjtf)  The U n i v e r s i t y o f B r i t i s h Vancouver 8, Canada  Date  JfiA  JS  l 1l^ C  Columbia  not be allowed without my  ABSTRACT  Continuous  d i l a t o m e t r y and m e t a l l o g r a p h i c t e c h n i q u e s  have been used t o study the..dimensional changes which  occur  when i r o n - c o p p e r compacts a r e s i n t e r e d above t h e m e l t i n g p o i n t o f copper.  Among the v a r i a b l e s i n v e s t i g a t e d were:  a) the e f f e c t o f s o l i d - s t a t e p r e s i n t e r i n g t h e compacts, b) copper c o n t e n t , c) p a r t i c l e s i z e , ' d ) i n i t i a l compact d e n s i t y and e) t h e h e a t i n g r a t e through the m e l t i n g  temperature.  F i v e d i f f e r e n t p r o c e s s e s c a u s i n g d i m e n s i o n a l change were i d e n t i f i e d . secutively:  Three c o n t r a c t i o n p r o c e s s e s o p e r a t e d  1) rearrangement,  3) c o a l e s c e n c e . w i t h processes  Two  con-  2) s o l u t i o n - p r e c i p i t a t i o n  and  expansion processes operated simultaneously  (1) and  ( 2 ) , they were:  4) e x p a n s i o n due  to  d i f f u s i o n o f copper i n t o i r o n and, 5) e x p a n s i o n r e s u l t i n g the p e n e t r a t i o n o f y - i r o n g r a i n b o u n d a r i e s by copper In  from  liquid.  t h e e a r l y s t a g e s o f s i n t e r i n g the i r o n was  in a  ' d i s p e r s e d ' s t a t e , w h i l e i n the l a s t s t a g e i t e x i s t e d as a s o l i d network.  That change i s a t t r i b u t e d t o an i n c r e a s e i n  t h e v a l u e s o f the d i h e d r a l and w e t t i n g a n g l e s l i q u i d - s o l i d system d u r i n g s i n t e r i n g .  (<j> and 8) o f t h e  I t i s suggested  that  i n i t i a l l y h i g h c o n c e n t r a t i o n s o f oxygen a t the s o l i d - l i q u i d  i n t e r f a c e s causes a low v a l u e o f y  CT  and t h u s , t h e v a l u e s o f <j>  and 6 a r e i n i t i a l l y low. As t h e oxygen c o n c e n t r a t i o n a t t h o s e i n t e r f a c e s decreases w i t h t i m e , <j> and 9 become p o s i t i v e , p e r m i t t i n g coalescence t o occur. D i f f e r e n c e s among t h e r e s u l t s o f p r e v i o u s  investiga-  t i o n s i n t h e Fe-Cu system have been e x p l a i n e d by a t t r i b u t i n g them t o d i f f e r e n c e s i n t h e t h e r m a l h i s t o r i e s o f compacts. I t i s suggested  t h a t some a d d i t i o n s t o t h e Fe-Cu system,  w h i c h reduce e x p a n s i o n d u r i n g l i q u i d - p h a s e s i n t e r i n g , do so by a c t i n g as i n t e r n a l d e - o x i d a n t s and p r e v e n t i n g a z e r o d i h e d r a l angle from b e i n g a t t a i n e d .  TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  viii  LIST OF FIGURES  x  ACKNOWLEDGEMENTS  xv  Chapter 1  INTRODUCTION .  1  1.1  Practical Significance of LiquidPhase S i n t e r i n g  1.2  Iron-Copper Phase E q u i l i b r i a  1.3  Role o f Surface Energies i n L i q u i d Phase S i n t e r i n g  6  . ..<:  1.3.1 C o n t a c t and D i h e d r a l Angles  6  1.3.2  1.3.3  1 3  Factors Affecting the C o n t a c t and D i h e d r a l Angles  10  W e t t i n g i n t h e Fe-Cu System  1.4  Mechanisms o f L i q u i d - P h a s e S i n t e r i n g  12 . .  14  1.4.1  Rearrangement. . .  14  1.4.2  Solution-Precipitation Theories Coalescence  15 IS  1.4.3  iv  Chapter  Page 1.5  P r e v i o u s S t u d i e s o f t h e Fe-Cu System  1.6 2  1.5.1  E a r l i e s t Observation  19  1.5.2  Practical Investigations. . . . .  19  1.5.3  Dilatometer Studies  22  1.5.4  Other S t u d i e s  27  1.5.5  Expansion E f f e c t s  27  1.5.6  Shortcomings o f P r e v i o u s Work . .  30  O b j e c t i v e s o f T h i s Work  MATERIALS, APPARATUS AND EXPERIMENTAL PROCEDURE 2.1 M e t a l Powders and Specimen  2.2  3  19  32 34  Preparation.  34  The D i l a t o m e t e r  42  2.2.1 2.2.2  42  Description Advantages o f t h e D i l a t o m e t e r Design  4 6  2.3  D i l a t o m e t r i c Technique  47  2.4  Other E x p e r i m e n t a l P r o c e d u r e s  53  OBSERVATIONS AND RESULTS 3.1  3.2 3.3  Observations: and C l e a n i n g  5 7  B l e n d i n g , Compacting 5 7  3.1.1  B l e n d i n g and Compacting . . . . .  57  3.1.2  Cleaning  60  Changes i n Weight and Dimensions During Dilatometry  66  D i l a t o m e t r i c Data f o r a Pure I r o n 71 Compact v  Chapter  Page 3.4  S i n t e r i n g B e h a v i o u r o f Fe-22 Cu-Mixtures 3.4.1 3.4.2  73  Dilatometer P l o t f o r PCM-2-20  73  S o l i d State Dimensional Changes  74  3.4.3  The Onset o f M e l t i n g  79  3.4.4  Temperature G r a d i e n t s i n the D i l a t o m e t e r Specimens . . . . M i c r o s t r u c t u r a l Changes Coincident with Melting  88  S t r u c t u r a l Changes i n Stages I I I , IV and V .  90  3.4.5 3.4.6 3.4.7  Summary o f M e t a l l o g r a p h i c Observations  87  107  3.5  Proposed Mechanisms o f S i n t e r i n g i n Fe-22Cu M i x t u r e s  109  3.6  Effect.of Sintering Variables  120  3.6.1  General  . . . . .  120  3.6.2  E f f e c t o f P a r t i c l e S i z e and P a r t i c l e Size D i s t r i b u t i o n . . . .  122  3.6.3  E f f e c t of P r e s i n t e r i n g  128  3.6.4  E f f e c t o f H e a t i n g Rate and H o l d i n g Temperature  137  3.6.5  E f f e c t of I n i t i a l Density . . . .  143  3.6.7  E f f e c t o f a D i f f e r e n t Type of I r o n Powder Use o f P r e a l l o y e d Powder. . . . .  149 152  3.6.8  vi  Chapter 4  Page COMPARISON WITH PREVIOUS WORK 4.1 4.2 4.3 4.4  5  155  Comparison w i t h t h e R e s u l t s of Kingery  155  Comparison w i t h B o c k s t i e g e l s Work  162  Comparison w i t h Other P r e v i o u s Work  163  G r a i n Boundary P e n e t r a t i o n and the D i h e d r a l Angle  164  1  CONCLUSION  168  5.1  Summary  168  5.2  F u t u r e Work  1 7 2  REFERENCES  1 7 3  vii  LIST OF TABLES Table I  II III IV V VI  Page R e s u l t s o f P r e v i o u s S u r f a c e Energy, C o n t a c t and D i h e d r a l A n g l e Measurements i n t h e Fe-Cu System  13  M e t a l Powders  35  C o m p o s i t i o n o f M e t a l Powders  36  Powder S i z e F r a c t i o n s  3 7  Powder M i x t u r e s Used i n Compacts  38  S i z e F r a c t i o n s o f Powders i n Specimen PCM-UF-2  VII  . .  D i s p o s i t i o n o f Samples  VIII  IX X XI  54  Average D e n s i t y o f F e - 2 2 C u ^ l l Carbowax Compacts P r e s s e d a t 60 k . s . i . .  XII  40  .  59  Compacting and C l e a n i n g  61  Weight Loss D u r i n g C l e a n i n g . .  65  T o t a l Change i n Dimensions and Weight During Dilatometry Runs w h i c h were R e p r o d u c t i o n s o f t h e E a r l y Stages o f Run PCM-2-20  68  viii  75  Table XIII XIV  /XV  /XVI-  . XVII, XVIII XIX  Page Runs Showing E f f e c t s o f V a r i a b l e s on L i q u i d - P h a s e S i n t e r i n g Mechanisms  121  E f f e c t o f P a r t i c l e S i z e and P a r t i c l e S i z e D i s t r i b u t i o n on t h e D i m e n s i o n a l Changes o f Compacts D u r i n g L i q u i d - P h a s e S i n t e r i n g  127  E f f e c t o f P r e s i n t e r i n g on t h e D i m e n s i o n a l Changes o f Compacts D u r i n g L i q u i d - P h a s e Sintering. . . • E f f e c t o f H e a t i n g Rate and H o l d i n g Temperature on D i m e n s i o n a l Changes D u r i n g L i q u i d - P h a s e Sintering.  1 3 4  1 4 0  E f f e c t o f * n i j t i : a l c D e n s i t y on D i m e n s i o n a l Changes D u r i n g L i q u i d - P h a s e S i n t e r i n g  145  E f f e c t o f Copper C o n t e n t on D i m e n s i o n a l Changes D u r i n g L i q u i d - P h a s e S i n t e r i n g  148  E f f e c t o f Powder Type on D i m e n s i o n a l Changes During Liquid-Phase S i n t e r i n g  150  ix  LIST OF FIGURES Figure  Page  1  Fe-Cu phase diagram . . . . . . .  4  2  The c o n t a c t a n g l e ,  7  3  The d i h e d r a l a n g l e ,  6 <j> . . .  9  4  S p h e r i c a l p a r t i c l e s h e l d t o g e t h e r by r-.^-p c a p i l l a r y p r e s s u r e o f t h e l i q u i d phase 5  6  7 a. 8  M i c r o s t r u c t u r e o f a 75/25 Fe-Cu compact, s i n t e r e d a t 1120°C f o r an u n s p e c i f i e d time from Chadwick et al. [ 2 1 ] , 500x Log f r a c t i o n a l d e n s i f i c a t i o n v s . l o g t i m e , f o r Fe-Cu compacts c o n t a i n i n g 11.3, 22.0 and 43 w e i g h t p e r c e n t copper a t 1150°C, from K i n g e r y [14] The e f f e c t o f copper c o n t e n t on t h e s i n t e r i n g b e h a v i o u r o f Fe-Cu compacts o f <150u powders a t 1150°C, from B o c k s t i e g e l [ 1 5 ] . . . . . . . m  The e f f e c t o f powder s i z e on t h e s i n t e r i n g b e h a v i o u r o f Fe-»7.u5eG,upeompaef s f I f rom per -. B o c k s t i e g e l [15] m  9  11  21  .  .  23  25  25  Heating cycle f o r cleaning  41  10  D r i l l e d compact  43  11  The d i l a t o m e t e r  44  x  Figure  Page  12  'Normal' h e a t i n g  13  'Rapid' h e a t i n g  14  'Slow' h e a t i n g  15  ' P r e s i n t e r i n g ' heating  16  S e c t i o n o f compact.PCM-2£14 a f t e r c l e a n i n g .  17  D i l a t o m e t e r p l o t f o r PM-2; a pure i r o n specimen h e a t e d w i t h a normal c y c l e  72  D i l a t o m e t e r c u r v e f o r PCM-2-20, showing s t a g e s o f d i m e n s i o n a l changes . . . .  76  19  E a r l y s t a g e s o f Run PCM-2-20, showing where samples i n T a b l e X I I were stopped  77  20  A s e c t i o n o f sample PCM-2-12 a t lOOx  80  21  S e c t i o n o f compacts used f o r m e t a l l o g r a p h y . . . .  80  22  A s e c t i o n o f sample PCM-2-6 a t 300x  81  23  A s e c t i o n i n sample PCM-2-21 a t 300x,  18  cycle  49  cycle  50  cycle  51 cycle  52 ...  58  t a k e n a t l o c a t i o n 'B'  81  24  Macrophoto o f PCM-2-5 a t 5x  83  25  A s e c t i o n i n sample PCM-2-5 a t 300x* t a k e n a t p o s i t i o n 'A' A s e c t i o n i n sample PCM-2-5 a t 300x, t a k e n a t p o s i t i o n 'B'  83  26 27  A s e c t i o n i n sample PCM-2-5 a t 300x, t a k e n a t l o c a t i o n 'C'  xi  84 84  Figure 28 29 30 31  Page A s e c t i o n i n specimen PCM-2-5 a t 300x, t a k e n a t p o s i t i o n 'D' A s e c t i o n i n specimen PCM-2-5 a t lOOx, taken a t l o c a t i o n ' C . A s e c t i o n i n specimen PCM-2-5 a t lOOx, t a k e n a t l o c a t i o n 'D'  85 85 86  A s e c t i o n i n specimen PCM-2-5 a t lOOx, t a k e n a t l o c a t i o n 'B' . . . . . . .  86  32  A s e c t i o n i n specimen PCM-2-5 a t 1200x  89  33  A s e c t i o n i n sample PCM-2-18, 1200x  91  34  A s e c t i o n i n PCM-2-18, 1200x  93  35  A s e c t i o n i n PCM-2-17, 1200x  93  36  A s e c t i o n i n PCM-2-17, 600x  94  37  A s e c t i o n i n PCM-2-17, 3 00x  94  38  A s e c t i o n i n PCM-2-22, 1200x  95  39  A s e c t i o n i n PCM-2-22, 300x  97  40  A s e c t i o n i n PCM-2-20, 300x  99  41  A s e c t i o n i n PCM-2-20, 600x  99  42  A s e c t i o n i n PCM-2-6, lOOx  100  43  A s e c t i o n i n PCM-2-18, lOOx  102  44 45  A s e c t i o n i n PCM-2-22 (Area #1) , lOOx A s e c t i o n i n PCM-2-22 (Area #2) , lOOx  102 103  xii  Figure  Page  46  A s e c t i o n i n PCM-2-20, 10 Ox  103  47  S u r f a c e o f PCM-2-18 a t 2000x, viewed through a scanning e l e c t r o n microscope  105  S u r f a c e o f PCM-2-20 a t 1040x, as viewed w i t h a scanning e l e c t r o n microscope  105  Absorbed e l e c t r o n image o f a s e c t i o n i n PCM-2-20; lOOOx . .  106  48 49 50  Copper X-ray image o f a s e c t i o n i n PCM-2-20-; lOOOx  106  51  D i l a t o m e t e r p l o t f o r Run PCM-2-20  110  52  D i l a t o m e t e r p l o t f o r Run PCM-A.  124  53  D i l a t o m e t e r p l o t f o r Run PCM-5-6  125  54  D i l a t o m e t e r p l o t f o r Run PCM-6  126  55  D i l a t o m e t e r p l o t f o r Run PCM-UF-2  129  56 57  D i l a t o m e t e r p l o t f o r Run PCM-5-12 . 130 D i l a t o m e t e r p l o t f o r Run PCM-5-13 . . . . . . . . 131  58  D i l a t o m e t e r p l o t f o r Run PCM-2-10 ( s p u r i o u s data)  132  59  D i l a t o m e t e r p l o t f o r Run PCM-2-19  133  60  D i l a t o m e t e r p l o t f o r Run PCM-2-23  138  61  D i l a t o m e t e r p l o t f o r Run PCM-2-24  139  62 63  D i l a t o m e t e r p l o t f o r Run PCM-2-25 D i l a t o m e t e r p l o t f o r Run PCM-2-30  142 144  xiii  Figure  Page  64  D i l a t o m e t e r p l o t f o r Run PCM-2-100  147  65  D i l a t o m e t e r p l o t f o r Run ATOCM-5  151  66  D i l a t o m e t e r p l o t f o r Run PA-2-1  67  Log f r a c t i o n a l change i n l e n g t h o f compacts ( r e l a t i v e t o L Q J the length a t melting)  153  M  versus  ( t - t ^ ) , t h e time from m e l t i n g , d u r i n g  Stage I I I s h r i n k a g e  156  68  D i l a t o m e t e r curve f o r Run PCM-5-6 . . . . . . . .  69  f r a ct t ihoen same a l d e dn astiaf i cc oa rt ri eo cn t e d vK is n. g esriyn'tse r di an tg a ,t i mfeo, r and t o e l i m i n a t e t h e e f f e c t o f Stage IV e x p a n s i o n . .  160  R e s u l t s o f d i h e d r a l a n g l e measurements i n t h e Fe-Cu system, from Berner et al. [12] . . . .  165  70 71  xiv  158  ACKNOWLEDGEMENTS  The a u t h o r w i s h e s t o thank h i s s u p e r v i s o r , Dr. J.A. Lund o f t h e M e t a l l u r g y Department, f o r h i s c o n t i n u i n g encouragement and a d v i c e d u r i n g a l l s t a g e s o f t h e work. u n d e r t a k i n g an e n j o y a b l e and r e w a r d i n g Thanks a r e a l s o due t o :  I t made t h e  experience.  B.N. W a l k e r , J . Brezden  and A.L. Redenbach f o r t h e i r h e l p i n t h e l a b o r a t o r y , and M i s s E.A. B e a t t i e f o r h e r encouragement. T h i s r e s e a r c h was undertaken s u p p o r t o f t h e N a t i o n a l Research  with the f i n a n c i a l  C o u n c i l o f Canada and A.G.  Magee t o whom s p e c i a l thanks a r e accorded.  xv  Chapter 1  INTRODUCTION AND THEORY  1.1  P r a c t i c a l S i g n i f i c a n c e of Liquid-phase S i n t e r i n g L i q u i d - p h a s e s i n t e r i n g i s the s i n t e r i n g o f m e t a l  powders o r c e r a m i c m a t e r i a l s i n the p r e s e n c e o f a l i q u i d phase.  I n m e t a l powder systems i t i s most commonly accom-  p l i s h e d by m i x i n g t h e powders o f two o r more d i f f e r e n t m e t a l s (and/or a l l o y s ) , compacting t h e m i x t u r e and h e a t i n g i t t o a temperature above t h e m e l t i n g p o i n t o f one o f the powders b u t below t h a t o f a t l e a s t one o f t h e o t h e r powders. Generally, liquid-phase s i n t e r i n g leads to rapid t i o n o f t h e compact.  densifica-  E x c e p t i o n s a r e cases i n w h i c h t h e  l i q u i d does n o t 'wet' the s o l i d , when t h e r e i s a v e r y s m a l l amount o f l i q u i d formed, o r when u n u s u a l e x p a n s i o n p r o c e s s e s operate. The d r i v i n g f o r c e f o r the d e n s i f i c a t i o n o f powder compacts i s t h e r e d u c t i o n o f t h e i r t o t a l s u r f a c e energy. When a l i q u i d phase i s p r e s e n t , because o f s u r f a c e energy relationships,  t h e l i q u i d spreads t h r o u g h o u t t h e compact,  f i l l i n g t h e v o i d s between s o l i d p a r t i c l e s .  The  w h i c h r e s u l t range between the two extremes o f : 1  structures  2  i)  A continuous network of the s o l i d p a r t i c l e s with the l i q u i d phase d i s t r i b u t e d among t h e v o i d s i n t h e n e t w o r k and,  ii)  A s t r u c t u r e c o n s i s t i n g of s o l i d p a r t i c l e s s e p a r a t e d by t h e low m e l t i n g ' b i n d e r ' phase ( o n l y the b i n d e r phase i s c o n t i n u o u s ) .  The h i g h r a t e s o f d e n s i f i c a t i o n , and t h e a b i l i t y  to  produce s t r u c t u r e s o f h i g h d e n s i t y , w i t h c o r r e s p o n d i n g l y good mechanical  p r o p e r t i e s , makes l i q u i d - p h a s e s i n t e r i n g an  t i v e process  f o r the manufacture o f s m a l l m e t a l p a r t s .  attracIf  t h e volume f r a c t i o n o f the compacts which i s l i q u i d i s n o t excessive  ( i . e . i f t h e r e i s l e s s than 40% l i q u i d )  g e n e r a l l y r e t a i n t h e i r shape by v i r t u e of the a c t i o n of the l i q u i d . The  they  capillary  Thus the use o f moulds i s n o t  necessary.  a b i l i t y t o c o n t r o l and p r e d i c t s h r i n k a g e  during  l i q u i d - p h a s e s i n t e r i n g i s i m p o r t a n t because cUose d i m e n s i o n a l t o l e r a n c e s a r e o f utmost concern parts.  i n the manufacture o f s m a l l  I n o r d e r t o be a b l e t o p r e d i c t the s h r i n k a g e  during  s i n t e r i n g i t i s i m p o r t a n t t o have a c l e a r u n d e r s t a n d i n g t h e mechanisms and r a t e s o f the p r o c e s s e s  causing  of  shrinkage.  I t i s a l s o d e s i r a b l e t o be a b l e t o p r e d i c t the e f f e c t s o f a l t e r i n g such parameters as powder p a r t i c l e s i z e and i n g temperature.  I n f a c t , i n most l i q u i d - p h a s e s i n t e r i n g  systems v e r y l i t t l e i s understood densification.  sinter-  of the processes  causing  3  I r o n - c o p p e r m i x t u r e s a r e w i d e l y used i n c o n v e n t i o n a l powder m e t a l l u r g y because t h e p r o d u c t o f s i n t e r i n g has good mechanical p r o p e r t i e s .  F o r t h a t r e a s o n , t h e l i q u i d phase  s i n t e r i n g o f i r o n copper m i x t u r e s has been i n v e s t i g a t e d extensively i n the past.  1.2  I r o n - c o p p e r Phase E q u i l i b r i a From t h e i r o n - c o p p e r phase diagram i n F i g u r e 1 i t  i s p o s s i b l e t o a n a l y z e t h e sequence o f events which  will  o c c u r when a m i x t u r e o f i r o n and copper powders i s h e a t e d , from below t h e m e l t i n g p o i n t o f copper, t o above 1096°C.  It  i s assumed t h a t t h e m i x t u r e i s h e a t e d s u f f i c i e n t l y f a s t t h a t l i t t l e o r no i n t e r d i f f u s i o n o c c u r s u n t i l t h e copper has m e l t e d . The sequence o f events i s as f o l l o w s : i) ii) iii)  Copper  me I t s ( I 0 8 4 ° C )  Liquid  copper  iron  Some e - p h a s e ( s o l i d s o l u t i o n based on c o p p e r ) may f o r m b e t w e e n I084°C  and  iv)  d i s s o l v e s some  I096°C  Copper begins t o d i f f u s e i n t o s o l i d i r o n t o form Y~ °l'd solution s  V)  vi)  A t I096°C, a n y c o p p e r - r i c h s o l i d (e) decomposes t o form c o p p e r - r i c h l i q u i d and c o p p e r s a t u r a t e d s o l i d y Copper  continues to diffuse  into y  W i t h p r o l o n g e d h o l d i n g above 1096°C, t h e y becomes s a t u r a t e d w i t h copper.  I f t h e t o t a l amount o f copper p r e s e n t  4  Cu-Fe  Atomic Percentage  °c  10  1600 2800 F  30  40  1  1  Copper  50  60  70  80  —1  1538°  90 I  1  ""  L »/  I480°,I0.3 /o  2700F  (8-Fe)-r 2500F  20  -1  1500 1400  Copper-Iron  1  1394°  !  1300 2300 F  1200 2I00F  - (X-Fe) I I  1100  /  C  1096°  -9.5  )  N1 1  96- K^ /  1 1  9 I 2 1000 I900F  108'» . 5 ° - ^ \  1800 F  (Cu)*-  900  I600F  (a-Fe)  -N2.I  800  700Fe  CURIE TEN PERATURE 111111111  10  Robert E. Johnson  20  30  40  1 1  -99 \  851°  50  60  70  80  Weight Percentage Copper  F i g u r e 1. Fe-Cu phase diagram [ 1 ] .  90  Cu  5  i s l e s s than the s o l u b i l i t y l i m i t i n y the l i q u i d phase w i l l disappear.  O t h e r w i s e , an e q u i l i b r i u m i s e s t a b l i s h e d between  an i r o n - s a t u r a t e d l i q u i d s o l u t i o n and a c o p p e r - s a t u r a t e d y solid  solution. Because t h e l a t t i c e parameter o f y i r o n i s l i t t l e  a l t e r e d by copper i n s o l u t i o n  ( i n amounts l e s s t h a n t h e  s o l u b i l i t y l i m i t ) , the expansion o f i r o n p a r t i c l e s , when copper i s d i s s o l v e d i n them, i s a p p r o x i m a t e l y e q u a l t o t h e amount o f copper d i s s o l v e d .  A pure i r o n p a r t i c l e expands  a p p r o x i m a t e l y 8 p e r c e n t i n volume when i t d i s s o l v e s 8 p e r c e n t copper by  weight.  The i n t e r f a c i a l  i n t e r a c t i o n o f t h e l i q u i d and  iron-  r i c h s o l i d p a r t i c l e s above the m e l t i n g p o i n t o f copper i s o f g r e a t importance  i n d e t e r m i n i n g the n a t u r e o f t h e p r o c e s s e s  leading to d e n s i f i c a t i o n during liquid-phase s i n t e r i n g .  The  most s i g n i f i c a n t i n t e r a c t i o n s a r e t h o s e r e l a t i n g t o t h e w e t t i n g o f t h e s o l i d s u r f a c e s by  liquid.  The w e t t i n g c h a r a c t e r i s t i c s o f a l i q u i d - s o l i d a r e commonly d e s c r i b e d by two parameters:  the contact angle,  0, and t h e d i h e d r a l a n g l e , <J>, as d e f i n e d i n the n e x t The s i g n i f i c a n c e o f t h e s e parameters  system  section.  must be c l e a r l y under-  s t o o d and t h e i r v a l u e s known b e f o r e i t i s p o s s i b l e t o t h e o r i z e on the p r o c e s s e s l e a d i n g t o d e n s i f i c a t i o n d u r i n g t h e phase s i n t e r i n g o f i r o n - c o p p e r compacts.  liquid-  6  1.3  Role o f S u r f a c e E n e r g i e s i n L i q u i d - p h a s e 1.3.1  Sintering  C o n t a c t and D i h e d r a l A n g l e s The  a n g l e o f c o n t a c t w h i c h a l i q u i d makes w i t h a  s o l i d i n t h e p r e s e n c e o f a vapour i s c a l l e d t h e c o n t a c t (9).  If Y  l v  i  angle  l i q u i d - v a p o u r i n t e r f a c i a l energy and Yg-y  s t n e  i s t h e s o l i d - v a p o u r i n t e r f a c i a l energy t h e n :  cos e =  Y  s  ^  v v Y  Where Y 2).  s l  i s the s o l i d - l i q u i d  S  (1.1)  L  LV  i n t e r f a c i a l energy (see F i g u r e  I f 9 i s l e s s than 90° t h e l i q u i d i s s a i d t o wet t h e  s o l i d , and i f 0 = 0° t h e w e t t i n g i s c h a r a c t e r i z e d as 'complete' A low c o n t a c t angle i s f a v o u r e d : A)  For a given  B)  For a given  solid  liquid  by:  by:  i)  a  low Yg|_>  ii)  a  l o w Y|_y  i) i i)  a high  Ygy  a  Y  low  and  S L  I t s h o u l d be noted t h a t 0 can never be zero as l o n g as t h e surface t e n s i o n of the l i q u i d the s o l i d  (Y  s v  (YTT?)  i-  higher than t h a t of  )•  I f 0 i s l e s s than 90° and y i n c r e a s e s when Y increased.  s  l v  i  s  reduced.  If Y  O T  s l  i s c o n s t a n t then 0 i s increased, 6 i s  I n a c o m p l e t e l y w e t t i n g system t h e l i q u i d  will  coat a l l o f the surfaces o f the s o l i d which are i n contact  7  \\\\\Ys^X\\\\\\\\ F i g u r e 2.  The c o n t a c t angle', 0; d e t e r m i n e d by t h e r e l a t i v e values of a , a and d . (a = i n t e r f a c i a l t e n s i o n = y x a r e a ; where y = i n t e r f a c i a l energy) g L  g v  L V  8  w i t h vapour.  I f 6 i s greater  90°  the l i q u i d  'sweats' out  of  the compact. G r a i n boundary p e n e t r a t i o n  i s d e t e r m i n e d by  the  d i h e d r a l a n g l e , <J), w h i c h i s a f u n c t i o n o f the r e l a t i v e magni tude o f the g r a i n boundary and energies  (see Figure©3).  The  solid-liquid  interfacial  e q u a t i o n d e f i n i n g the  dihedral  angle i s :  COS  where Y  s s  i  Y  l2j  2  SS  (1  ^SL  i s the g r a i n boundary i n t e r f a c i a l  energy.  I n a powder compact complete l i q u i d p e n e t r a t i o n a g r a i n boundary (or s o l i d p a r t i c l e - s o l i d o c c u r s when y i s greater  S L  than  i  s  l e s s than i y  i Ygg'  ^ -"- ? s  r e a  s s  particle  ( i . e . cj) = 0 ) .  ter.than  contact), When  zero and  of  y  S L  l e s s than  180°. A c c o r d i n g t o Smith [ 2 ] , i f the d i h e d r a l a n g l e i s g r e a t e r t h a n z e r o d e g r e e s , l i q u i d w i l l p e n e t r a t e the  grain  boundary o n l y t o the p o i n t where i t makes an a n g l e i n t h e boundary e q u a l t o (f). The  l i q u i d o n l y advances f u r t h e r i n t o  the boundary by d i s s o l v i n g the s o l i d where i t f o r c e s l i q u i d t o make an a n g l e w i t h i t s e l f e q u a l t o the angle, ( i f the s o l i d i s s o l u b l e i n the  the  dihedral  liquid).  A f u r t h e r e f f e c t o f s u r f a c e energy i n s i n t e r i n g systems i s t h a t , t h r o u g h c a p i l l a r y  liquid-phase  pressure,  the  9  iDy / ° ~  /  Solid  S L  Liquid  Solid  °SS  Figure  3.  The d i h e d r a l a n g l e , <J); a f u n c t i o n o f t h e r e l a t i v e magnitudes o f Y Yod-tor a and a ) . a  q t  n  d  c c  10  l i q u i d p l a c e s the s o l i d p a r t i c l e s under compressive s t r e s s . A l i q u i d w i t h 0 = 0 ° w i l l coat the s o l i d p a r t i c l e and pores w i l l form i n the l i q u i d .  surfaces  According to Kingery  the c a p i l l a r y p r e s s u r e f o r c i n g a d j a c e n t p a r t i c l e s  [3]  together  due t o the p r e s e n c e o f a c o m p l e t e l y w e t t i n g l i q u i d between them i s : (1.3) Where P i s the p r e s s u r e and r , the r a d i u s o f l i q u i d ( p o r e ) , (see F i g u r e 4 ) .  surface  The r e l a t i o n s h i p a p p l i e s whether o r  not the l i q u i d p e n e t r a t e s the p o i n t of c o n t a c t between two adjacent p a r t i c l e s  ( i . e . i t i s t r u e f o r cf> > 0) .  G e s s i n g e r , F i s h m e i s t e r and Lukas [4] have shown t h a t a compressive s t r e s s e x i s t s a l s o f o r p a r t i a l l y w e t t i n g  liquids,  but i t i s not as l a r g e as i n c o m p l e t e l y w e t t i n g systems.  1.3.2  F a c t o r s A f f e c t i n g the C o n t a c t and D i h e d r a l A n g l e s A c c o r d i n g t o T a y l o r [5] t h e f o r m a t i o n o f a t r a n s i t i o n  zone between the s o l i d and l i q u i d , i n the form o f an  inter-  m e t a l l i c compound o r s o l i d s o l u t i o n , can a l t e r the v a l u e o f YOT  a n d  t h e r e b y change the c o n t a c t a n g l e .  Eremenko [6]  has  p o i n t e d out t h a t a c h a r a c t e r i s t i c f e a t u r e of the s u r f a c e f r e e energy o f m e t a l s  i s the e x t r a o r d i n a r y dependence o f Y  even v e r y s m a l l amounts o f i m p u r i t i e s .  l v  on  11  F i g u r e 4.  S p h e r i c a l p a r t i c l e s h e l d t o g e t h e r by c a p i l l a r y p r e s s u r e o f t h e l i q u i d phase; cj> i s e q u a l t o z e r O j i n t h e example shown, r i s t h e r a d i u s of t h e p o r e .  12 The d i h e d r a l angle i s p a r t l y dependent on t h e v a l u e of Y  S S  f w h i c h i s c o n s i d e r e d t o v a r y w i t h t h e degree o f m i s -  o r i e n t a t i o n a c r o s s t h e g r a i n boundary [ 7 ] . 5% o f randomly o r i e n t e d g r a i n b o u n d a r i e s  Approximately  a r e low-energy  b o u n d a r i e s , f o r w h i c h t h e v a l u e o f cf> i s h i g h e r t h a n f o r t h e o t h e r 95% [ 7 ] . I n l i q u i d - s o l d l d s s y s f e e m s w w i f c h i / i n t r i n s ' i c a l l y low d i h e d r a l a n g l e s , r e l a t i v e l y s m a l l changes i n y changes i n t h e d i h e d r a l a n g l e .  s s  cause l a r g e  A l s o , the adsorption of  i m p u r i t i e s on s o l i d s u r f a c e s can s i g n i f i c a n t l y a l t e r s u r f a c e e n e r g i e s and thus t h e v a l u e s o f 9 and system [ 8 ] .  their  cf> i n a g i v e n  The d i h e d r a l angle i s a l s o s e n s i t i v e t o a d d i t i o n s  t o t h e l i q u i d phase [ 4 ] .  Van V l a c k  [9] has shown t h a t , i n  the FeS/FeO/Fe system, i n c r e a s e d i r o n c o n t e n t s i n t h e l i q u i d cause a lower d i h e d r a l a n g l e .  The v a l u e o f <f> a l s o v a r i e s  w i t h temperature [ 9 ] .  1.3.3  W e t t i n g i n t h e Fe-Cu System S e v e r a l d e t e r m i n a t i o n s o f t h e v a l u e o f <j> and 0 f o r  t h e Fe-Cu system have been made.  They a r e r e p o r t e d i n T a b l e I .  The v a l u e s f o r 9 v a r y w i t h t h e atmosphere used.  Specifically,  complete w e t t i n g (0 = 0°) was observed o n l y when a r e d u c i n g atmosphere was employed. The observed v a l u e s o f t h e d i h e d r a l a n g l e v a r y w i t h temperature.  T h e o r e t i c a l l y , they s h o u l d n o t v a r y w i t h  13  Table I R e s u l t s o f P r e v i o u s S u r f a c e Energy and C o n t a c t and D i h e d r a l A n g l e Measurements i n t h e Fe-Cu System Temperature C o n t a c t D i h e d r a l SS SL Degrees Angle, Angle, Atmosphere R e f e r e n c e C e n t i g r a d e Degrees Degrees gm/cm gm/cm Y  Y  2  0  —  H  27  1160  30  1220  30  1105  25  1100 1130  *  23  1130  *  —  850.  0.51 430.  34  444.  Ar  34  444.  Ar  387.  Ar  301.  Ar  13  *  7 J  11 J  1H /4N I  9  1150  —  0.51  **  10  2  1.0  **  1100  2  2  2  1180  21  1H /4N  1110  32  1H /4N J  2  2  780.  1100  *  r e l a t i v e values **  a f t e r 30 minutes a t temperature  Vacuum  2  12  2  13  14 d i f f e r e n t atmospheres, because t h e e q u a t i o n  f o r cj> does n o t  include y „ . T  LiV  Hough and R o l l s  [1.1] found t h a t 6 d e c r e a s e d l i n e a r l y  d u r i n g p e r i o d s o f up t o 30 minutes and t h e n remained c o n s t a n t . They c o n c l u d e d t h a t a l l o y i n g o f t h e i r o n and t h e l i q u i d phase was t h e cause o f t h e d e c r e a s e i n 0.  1.4  Mechanisms o f L i q u i d - p h a s e S i n t e r i n g 1.4.1  Rearrangement Kingery  [3] proposed t h a t upon i n i t i a l f o r m a t i o n o f  the  l i q u i d phase, c a p i l l a r y p r e s s u r e w i l l r e a r r a n g e (repack)  the  s o l i d p a r t i c l e s i n such a manner t h a t  maximum p a c k i n g  d e n s i t y and minimum pore s u r f a c e a r e a w i l l r e s u l t .  The r e -  p a c k i n g i s a c c o m p l i s h e d by t h e s l i d i n g o f s o l i d p a r t i c l e s p a s t each o t h e r . spherical  He noted t h a t i f t h e s o l i d p a r t i c l e s  complete d e n s i f i c a t i o n  l a r g e amounts o f l i q u i d .  remain  i s only possible with  A minimum o f 35% (by volume) o f  l i q u i d i s required to f i l l  t h e v o i d s between u n i f o r m - s i z e d  s o l i d spheres packed f o r maximum d e n s i t y . Kingery  i d e n t i f i e d v i s c o u s f l o w as t h e r a t e -  c o n t r o l l i n g p r o c e s s i n rearrangement, from which a l i n e a r dependence o f d e n s i f i c a t i o n  on time i s p r e d i c t e d .  Kingery  proposed t h e r e l a t i o n s h i p :  AL/Lo = 1/3 (AV/V ) = t 0  (  1  +  y  )  (1.4)  15  where L and V a r e the l e n g t h and volume-of the compact, and  y  1  i s t h e c o r r e c t i o n f o r i n c r e a s i n g r e s i s t a n c e t o rearrangement when t h e r e p a c k i n g nears c o m p l e t i o n , and f o r an i n c r e a s i n g d r i v i n g f o r c e due t o e v e r d e c r e a s i n g p o r e s i z e . r e f e r t o o r i g i n a l dimensions Rearrangement  (i.e.  L  0  and  V  0  a t the s t a r t o f t h e p r o c e s s ) .  i s o n l y p o s s i b l e f o r a s h o r t t i m e and  once maximum p a c k i n g d e n s i t y i s a c c o m p l i s h e d i t w i l l  cease  i n t h o s e systems i n w h i c h the s o l i d p a r t i c l e s do n o t d i s s o l v e i n the l i q u i d .  1.4.2  S o l u t i o n - p r e c i p i t a t i o n Theories S e v e r a l mechanisms o f d e n s i f i c a t i o n and g r a i n growth  d u r i n g l i q u i d - p h a s e s i n t e r i n g have been proposed w h i c h depend on t h e s o l u b i l i t y o f the s o l i d i n t h e l i q u i d .  Because  iron  has an a p p r e c i a b l e s o l u b i l i t y i n l i q u i d copper t h e s e t h e o r i e s may w e l l a p p l y t o t h e Fe-Cu system. Kingery  [3] proposed a mechanism o f d e n s i f i c a t i o n  w h i c h he c a l l e d " s o l u t i o n - p r e c i p i t a t i o n " b u t w h i c h , i n o r d e r to d i s t i n g u i s h i t from o t h e r mechanisms, w i l l be r e f e r r e d t o i n t h i s work as ' s o l u t i o n due t o p r e s s u r e ' . A c c o r d i n g t o t h e model, which a p p l i e s o n l y t o systems w i t h a c o m p l e t e l y w e t t i n g liquid  (and presumably a z e r o d i h e d r a l a n g l e ) , the l i q u i d  c o a t s t h e s u r f a c e o f t h e s o l i d p a r t i c l e s and p e n e t r a t e s s o l i d - s o l i d c o n t a c t s between p a r t i c l e s . of  The c a p i l l a r y p r e s s u r e  t h e l i q u i d e x e r t s compressive p r e s s u r e s on t h o s e areas o f ^"y i s a s m a l l f r a c t i o n .  16  the s o l i d p a r t i c l e s which are s e p a r a t e d from o t h e r s o l i d p a r t i c l e s by o n l y t h i n f i l m s o f l i q u i d , and the a c t i v i t y o f the s o l i d i s l o c a l l y i n c r e a s e d . The s t r e s s a t the c o n t a c t areas i s p r o p o r t i o n a l t o the amount o f c a p i l l a r y p r e s s u r e , and thus the s i z e o f the pores i n the l i q u i d .  The i n c r e a s e d a c t i v i t y p r o v i d e s a  d r i v i n g f o r c e f o r the s e l e c t i v e s o l u t i o n o f s o l i d a t ' c o n t a c t s ' , w h i c h a l l o w s the approach o f p a r t i c l e c e n t r e s and, t h e r e f o r e , densification.  The  s o l i d d i s s o l v e d at 'contacts' r e - p r e c i p i -  t a t e s a t o t h e r areas o f the s o l i d w h i c h are n o t under comp r e s s i v e s t r e s s ; thus promoting  a l t e r a t i o n o f the shape o f  the s o l i d p a r t i c l e s t o allow increased packing  efficiency  (density). Kingery  [3] p r e d i c t e d t h a t s h r i n k a g e r e s u l t i n g  s o l u t i o n due t o p r e s s u r e , w i t h d i f f u s i o n would be governed by the e q u a t i o n  from  rate-controlling,  [14]:  AL/Lo = C i r " -  7  3  t  l  /  (1.5)  3  where ' r ' i s the p a r t i c l e r a d i u s , ' t ' t h e time from the s t a r t o f t h e p r o c e s s and and temperature.  * C i ' a constant f o r a given  composition  I f t h e phase-boundary r e a c t i o n i s r a t e -  c o n t r o l l i n g the e q u a t i o n i s :  AL/Lo = C  2  r  -  1  t  2  (1.6)  17  where C  2  i s a constant f o r a g i v e n composition Bockstiegel  and temperature.  [15] has suggested t h a t a s k e l e t a l  net-  work o f s o l i d p a r t i c l e s permeated by l i q u i d may s h r i n k by a process  o f s o l u t i o n and r e - r p r e c i p i t a t i o n o f - t h e s o l i d i n the  l i q u i d phase "with the s o l i d more completely ing  . . . s k e l e t o n becoming  enclosed by l i q u i d  ever  . . . and t h e r e f o r e s h r i n k -  as a whole" [15]. He d i d n o t e l a b o r a t e , but i t i s i n f e r r e d t h a t the  theory  i s based on the i d e a t h a t s o l i d a t the s u r f a c e o f the  compact d i s s o l v e s and i s t r a n s p o r t e d t o i n n e r areas o f the compact where i t r e - p r e c i p i t a t e s on the s o l i d network.  In  t h i s manner the e x t e r n a l dimensions o f the s o l i d network are reduced and d e n s i f i c a t i o n r e s u l t s . to apply t o systems with a completely  The theory wetting  i s expected  l i q u i d but a  f i n i t e d i h e d r a l angle. In many l i q u i d - p h a s e s i n t e r i n g systems, the s o l i d phase g r a i n s  (or p a r t i c l e s ) a r e observed t o i n c r e a s e i n  average s i z e w i t h i n c r e a s i n g time a t temperature. growth process was f i r s t d i s c u s s e d and analysed S m i t h e l l s and W i l l i a m s  by P r i c e ,  [1.6] i n r e f e r e n c e t o W-Cu-Ni a l l o y s ,  and was d e s c r i b e d l a t e r by L e n e l Mechanism."  This  [17] as the "Heavy A l l o y  The mechanism i n v o l v e s the s o l u t i o n o f s m a l l  s o l i d g r a i n s i n the l i q u i d and r e - p r e c i p i t a t i o n on the l a r g e r s o l i d grains.  18  The d r i v i n g f o r c e f o r the p r o c e s s i s the i n c r e a s e d s o l u b i l i t y o f s o l i d a t a curved s u r f a c e a c c o r d i n g t o the relationship: Ira (S/S-b) = 2 Y where S/So  s l  V /RkT  (1.7)  0  i s the r a t i o o f the s o l u b i l i t y a t a c u r v e d s u r f a c e  of r a d i u s R to t h a t at a f l a t s u r f a c e , V  0  i s the m o l e c u l a r  volume, k, the Boltzmann c o n s t a n t and, T the a b s o l u t e temperature.  Thus, i n a powder compact t h e s o l u b i l i t y o f a p a r t i c l e  increases with decreasing radius.  1.4.3  Coalescence Coalescence  i s a p r o c e s s o f d e n s i f i c a t i o n analogous  to s o l i d s t a t e s i n t e r i n g . d i f f u s i o n , or p l a s t i c  Presumably, by means o f volume  f l o w mechanisms a c t i n g i n t h e  solid,  p a r t i c l e s i n c o n t a c t w i t h each o t h e r grow t o g e t h e r w i t h enlargement o f the c o n t a c t a r e a  (neck) between them.  t o t a l s o l i d - l i q u i d o r s o l i d vapour i n t e r f a c i a l a r e a  The (and  thus the t o t a l s u r f a c e energy o f the system) i s t h e r e b y  reduced.  White [7] has shown t h a t the t h e o r e t i c a l s u r f a c e energy o f two spheres i n p o i n t c o n t a c t i n a s u r r o u n d i n g may  be reduced by c o a l e s c e n c e .  A d j a c e n t s o l i d spheres  m i n i m i z e t h e i r s u r f a c e energy by approaching  each o t h e r  liquid may through  c o a l e s c e n c e and the f o r m a t i o n o f a ( f l a t ) i n t e r f a c e between them.  The energy o f the two spheres  i s a minimum when they  19  i n t e r s e c t a t an angle e q u a l t o t h e d i h e d r a l a n g l e o f t h e s o l i d - l i q u i d system [ 7 ] .  The t h e o r y i n c l u d e s c o n s e r v a t i o n  o f t h e volume o f t h e s p h e r e s . ' F u r t h e r d i s c u s s i o n o f c o a l e s c e n c e may be found i n a paper by Warren [1.9] .  1.5  P r e v i o u s S t u d i e s o f t h e Fe-Cu System 1.5.1  Earliest  Observation  P r i c e , S m i t h e l l s and W i l l i a m s  [16] r e p o r t e d i n 1938  t h a t an 80% i r o n , 20% copper powder m i x t u r e s i n t e r e d f o r t h r e e hours a t 1400°C reached  93% o f t h e o r e t i c a l d e n s i t y , and  e x h i b i t e d a s t r u c t u r e o f rounded g r a i n s o f " i r o n " i n a m a t r i x o f copper s a t u r a t e d w i t h i r o n .  Since then, the liquid-phase  s i n t e r i n g o f Fe-Cu m i x t u r e s has been t h e s u b j e c t o f many investigations  [6,12,14,15,16,20,21,22,23,24,25,26,27,28,29],  t h e more i m p o r t a n t o f w h i c h a r e d e s c r i b e d below.  1.5.2  Practical Investigations  Some p r e v i o u s i n v e s t i g a t i o n s have been p r i m a r i l y concerned w i t h m e c h a n i c a l  p r o p e r t i e s and measurements o f n e t  d i m e n s i o n a l changes i n s t a t i c runs f o r use i n powder m e t a l lurgy production. N o r t h c o t t and Leadbeater [20] s i n t e r e d s e v e r a l Fe-Cu m i x t u r e s under a v a r i e t y o f c o n d i t i o n s .  They observed maximum  20  sintered densities  i n m i x t u r e s c o n t a i n i n g 20% o r more o f  copper, and g r e a t e r s h r i n k a g e s w i t h f i n e r powders.  I n two  compacts o f 4 7 y  m  i r o n powder w i t h 4.74% and 14% copper they  observed s m a l l  (1.5 t o 3% AV/V ) n e t e x p a n s i o n s a f t e r  sinter-  0  i n g f o r one hour a t 1100°C.  Metallographic studies of the  s t r u c t u r e s a f t e r i t o 4 hours a t 1100°C r e v e a l e d "marked r o u n d i n g o f t h e i r o n p a r t i c l e s and e v i d e n c e o f t h e i r c o a l e s c e n c e even i n t h e h i g h copper a l l o y s  (35% c o p p e r ) . "  After  i hour  a t 1100°C a c l e a r l y marked d i f f u s i o n zone was o b s e r v e d i n t h e iron particles  (due t o copper d i f f u s i n g i n t o t h e i r o n ) .  Chadwick, B r o a d f i e l d  and Pugh [21] s i n t e r e d  i r o n - c o p p e r m i x t u r e s a t 1120°C.  7 5/25  They o b s e r v e d 1% l i n e a r  e x p a n s i o n a f t e r 15 minutes i n a compact made from 2 9 y with 3y  m  copper powders.  I n a compact p r e p a r e d from  i r o n and copper powders ( 4 9 y  m  d i a m e t e r i r o n and 1 2 y  they o b s e r v e d 9% l i n e a r s h r i n k a g e . different i n i t i a l densities.  larger m  copper)  The two compacts had  Microstructural  showed t h a t t h e s i n t e r e d t s t e u c t u r e f o f  iron  m  investigation  a!575/>S25;ocomp.act-was  " i r o n - r i c h f e r r i t i c p a r t i c l e s o f rounded form i n c o n t i n u o u s c o n t a c t , t h e i n t e r m e d i a t e spaces b e i n g s u b s t a n t i a l l y by t h e c o p p e r - r i c h phase," Silbereisen  (see F i g u r e 5 ) .  [ 2 2 ] , i n an i n v e s t i g a t i o n  compensation" by a l l o y i n g , i n v e s t i g a t e d i r o n powder compacts, sintered  filled  of "shrinkage  the expansion o f  c o n t a i n i n g up t o 8 p e r c e n t copper,  a t t e m p e r a t u r e s between 1000°C and 1250°C.  He  21  F i g u r e 5.  M i c r o s t r u c t u r e o f a 75/25 Fe-Cu compact s i n t e r e d a t 1120°C f o r an u n s p e c i f i e d time (not l e s s t h a n 15 minutes) , from Chadwick et al. [21] 50Ox. The copper i s w h i t e and t h e i r o n o f v a r i o u s shades, from l i g h t grey t o b l a c k .  22  observed  i n c r e a s i n g amounts o f n e t e x p a n s i o n w i t h h i g h e r  copper c o n t e n t s , and p r o g r e s s i v e l y l e s s e x p a n s i o n sintering  after  ( f o r a f i x e d time) a t h i g h e r temperatures  above  1100°C.  1.5.3  Dilatometer Studies S e v e r a l i n v e s t i g a t o r s have used d i l a t o m e t e r s t o  f o l l o w the d i m e n s i o n a l changes o f Fe-Cu compacts d u r i n g liquid-phase sintering. Kingery  [1.4] s i n t e r e d compacts c o n t a i n i n g 11.3,  22.0  and 43.0 weight p e r c e n t copper m i x t u r e s a t 1150 C i n a o  d i l a t o m e t e r w i t h a hydrogen atmosphere, u s i n g a s h o r t heat-up period.  A p o r t i o n o f hiLssdataaissshown i n F i g u r e 6.  The  p l o t s o f l o g ( A V / V ) v e r s u s l o g time were c l a i m e d t o be 0  l i n e s w i t h i n i t i a l s l o p e s o f 1.3 the l a t e r p o r t i o n s . of p a r t i c l e s i z e .  t o 1.4  straight  and s l o p e s o f 1/3  in  Kingery a l s o i n v e s t i g a t e d the e f f e c t  He concluded t h a t 'rearrangement  and  1  ' s o l u t i o n due t o p r e s s u r e ' were t h e mechanisms c a u s i n g d e n s i f i cation.  K i n g e r y a p p a r e n t l y d i d not observe  any e x p a n s i o n i n  h i s compacts d u r i n g s i n t e r i n g . I n 1959 B o c k s t i e g e l [15] observed t h a t i n 20% 80% i r o n powder m i x t u r e s the compacts expanded r a p i d l y e x t e n s i v e l y - u p t t o 2.7%  (AL/Lo) i n the 10 minutes  f o l l o w i n g m e l t i n g , and then c o n t r a c t e d more s l o w l y . 7 shows h i s r e s u l t s f o r s i n t e r i n g experiments  copper, and  immediately Figure  a t 1150°C w i t h  23  0021  F i g u r e 6.  i  i  1 2  5  10  20  50  TIME (MINUTES)  100 200 500  Log f r a c t i o n a l d e n s i f i c a t i o n v e r s u s l o g t i m e , f o r Fe-Cu compacts c o n t a i n i n g 11.3, 22.0 and 43 weight per cent copper a t 1150°C, from K i n g e r y [14] .  24  d i f f e r e n t copper c o n t e n t s . i n 20% copper m i x t u r e s ,  Maximum e x p a n s i o n was  realized  w h i c h a l s o c o n t r a c t e d most r a p i d l y .  F i g u r e 8 shows t h e r e s u l t s o f a s e r i e s o f runs o f 7.5% Cu m i x t u r e s w i t h v a r i o u s powder s i z e s .  They i n d i c a t e  some c r i t i c a l powder s i z e , near 1 4 5 y expansion  m  that at  d i a m e t e r , maximum  occurred. Bockstiegel  [15] was a b l e t o show t h a t one cause o f  the e x p a n s i o n was t h e d i f f u s i o n o f copper i n t o i r o n p a r t i c l e s F o r example, he observed no e x p a n s i o n d u r i n g t h e l i q u i d - p h a s e s i n t e r i n g of i r o n - s i l v e r mixtures,  w h i c h he r e l a t e d t o t h e  low s o l u b i l i t y o f s i l v e r i n i r o n .  Bockstiegel  that shrinkage  [1.5] proposed  o c c u r r e d by s o l u t i o n and r e - p r e c i p i t a t i o n o f  t h e s o l i d w h i c h , he c o n c l u d e d , was i n t e r c o n n e c t e d throughout s i n t e r i n g . e x p a n s i o n and s h r i n k a g e  (skeletal)  He d e v e l o p e d e q u a t i o n s f o r b o t h t h e stages.  U s i n g them he showed,  s c h e m a t i c a l l y , how t h e r a t e s o f t h e two p r o c e s s e s would v a r y depending on t h e s p e c i f i c s u r f a c e a r e a o f t h e i r o n powder and t h e mass t r a n s p o r t c a p a c i t y o f t h e l i q u i d . Dautzenberg [23] used a d i l a t o m e t e r t o i n v e s t i g a t e the l i q u i d - p h a s e s i n t e r i n g o f p r e a l l o y e d Fe-Cu powders and an Fe-3%  Cu powder m i x t u r e .  I n the l a t t e r m i x t u r e he o b s e r v e d  e x p a n s i o n f o l l o w e d by c o n t r a c t i o n .  He proposed t h a t t h e  e x p a n s i o n and c o n t r a c t i o n were t h e r e s u l t o f t h e f o r m a t i o n and subsequent m e l t i n g o f t h e s o l i d e-phase w h i c h e x i s t s between 1084°C and 1096°C.  o oT  c  <0  /  <D  t—  T em  1—  800  0)  o. E  i  T e m p e ra t u re  WO  0 3.0  /  1  ^ M e 11 I ng f o i n t i of C o p f )e r 3  /  /  °o  •"Me 1 1 ting o  oe r  25 aJt r e  i nt  Cop  :  \  i  •'•  Grs i n Den  S i 2  r/cm : 3  s  ' y,i 1  <I50 6.3  i  sj/TJ  >200 <m  \ <20  i  5.3  i  \<7  \5.3 20  W  60  80  100  130  110  Sintering  F i g u r e 7.  C U  - (AL/L)  20  T i m e ,  The e f f e c t o f copper c o n t e n t on t h e s i n t e r i n g behaviour of Fe-Cu compacts o f <150u powders a t 1150°C from Bockstiegel [15]. [(AL/L)  0  0  W  60  80  Minutes  F i g u r e 8.  wo  m  The e f f e c t o f powder s i z e on t h e s i n t e r ing behaviour (at 1150°C) o f Fe-7.5Cu compacts, from B o c k s t i e g e l [15] .  i n %] i s t h e d i m e n s i o n a l change  o f an i r o n - c o p p e r compact r e l a t i v e t o a pure i r o n compact o f t h e same powder s i z e .  26  In metallographic  i n v e s t i g a t i o n s w i t h a hot stage  m i c r o s c o p e a t 1100°C and 1150°C, Dautzenberg  observed  p e n e t r a t i o n o f t h e i r o n g r a i n b o u n d a r i e s by copper.  He  remarked t h a t a t 1150°C t h e p e n e t r a t e d g r a i n b o u n d a r i e s had "widened s i g n i f i c a n t l y " [ 2 3 ] . T r u d e l and Angers  [24] a l s o i n v e s t i g a t e d t h e s i n t e r -  i n g o f Fe-Cu-C powder m i x t u r e s u s i n g a d i l a t o m e t e r .  They  observed s m a l l e x p a n s i o n s [0.5% (AL/Lo)] f o l l o w e d by s m a l l srlow c o n t r a c t i o n s  [<0.7% (AL/Lo)] i n m i x t u r e s c o n t a i n i n g 0 t o  12.8% copper and one p e r c e n t g r a p h i t e , which were s i n t e r e d a t 1120°C f o r h a l f an hour.  They observed s i m i l a r e x p a n s i o n s  when p r e a l l o y e d powders were employed. was f o r an Fe-8.1%Cuv m i x t u r e . expanded l e s s .  The l a r g e s t e x p a n s i o n  A 12.8% copper m i x t u r e  I n t h a t m i x t u r e l i q u i d copper was p r e s e n t  t h r o u g h o u t s i n t e r i n g , as t h e s o l u b i l i t y l i m i t o f copper i n i r o n i s a p p r o x i m a t e l y 9.3% a t 1120°C. T r u d e l and Angers  [24] a l s o i n v e s t i g a t e d t h e r a t e  of d i f f u s i o n o f copper i n t o 6 0 y  m  d i a m e t e r Atomet i r o n powder  a t 1120°C and showed t h a t t h e d i f f u s i o n d i s t a n c e depth) was 8 y a f t e r 30 m i n u t e s . m  (penetration  Based upon t h e s o l u b i l i t y  of copper i n i r o n a t t h a t t e m p e r a t u r e , t h e maximum e x p a n s i o n r e s u l t i n g from t h a t e x t e n t o f d i f f u s i o n s h o u l d be a p p r o x i m a t e l y 2%  AV/V . 0  27  1.5.4  Other S t u d i e s L e n e l [25] i n v e s t i g a t e d t h e l i q u i d phase s i n t e r i n g  o f 80/20 Fe/Cu powder m i x t u r e s and p r e s e n t e d h i s d a t a as p l o t s o f a " d e n s i f i c a t i o n parameter"  versus the logarithm  o f t h e time a t t h e s i n t e r i n g t e m p e r a t u r e . gave s t r a i g h t l i n e p l o t s .  Some o f h i s d a t a  However, he was n o t a b l e t o  a t t r i b u t e t h a t r e s u l t t o any p a r t i c u l a r mechanism o f s i n t e r i n g . L e n e l a l s o i n v e s t i g a t e d t h e g r a i n growth o f t h e s o l i d  particles  d u r i n g s i n t e r i n g and c o n c l u d e d t h a t t h e "Heavy A l l o y Mechanism" o f s o l u t i o n - p r e c i p i t a t i o n might have been o p e r a t i n g . Ramakrishnan  and L a k s h i m i n a r a s i m h a n  [26] o b s e r v e d  i n c r e a s i n g amounts o f s h r i n k a g e a f t e r a g i v e n time a t 1100°C w i t h i n c r e a s i n g copper c o n t e n t s .  They a t t r i b u t e d t h e s e  o b s e r v a t i o n s t o i n c r e a s i n g c a p i l l a r y p r e s s u r e i n t h e compacts when more l i q u i d was p r e s e n t .  1.5.5  Expansion E f f e c t s B o c k s t i e g a l [15] a t t r i b u t e d t h e e x p a n s i o n he observed  t o d i f f u s i o n o f copper i n t o i r o n .  Dautzenberg  [23] suggested  t h a t t h e cause was t h e f r e e z i n g and m e l t i n g o f t h e e-phase between 1084°C and 1096°C.  " d e n s i f i c a t i o n  Silbereisen  p a r a m e t e r "  =  [22] proposed  that  ( S i n t e r e d  d e n s i t y - g r e e n  d e n s i t y  a b s o l u t e  d e n s i t y - g r e e n  d e n s i t y  x  1 0 0  28  the temperature dependence o f the amount o f e x p a n s i o n  (after  one hour o f s i n t e r i n g ) i n d i c a t e d t h a t t h e p r o c e s s was  not  o n l y t h e r e s u l t o f t h e d i f f u s i o n o f copper i n t o i r o n . T r u d e l and Angers  [24] c o n c l u d e d t h a t a p o r t i o n o f  the e x p a n s i o n was a r e s u l t o f g r a i n boundary p e n e t r a t i o n t h a t t h e p r e s e n c e o f carbon reduced "copper growth" by  and  reducing  the g r a i n boundary energy o f i r o n and thus t h e p e n e t r a t i o n of g r a i n b o u n d a r i e s by copper. B e r n e r , Exner and Petzow [12] s i n t e r e d Fe-Cu powder m i x t u r e s above 1100°C and performed copper experiments.  infiltration  They noted t h a t t h e observed e x p a n s i o n i n a  g i v e n time was more t h a n t w i c e as g r e a t as t h a t c a l c u l a t e d t o r e s u l t from d i f f u s i o n .  They r e l a t e d an o b s e r v e d  tempera-  t u r e dependence o f e x p a n s i o n t o an o b s e r v e d t e m p e r a t u r e dependence o f t h e d i h e d r a l a n g l e and c o n c l u d e d t h a t some o f t h e e x p a n s i o n was  a r e s u l t o f the p e n e t r a t i o n o f g r a i n b o u n d a r i e s .  They a l s o found t h a t l a r g e r copper p a r t i c l e s caused l a r g e r volume i n c r e a s e s .  No e x p a n s i o n was observed i n i r o n - s i l v e r  m i x t u r e s and t h i s was  a t t r i b u t e d t o the high d i h e d r a l angle  of the s i l v e r - ^ . i r o n system. B e r n e r et  al.  [12] a l s o observed l e s s e x p a n s i o n  during i n f i l t r a t i o n than during the l i q u i d - p h a s e s i n t e r i n g o f Fe-Cu m i x t u r e s , and found t h a t p r e s i n t e r i n g o f i r o n compacts b e f o r e i n f i l t r a t i o n reduced the amount and r a t e o f s w e l l i n g during i n f i l t r a t i o n .  The e f f e c t o f p r e s i n t e r i n g was  suggested  29  t o be t h e removal o f g r a i n b o u n d a r i e s .  They a l s o found t h a t  i n f i l t r a t i o n o f i r o n w i t h a copper - 4.5% i r o n l i q u i d  caused  l e s s e x p a n s i o n and a t t r i b u t e d t h e e f f e c t t o t h e reduced r a t e of s o l u t i o n o f i r o n i n t h e a l l o y e d  liquid.  B e r n e r et al. p o i n t e d o u t t h a t t h e f o l l o w i n g a d d i t i o n s t o t h e i r o n - c o p p e r system have been, found by o t h e r s t o reduce t h e amount o f e x p a n s i o n observed d u r i n g l i q u i d phase sintering  [12]:  c a r b o n , t i n , phosphorous,  t u n g s t e n and l e a d .  K r a n t z [27] a l s o performed l i q u i d phase s i n t e r i n g and i n f i l t r a t i o n experiments on Fe-Cu m i x t u r e s .  He o b s e r v e d  t h a t t h e a d d i t i o n o f 1.2% carbon t o 6% copper m i x t u r e s r e d u c e d t h e e x p a n s i o n ( a f t e r 30 m i n u t e s a t 1120°C) from 2.4% t o 0.2% (AL/Lo).  (AL/L ) 0  He noted t h a t t h e e x p a n s i o n was r a p i d and  completed i n t e n m i n u t e s .  He s u g g e s t e d t h a t t h e compacts  expanded by t h e l a t t i c e d i f f u s i o n o f copper i n t o i r o n and a l s o by. g r a i n boundary  diffusion.  He f u r t h e r h y p o t h e s i z e d  t h a t t h e e f f e c t o f carbon was t o reduce t h e r a t e o f g r a i n boundary  diffusion. Bockstiegel  [15] proposed t h a t i n Fe-Cu-C m i x t u r e s  the f o r m a t i o n o f an i r o n - c o p p e r - c a r b o n t e r n a r y immiscible with the copper-rich  alloy,  l i q u i d , increases the " s o l u t i o n -  p r e c i p i t a t i o n " o f i r o n t o such a degree t h a t d e n s i f i c a t i o n overshadows some o f t h e e x p a n s i o n .  30  1.5.6  Shortcomings o f P r e v i o u s Work Much o f the p r e v i o u s l y  r e p o r t e d work on s i n t e r i n g  i n the Fe-Cu system i s d i f f i c u l t t o i n t e r p r e t and has l e d t o a c o n f u s i o n o f t h e o r i e s , due t o s h o r t c o m i n g s i n e i t h e r experimental technique or i n the r e p o r t i n g For  example: a)  experiments early  In many were  expansion  result, copper  investigations  conducted, effects  c o n t e n t and  sometimes  poorly  size  and  iron  powders, which  have  distribution,  and  c) densities  of  investigation  used  Fe-Cu  effect  with  have not  isolate  an  carbon  (and,  w i t h o u t adequate  on  particle  particle  the  varied  of expansion most  size  shapes.  as-compacted  w i d e l y from within  consideration  sintering  as  particle  In a d d i t i o n ,  a wide  sometimes,  a  have  content  important e f f e c t  have  such  respect to  the  of  As  investigations  p r e s s u r e s , and  of  made t o  are often questionable.  specified.  specimens,  results  sintering  variables,  with  example,  a variety  to another  to the  of  in previous  powders w i t h  Compacting  investigation), importance  might  i s commonly  investigators  e f f o r t was  characterized For  long  later shrinkage effects.  the  used  composition.  sintering,  of  no  only  powder.particIe size,  Powders  been  and  from  interpretations  b)  in  of the r e s u l t s .  of  a  one  single their  experiments.  31  •d) a  The t h e r m a l  specified  Some  sintering  investigators  the  solid  (a  common  have  state  of compacts  temperature,  may  have  prior  i s commonly  "presintered"  to reaching  not described.  their  compacts i n  before performing the liquid-phase  routine  heated  history  them  in parts directly  manufacture) t o above  whereas  I084°C  from  experiments  others the  may  as-compacted  cond i t i o n . Even  where  vary  greatly  from  Thus  a specimen Cl2]  spent  copper  and  I I50°C.  a rate  three  minutes  incapable  above,  been  some  sintering  used  expansion  These  either  copper  powder  include:  heated  t o I 150°C  liquid  f o r only  temperature  was  in previous studies and c o n t r a c t i o n  investigators  variables, n o t been  t h e degree  mixtures, the size  to that  o f 5°C p e r  have  reached.  were  in the  apparently  failed  altogether.  Experimental have  to another.  contained  of the iron,  other than  kept  inadequately characterized  work.  relative  hence,  of heating  the melting point of  a specimen  Cl-O  Some d i l a t o m e t e r s  expansion  f)  have  between  In c o n t r a s t ,  of o b s e r v i n g both  observe  tioned  13 m i n u t e s  before the final  same s p e c i m e n ;  rates  t o , s a y , II50°C a t a r a t e  o f 26°C p e r m i n u t e s  e)  to  are specified,  one r e p o r t e d i n v e s t i g a t i o n  heated  minute  at  they  under  those  control  menor  in previous reported  of blending of the iron of the copper  the temperature  powder  and  particles  gradients in  32  the  specimen  density  after  dimensional can  during  have  compaction  changes  important  sintering,  liquid-phase  iron,  1.6  effects  sintering).  of  study  i n t h e Fe-Cu  b e e n made t o f o l l o w  relationships,  and t h e d e g r e e  the extent  specimen of  of these  variables  of liquid-phase  results.  of the progress  of  L~23H h a s a n y  structural have  changes been  of d i f f u s i o n  of c o n t i n u i t y  metaI I o g r a p h i c  Each  system  Frequently, assumptions  of  isotropy  on t h e p r o g r e s s  one p r e v i o u s  sintering  effort  supporting  (and t h e r e s u l t i n g  during  In o n l y  metallography. wetting  the homogeneity  and on t h e i n t e r p r e t a t i o n  g)  serious  sintering,  of the s o l i d  by  made  about:  of copper phase,  into without  evidence.  O b j e c t i v e s o f t h i s Work T h i s work was u n d e r t a k e n p r i m a r i l y  as an e f f o r t t o  overcome some o f t h e c o n f u s i o n w h i c h e x i s t s i n t h e l i t e r a t u r e c o n c e r n i n g t h e o r i g i n o f t h o s e d i m e n s i o n a l changes w h i c h o c c u r d u r i n g l i q u i d - p h a s e s i n t e r i n g o f i r o n - c o p p e r powder compacts.  By means o f s i n t e r i n g experiments  important v a r i a b l e s  i n which the  were under r e a s o n a b l e c o n t r o l , and w i t h  thorough s u p p o r t i n g m e t a l l o g r a p h y , i t was hoped t o be a b l e to:  a) i d e n t i f y t h e mechanisms r e s p o n s i b l e f o r b o t h  expansion  and s h r i n k a g e i n t h e system and, b) d i s t i n g u i s h t h e i n d i v i d u a l e f f e c t s , on s i n t e r i n g , o f such v a r i a b l e s  as powder p a r t i c l e  33  s i z e , amount o f copper, i n i t i a l d e n s i t y o f t h e compact and t h e sequence o f t h e r m a l p r o c e s s i n g p r i o r t o , and d u r i n g , sintering. I n a l l e x p e r i m e n t s , c l o s e a t t e n t i o n was p a i d t o the powder s i z e d i s t r i b u t i o n s , t h e degree o f m i x i n g o f t h e powders, t h e d i m e n s i o n a l  changes d u r i n g c l e a n i n g  (deoxidizing)  o f t h e compacts and t h e d e n s i t i e s o f compacts a t t h e s t a r t o f liquid-phase sintering.  The h e a t i n g r a t e through t h e m e l t i n g  p o i n t o f copper, and t h e t h e r m a l  h i s t o r i e s o f samples, were  d u p l i c a t e d as c l o s e l y as p o s s i b l e t o remove " h e a t i n g r a t e " effects..  The d i m e n s i o n a l  changes d u r i n g s i n t e r i n g were  measured c o n t i n u o u s l y w i t h a s e n s i t i v e d i l a t o m e t e r and t h e anisotropy of dimensional  changes i n t h e compacts d u r i n g  s i n t e r i n g <was; c l o s e l y m o n i t o r e d . M i c r o s t r u c t u r a l i n v e s t i g a t i o n s were used t o complement d i l a t o m e t r y i n d e t e r m i n i n g phase s i n t e r i n g .  t h e mechanisms  of l i q u i d -  Chapter 2  MATERIALS/ APPARATUS AND EXPERIMENTAL PROCEDURE  2.1  M e t a l Powders and Specimen P r e p a r a t i o n The two i r o n powders, one copper powder, and one  p r e a l l o y e d Fe-Cu powder d e s c r i b e d i n T a b l e I I were used i n the experiments.  A l l were produced  by a t o m i s a t i o n p r o c e s s e s .  T a b l e I I I c o n t a i n s t h e r e s u l t s o f c h e m i c a l a n a l y s e s on t h e a s - r e c e i v e d powers. The powders were s e p a r a t e d i n t o t h e e i g h t s i z e fractions  l i s t e d i n Table IV, using 'Tyler  'Rotap' machine.  1  s c r e e n s and a  Copper and i r o n powder f r a c t i o n s were t h e n  mixed a c c o r d i n g t o t h e w e i g h t p e r c e n t a g e s g i v e n i n T a b l e V. L i q u i d Carbowax 300 was added t o a l l t h e m i x t u r e s (Specimen Groups) e x c e p t PCM-3-1 and PM-2. - I t f u n c t i o n e d as b o t h a m i x i n g agent and l u b r i c a n t .  Carbowax 300 i s a p o l y e t h y l e n e  g l y c o l w i t h a f l a s h p o i n t o f 196°C and does n o t h y d r o l y z e . The p o w d e r - l u b r i c a n t m i x t u r e s were b l e n d e d i n a a P a t e r s o n K e l l y t w i n - s h e l l b l e n d e r f o r one hour. The c o m p o s i t i o n s o f t h e power m i x t u r e s f o r v a r i o u s Specimen Groups were c a l c u l a t e d 34  t o g i v e iron-copper weight  35  Table I I M e t a l Powders  Powder D e s i g n a t i o n  Supplier  L o t No.  Description  PM  Easton Metal Powders  RZ 365,746-3  Iron  CM  Alcan  Grade MD154 #2056  Copper  Quebec M e t a l Products  Atomet 28 64  Iron  Domtar A-178  Prealloyed "Fe-7 Cu"  ATO  PA  *  Domtar  *  C o u r t e s y o f Dr. R. A n g e r s , U n i v e r s i t y de L a v a l , Quebec.  36  Table I I I C o m p o s i t i o n o f M e t a l Powders  Element  Powder PM  Fe  99.28  Cu  T  CM 0. 001 99.35 NP  ATO 99.8 T  T  PA 92.3 6.85  0.01  0.04  0.07  0.07  0.01  0.08  0.005  0.012  C  0.10  Si  0.01  Mn  0.34  S  0.003  <0.001  P  0.006  0.017  NP  NP  Sn  NP  0.09  0.01  0.01  Zn  NP  0.008  NP  NP  Pb  NP  0.015  NP  NP  T = Trace  0. 001 NP  NP = Not Performed  37  T a b l e IV Powder S i z e F r a c t i o n s  Powder S i z e D e s i g n a t i o n  Mesh ("Tyler")  A  P a r t i c l e Diameter Microns (u ) m  105 t o 120  0  + 200  74 t o 105  1  -200  +230  63 t o  74  2  -230  + 27 0  53 t o  63  3  -270  + 325  45 t o  53  4  -325  + 400  37 t o  45  5  -400  + 500  25 t o  37  6  -500  UF  <25 See T a b l e V I  Table V Powder M i x t u r e s  used i n Compacts Component M a t e r i a l s  Particle  Specimen  Size  Group  Range  Designation PCM-A PCM-2-XX(or X) PCM 3-1 PCM-5-XX(or X) PCM-6* ATOCM-5* * PA-2-1 PCM-UF-2 PCM-2-100* PM-2* X = digit  Iron  Copper  PM  CM  Wt.%  Wt.  105 t o 120  76.50  53 t o 63  77.23  45 t o 53  78.0  25 t o 337  77.23  21.51 21.78 22.0 21.78 21.78 21.78 14.92 203.78 9.90  <25  77.23  25 t o 337 53 t o 63 53 t o 63  77.23 89.11  53 t o 63  100  See T a b l e V I  , nn  ;  Iron ATO Wt.  Fe-7Cu  Lubricant Carbowax  PA Wt.  ;  Wt. 1.99 0.99  77.23 84.11  0.99 0.99 0.99 0.99 0.99 0.99  (run designation) I n d i c a t e s t h a t t h e Specimen Group comprised a s i n g l e specimen. 00  39  r a t i o s o f 90/10, 78/22 and pure i r o n a f t e r  'dewaxing'  (removal  of t h e carbowax d u r i n g t h e c l e a n i n g o p e r a t i o n d e s c r i b e d below). I n each o f t h e m i x t u r e s , e x c e p t t h a t used f o r PCMUF-2,  t h e copper and i r o n powders were b o t h o f t h e same s i z e  fraction.  The s i z e s o f t h e powders i n PCM-UF-2 a r e l i s t e d  i n Table V I . S u i t a b l e w e i g h t s o f p o w d e r m i x t u r e s were compacted i n a s i n g l e - a c t i n g d i e t o y i e l d c y l i n d r i c a l specimens o f 0.5 i n c h e s d i a m e t e r by a p p r o x i m a t e l y  0.5 i n c h e s i n h e i g h t .  Specimen PCM-2-30 was p r e s s e d a t 180 k . s . i . ; a l l o t h e r s p e c i ments were compacted a t 60 k . s . i .  The dimensions and w e i g h t  o f each compact were measured t o a l l o w c a l c u l a t i o n s o f t h e compacted d e n s i t y  (p-'o).  A l l compacts were dewaxed and c l e a n e d o f o x i d e by h e a t i n g i n hydrogen i n a tube f u r n a c e , u s i n g t h e two s t a g e t h e r m a l c y c l e shown i n F i g u r e 9.  The t r e a t m e n t  was  designed  to achieve three o b j e c t i v e s : i) ii)  iii)  To r e m o v e o x y g e n  from  t h e compacts  To c a u s e e n o u g h s o l i d s t a t e s i n t e r i n g o f t h e p o w d e r s t o a l l o w t h e c o m p a c t s t o be d r i l l e d w i t h o u t c r a c k i n g , but not so much s i n t e r i n g t h a t l a t e r l i q u i d - p h a s e s i n t e r i n g w o u l d be a f f e c t e d a p p r e c i a b l y , and To r e m o v e a l l C a r b o w a x the reof .  and  residues  A f t e r c l e a n i n g , t h e w e i g h t s and d i m e n s i o n s o f t h e compacts were remeasured t o p e r m i t t h e c a l c u l a t i o n o f c l e a n e d  40  Table VI S i z e F r a c t i o n s o f Powders i n Specimen PCM-UF-2  Size 6  Powder Diameter .urn m <25  PM Q. "O  CM Q,  9.5  5  25 t o 37  9.7  4  37 t o 45  12.1  3  45 t o 53  11.5  2  53 t o 63  7.9  1  63 t o 74  13.1  0  74 t o 105  13.1  A  105 t o 120  10.0  <120  13.1  100.0  800  h  Time  F i g u r e 9.  Heating  (min)  cycle for cleaning.  (Hydrogen f l o w throughout c y c l e ) .  42  densities  ( P ) and the w e i g h t l o s s e s d u r i n g c l e a n i n g .  To  accommodate a thermocouple d u r i n g d i l a t o m e t r y , a h o l e  was  c  d r i l l e d i n each compact a c c o r d i n g t o F i g u r e  2.2  The  10.  Dilatometer  2.2.1  Description The d i l a t o m e t e r , w h i c h gave c o n t i n u o u s  measurements  of t h e l e n g t h o f a compact d u r i n g l i q u i d - p h a s e s i n t e r i n g , i s shown i n F i g u r e 11. supported was  I t c o n s i s t e d o f a s t e e l frame which  a t r a n s d u c e r w e l l above the powder compact w h i c h  being l i q u i d - p h a s e s i n t e r e d .  l a v a b l o c k p e d e s t a l and was i n s i d e a s i l i c a g l a s s tube.  The  compact r e s t e d on a  surrounded by an a l u m i n a The  sheath  t r a n s d u c e r produced an  e l e c t r i c a l o u t p u t p r o p o r t i o n a l t o the amount o f upward o r downward d i s p l a c e m e n t  o f an i n t e r n a l i r o n s u s c e p t o r .  The  s u s c e p t o r was  l i n k e d t o the top o f the compact by a s l e n d e r  alumina r o d .  S i l i c a d i s c s were used between t h e specimen  and the alumina r o d , and between t h e specimen and t h e l a v a block. The  compact was  heated by a c o n c e n t r i c i n d u c t i o n  c o i l s i t u a t e d o u t s i d e the s i l i c a g l a s s tube. o f the compact was  continuously monitored  by a  The  temperature  'centred  1  t u n g s t e n - r h e n i u m thermocouple w h i c h e n t e r e d t h e bottom o f the compact through was  the l a v a b l o c k p e d e s t a l .  Enough c l e a r a n c e  a l l o w e d between the t i p of the thermocouple and the top  43  F i g u r e 10.  D r i l l e d compact.  44  H  2  gas  Transducer  Water  cooled  Alumina  Silica  collar  rod  glass tube  Induction  coil  jsilica discs at both ends ot powder compact Alumina Lava  tube  block  Thermocouple  F i g u r e 11.  The d i l a t o m e t e r .  45  o f the h o l e d r i l l e d i n the compact so t h a t a l i n e a r c o n t r a c t i o n o f s e v e r a l p e r c e n t c o u l d o c c u r b e f o r e t h e specimen would come t o r e s t on the thermocouple. A w a t e r - c o o l i n g c o l l a r mounted on the t o p o f t h e s i l i c a g l a s s tube k e p t t h e t r a n s d u c e r near room t e m p e r a t u r e d u r i n g h e a t i n g o f t h e compacts.  The t r a n s d u c e r d i d n o t r e s t  on the water c o l l a r ; r a t h e r i t was h e l d i n p l a c e by a s e t screw i n t h e s t e e l frame t h r o u g h w h i c h i t p a s s e d .  The a l u m i n a  r o d s t o o d f r e e i n s i d e t h e d i l a t o m e t e r and t r a n s d u c e r and was h e l d v e r t i c a l by a s m a l l h o l e i n t h e w a t e r c o l l a r .  The  s u s c e p t o r and r o d e x e r t e d a l o a d on the top o f t h e compact equal to t h e i r weight only  (8 grams).  The t r a n s d u c e r o u t p u t was l i n e a r w i t h d e f l e c t i o n o f t h e s u s c e p t o r up t o 0.050" above o r below t h e ' n u l l p o i n t ' of t h e t r a n s d u c e r . The o u t p u t was connected t o a d i f f e r e n t i a l transformer i n d i c a t o r  ( a m p l i f i e r ) which converted  i t i n t o thousandths o f an i n c h d e f l e c t i o n o f the s u s c e p t o r , and d i s p l a y e d t h e amount on a VU meter. a l s o connected t o a c h a r t r e c o r d e r .  The a m p l i f e r  was  The v i s u a l o u t p u t o f  the a m p l i f i e r p r o v i d e d a check on the s t r i p c h a r t pen deflection. The thermocouple was connected t o a c o l d j u n c t i o n and thence t o the P h i l l i p s i n d u c t i o n - f u r n a c e c o n t r o l u n i t which c o n t a i n e d a thermocouple o u t p u t s t r i p c h a r t r e c o r d e r w i t h a 25 m.v.  full-scale deflection.  Independent d e t e r m i n a -  t i o n s o f t h e temperature a t t h e thermocouple were a l s o made  46  with a potentiometer  a c c u r a t e t o 0.01 m.v.  Control of the  power i n p u t t o t h e i n d u c t i o n c o i l was manual. Hydrogen was s u p p l i e d c o n t i n u o u s l y t h r o u g h o u t a l l runs.  I t was i n t r o d u c e d a t t h e t o p o f t h e t r a n s d u c e r i n  the d i l a t o m e t e r a t t h e r a t e o f a p p r o x i m a t e l y and a t a p p r o x i m a t e l y  20 p . s . i .  150 c u . f t . / h r  The hydrogen was d r i e d w i t h  " D r i e r i t e " and phosphorus p e n t o x i d e i n U-tubes between t h e s u p p l y and t h e d i l a t o m e t e r .  2.2.2  Advantages o f t h e D i l a t o m e t e r  Design  The d e s i g n o f t h e d i l a t o m e t e r and specimen was such as t o promote: i)  ii)  iii)  U n i f o r m i t y and symmetry o f h e a t i n g along the length,and in the plane perpendicular to the d i r e c t i o n of measurement of t h e compact. Rapid heating through the s e c t i o n and l e n g t h o f t h e Shallow temperature the compacts ( l a t e r  crosscompact.  gradients in verified).  The above a r e i m p o r t a n t c o n s i d e r a t i o n s because t h e changes i n d i m e n s i o n d u r i n g l i q u i d - p h a s e s i n t e r i n g a r e r a p i d and extensive. A f u r t h e r advantage o f t h e d i l a t o m e t e r was t h a t i t measured b o t h e x p a n s i o n and c o n t r a c t i o n , and d i d so w h i l e e x e r t i n g o n l y a s m a l l l o a d on t h e compacts ( e q u a l t o a p p r o x i m a t e l y 2/3 o f t h e w e i g h t o f a compact). the d i l a t o m e t e r were c o n t i n u o u s l y  A l s o t h e d a t a from  generated.  47  I n d u c t i o n h e a t i n g was  employed because i t o f f e r e d  f l e x i b i l i t y i n the c o n t r o l o f h e a t i n g c y c l e s and heated samples w i t h s h a l l o w temperature g r a d i e n t s .  the  I t also offered  the a b i l i t y t o c o o l specimens r a p i d l y from the s i n t e r i n g temperature.  2.3  D i l a t o m e t r i c Technique The  d i l a t o m e t e r t r a n s d u c e r was  c a l i b r a t e d , occasion-  a l l y , u s i n g a f e e l e r guage o f known t h i c k n e s s . of the p r o c e d u r e , w i t h o u t  Repetition  i n t e r v e n i n g adjustment o f  a m p l i f i e r , e s t a b l i s h e d t h a t the d i l a t o m e t e r was w i t h i n 0.00025" (or a p p r o x i m a t e l y  0.05%  the  accurate  to  of the l e n g t h of  the compacts). A c o r r e c t i o n f o r the e x p a n s i o n and c o n t r a c t i o n of the l a v a b l o c k , was dilatometer. s t e e l block  made t o the c u r v e s f o r each r u n i n the  Simulated  runs were performed u s i n g a  'cored  1  ( i n s t e a d o f a compact) through w h i c h the a l u m i n a  r o d passed t o the l a v a b l o c k p e d e s t a l .  Curves were g e n e r a t e d  w h i c h gave the p r e c i s e changes i n d i m e n s i o n of t h e l a v a b l o c k . The  r e s u l t i n g c u r v e s (one f o r each t y p e o f h e a t i n g  were s u b t r a c t e d from the s u r v e s  cycle)  f o r s i n t e r i n g runs, to give  the t r u e changes i n dimensions o f the compacts. The measurement o f the l e n g t h of the compacts a f t e r c l e a n i n g s e r v e d as the b a s i s f o r c o n v e r t i n g  dilatometer  d a t a t o %(AL/Lo) ( i . e . the change of l e n g t h r e l a t i v e t o the  48  cleaned  length).  A t t h e end o f each r u n measurements were  made o f t h e samples u s i n g c a l i p e r s .  Because t h e compacts  c o o l e d i n t h e apparatus w i t h t h e d i l a t o m e t e r o p e r a t i n g , t h e measured change i n l e n g t h d u r i n g a r u n c o u l d be compared w i t h t h e change i n l e n g t h as r e c o r d e d  by t h e d i l a t o m e t e r .  Four b a s i c h e a t i n g c y c l e s were used f o r d i l a t o m e t e r runs.  They a r e d e s c r i b e d i n F i g u r e s 12 t h r o u g h 15.  The  c y c l e w h i c h i n c l u d e d one hour a t 1000°C r e s u l t e d i n e x t e n s i v e s o l i d s t a t e s i n t e r i n g o f compacts and was known as ' p r e sintering  corporated constant  (see F i g u r e 15).  1  A l l but the 'rapid' cycle i n -  two h o l d i n g stages where t h e t e m p e r a t u r e was h e l d  f o r a few m i n u t e s , o r more, t o reduce t e m p e r a t u r e  g r a d i e n t s i n t h e compacts. I t was n o t always p o s s i b l e t o r e p r o d u c e a g i v e n heating cycle exactly.  During the f i r s t stage o f heating  (from 20°C t o 700°C), i t was n o t p o s s i b l e t o reduce t h e power i n p u t t o t h e c o i l below a c e r t a i n l e v e l , and some compacts reached 700°C e a r l i e r than o t h e r s .  However, t h e  h o l d i n g t i m e s and h e a t i n g r a t e s were reproduced as c l o s e l y as p o s s i b l e a t h i g h e r t e m p e r a t u r e s .  Thus, some samples  r e a c h e d t h e m e l t i n g p o i n t o f copper a t s h o r t e r t o t a l t i m e s than o t h e r s .  I f a sample r e a c h e d t h e m e l t i n g p o i n t w i t h i n  60 seconds o f t h e time t h a t temperature was reached i n one of t h e f o u r t y p i c a l h e a t i n g c y c l e s ( F i g u r e s 12 t o 1 5 ) , i t was c o n s i d e r e d  t o have been heated w i t h t h a t h e a t i n g c y c l e .  Figure 12.  'Normal  1  heating  cycle.  F i g u r e 13.  'Rapid  1  heating  cycle.  F i g u r e 14.  'Slow' h e a t i n g  cycle*  Time F i g u r e 15.  (min)  'Presintering' heating  cycle.  53  Because any two compacts, heated w i t h a g i v e n c y c l e , e x p e r i enced e s s e n t i a l l y i d e n t i c a l h o l d i n g t i m e s and h e a t i n g r a t e s above 800°C, t h e (AL/L ) v e r s u s t i m e c u r v e s f o r t h e two runs 0  c o u l d be compared above the m e l t i n g temperature w i t h c o n f i d e n c e . The purposes f o r w h i c h the v a r i o u s powder were used a r e d e s c r i b e d i n T a b l e V I I .  specimens  Some o f the d i l a t o m e t e r  runs were s i m p l y r e p r o d u c t i o n s o f o t h e r s f o r e s s e n t i a l l y i d e n t i c a l specimens.  Where good r e p r o d u c i b i l i t y was  indicated,  a s i n g l e r e p r e s e n t a t i v e d i l a t o m e t e r p l o t i s p r e s e n t e d i n the thesis.  2.4  Other E x p e r i m e n t a l P r o c e d u r e s Other e x p e r i m e n t a l work comprised:  metallography,  scanning e l e c t r o n microscopy, e l e c t r o n microprobe  analysis  and c h e m i c a l a n a l y s i s o f t h e m i x t u r e s (Specimen Groups) and compacts g e n e r a t e d i n t h e e x p e r i m e n t s .  Cleaning tests  and  m i x i n g t e s t s were a l s o performed, as i n d i c a t e d i n T a b l e V I I . Cleaning t e s t s c o n s i s t e d of performing the c l e a n i n g p r o c e d u r e i n one hour s t a g e s and w e i g h i n g the compacts between s t a g e s . w e i g h t l o s s was  The o b j e c t was t o d e t e r m i n e when most o f t h e complete and how e f f e c t i v e was  the oxygen  removal. Mixing t e s t s c o n s i s t e d simply of o b t a i n i n g chemical a n a l y s e s on the t o p and bottom h a l v e s o f compacts w h i c h had  Table V I I D i s p o s i t i o n o f Samples  Sample  Dilatometry Run Performed  AL/Lo Curve Produced  Cleaning Test  Mixing Test (chem. a n a l y s i s )  PCM-2-3 PCM-2-4 PCM-2-5 PCM-2-6 PCM-2-10 PCM-2-12 PCM-2-13 PCM-2-14 PCM-2-15 PCM-2-17 PCM-2-18 PCM-2-19 PCM-2-20 PCM-2-21 PCM-2-22 PCM-2-23 PCM-2-24 PCM-2-25 PCM-5-6 PCM-5-7 PCM-5-9 PCM-5-12 PCM-5-13  N N Y Y Y Y Y N Y Y Y Y Y Y Y Y Y Y Y N N Y Y  N N N N Y N N N N N Y Y Y N Y Y Y Y Y N N Y Y  N Y N N N N N N N N N N N N N N N N N Y N N N  Y N N N N N N N Y, N N N N N N N Y N N N Y N N  Y = y e s , N = no  Metallography  Other C h e m i c a l Analysis  N Y Y Y N N. •. N Y N Y Y N Y Y Y N N N N N N N Y CONTINUED  N N N N N N N N N N N N N N N N N N N N N N N  T a b l e V I I (Continued)  Sample PM-2 PCM-3-1 PCM-6 PCM-A PCM-UF-2 PCM-2-30 PCM-2-100 PA-2-1 ATOCM-5  Dilatometry Run Performed  A L / L o Curve Produced  Cleaning Test  Y N Y Y Y Y Y Y Y  Y N Y Y Y Y Y Y Y  N Y N N N N N N N  Mixing Test (chem. a n a l y s i s ) N N N N N N N N N  Metallography  Other Chemical Analysis  N N Y Y N N Y Y N  N N Y Y N N Y Y Y  Cn  56  been c l e a n e d but n o t l i q u i d - p h a s e s i n t e r e d .  Comparison o f  the r e s u l t s o f c h e m i c a l a n a l y s e s i n d i c a t e d t h e degree o f homogeneity o f t h e m i x i n g i n t h e compacts. P r i o r t o s e c t i o n i n g f o r m e t a l l o g r a p h i c work, t h e compacts were immersed i n an epoxy r e s i n under a vacuum. The r e s i n was  "drawn" i n t o , and f i l l e d , t h e i n t e r c o n n e c t e d  pores i n t h e compact.  A f t e r t h e epoxy had hardened t h e  samples were p o l i s h e d and t h e epoxy " f i l l e r " m a i n t a i n e d i n t e g r i t y of the interconnected  pores.  the  Chapter  3  OBSERVATIONS AND RESULTS  3.1  Observations: 3.1.1  B l e n d i n g , Compacting and C l e a n i n g  B l e n d i n g and Compacting  F i g u r e 16 i s a photomicrograph  o f a p r e s s e d and  cleaned  sample from Specimen Group PCM-2-XX.  E x c e l l e n t mixing of the  i r o n and copper powders i s e v i d e n t .  T y p i c a l l y , never more  than f o u r copper p a r t i c l e s were found t o be " n e a r e s t n e i g h b o u r s " i n the s e c t i o n s examined; i . e . t h e r e was c l u s t e r i n g o f the copper p a r t i c l e s .  minimal  Metallographic studies  o f o t h e r samples and Specimen Groups (PCM-6, PCM-A, PCM-5-XX and ATOCM-5) i n d i c a t e d a s i m i l a r l y h i g h degree of m i x i n g . Mixing tests  ( c h e m i c a l a n a l y s e s ) i n d i c a t e d t h a t the  v a r i a t i o n o f copper c o n t e n t from compact t o compact, and a l o n g the l e n g t h o f i n d i v i d u a l compacts o f t h e same Specimen Groups, was  l e s s than t h r e e per c e n t o f the amount o f copper  present. T a b l e V I I I shows t h a t f o r a g i v e n c o m p o s i t i o n o f powder mixture  ( c o n t a i n i n g l u b r i c a n t ) , the compacted d e n s i t i e s were  lower f o r f i n e r powders.  The v a r i a t i o n o f compacted d e n s i t y 57  58  F i g u r e 16.  S e c t i o n o f compact PCM-2-14 a f t e r c l e a n i n g . lOOx. The v o i d s appear b l a c k , the copper i s t h e l i g h t e s t c o n s t i t u e n t o b s e r v e d . The g r e y a r e a s are i r o n . ( N i t a l etch)  59  Table V I I I Average D e n s i t y o f Fe-2 2Cu-lG.afbow/ax Compacts P r e s s e d a t 60 k . s . i .  Specimen Group  Pressed Density Po (gm/cc)  Powder S i z e u (diam.)  Clean Density Pc (% o f theoretical)  m  PCM-A  6.61  105 t o 120  68.7  PCM-2-XX  6.34  53 t o 63  70.7  PCM-5-XX  6.21  25 27 25 t o 37  70.3  PCM-6  6.17  <25  68.7  60  f o r samples i n a g i v e n Specimen Group was  l e s s than  0.8%.  Sample PCM-3-1 was o f a powder s i z e i n t e r m e d i a t e between t h o s e of Specimen Groups PCM-2-XX and PCM-5-XX but c o n t a i n e d  no  Carbowax.  gm/cc  PCM-3-1 compacted t o a d e n s i t y o f o n l y 6.04  i n d i c a t i n g t h a t t h e use o f a l u b r i c a n t l e d t o h i g h e r compacted d e n s i t i e s f o r a g i v e n compacting  3.1.2  pressure.  Cleaning  T a b l e IX shows i t h ^ complete r e s u l t s f o r t h e compacted d e n s i t i e s , c l e a n e d d e n s i t i e s and changes i n w e i g h t , l e n g t h and d i a m e t e r o f compacts w h i c h were c l e a n e d . A l l compacts (except PM-2  w h i c h was pure i r o n powder)  expanded a p p r e c i a b l y as a r e s u l t o f c l e a n i n g .  The  was n o t a s s o c i a t e d w i t h the p r e s e n c e of l u b r i c a n t .  expansion The  specimen PCM-3-1, which d i d not c o n t a i n Carbowax 300, a l s o expanded d u r i n g c l e a n i n g . i n PM-2  Because no e x p a n s i o n was  observed  which d i d n o t c o n t a i n copper; whereas a l l samples  c o n t a i n i n g copper expanded, t h e e x p a n s i o n i s a s s o c i a t e d w i t h the presence o f copper. was  Moreover, the amount o f e x p a n s i o n  c l o s e l y r e l a t e d t o t h e amount o f copper powder i n t h e  mixtures. The compacts d i d n o t expand i s o t r o p i c a l l y d u r i n g c l e a n ing.  The r a t i o o f t h e e x p a n s i o n i n l e n g t h t o t h a t i n t h e  d i a m e t e r ( A L % / A D %) ranged from 1.44 t o 2.48 f o r d i f f e r e n t c c samples (see T a b l e I X ) . The more f r e q u e n t l y used specimens,  T a b l e IX Compacting and C l e a n i n g Sample Number  Compacting Pressure k. s. £ ; 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60  PCM-2-3 PCM-2-4 PCM-2-5 PCM-2-6 PCM-2-10 PCM-2-12 PCM-2-13 PCM-2-14 PCM-2-15 PCM-2-17 PCM-2-18 PCM-2-19 PCM-2-20 PCM-2-21 PCM-2-22 PCM-2-23 PCM-2-24 PCM-2-25 Average  —  Cleaned E x p a n s i o n i n Expansion i n Cleaned Compacted Loss i n D e n s i t y , % (AL c %/AD c%) Density, Weight Density Length Diameter t h e oretical* AL % (cleaning) AD % Po c c c p  gm/cc 6. 27 6.28 6.32 6.34 6.29 6.33 6.28 6.33 6.35 6.26 6.35 6.34 - 6.33 6.44 6.41 6.42 6.37 6.41 6.34  %  %  1.39 1.46 1.34 1.35 1.36 1.61 1.40 1.35 1.32 1.38 1.37 1.35 1.37 1.38 1.35 1.42 1.41 1.39  2.44 2.36 1.98 1.98 2.28 2.74 2.59 2.36 2.44 2.23 2.28 2.13 2.28 2.28 2.28 2.23 2.28 2.28 2.34  1.38 ND = n o t done  t h e o r e t i c a l d e n s i t y based on:  **  t o t a l l o s s , see T a b l e X  7.87 8.11 7.97 8.09  a *o  3.50 3.50 3.33 3.33 4.27 4.15 3.94 4.37 4.28 5. 00 4.95 5.01 4.09 4. 87 4.35 4.09 4337 4.11 4.21  %  gm/cc 5.70 5.71 5.74 5.84 5.70 5.67 5.66 5.70 5.73 5.62 5.70 5.71 5.74 5.79 5.79 5. 81 5.75 5. 80 5.73  70.3 70.4 70.8 72.0 70.3 69.9 69.8 70.3 70.6 69.3 70.3 70.4 70.8 71.4 71.4 71.6 70.9 71.5 70.6 CONTINUED  gm/cc gm/cc gm/cc gm/cc  f o r pure i r o n f o r 78% F e , 22% Cu m i x t u r e f o r 90% F e , 10% Cu m i x t u r e f o r PA-2-1 m i x t u r e  1.44 1.48 1.68 1.68 1. 87 1.51 1. 52 1.85 1.75 2.24 2.17 2.35 1.79 2.13 1.91 1. 83 1.98 1.80 1.80  T a b l e IX (Continued) Sample Number . PCM-5-6 PCM-5-7 PCM-5-9 PCM-5-12 PCM-5-13 Average PM-2 PCM-3-1 PCM-6 PCM-A PCM-UF-2 PCM-2-30 PCM-2-100 PA-2-1 , ATOCM-5  Compacting Compacted Density Pressure Po  k.s.i. 60 60 60 60 60  gm/cc 6.25 6.19 6.21 6.22 6.18  Cleaned L o s s i n E x p a n s i o n i n Expansion i n Cleaned Weight Density, Density, % Length Diameter (cleaning) AL % AD % theoretical c c c o 'o % &% " ? % gm/cc 1.47 .. 1.67 3. 80 5.76 71.0 1.45** 1.98 3.82 5.63 69.4 1.48 ND ND NND 70.8 1.52 3.35 5.74 1.51 70.3 1.52 3.35 5.70 1.65  (AL %/AD %) c  p  2.27 1.93 2.20 2.20  —  6.21  1. 51  1.67  3.58  5.71  70.3  2.15  60 60 60 60 60 180 60 60 60  5.95 6.04 6.17 6.61 6.46 7.43 6.21 6.36 6.28  0.35 0. 40** 1.68 2. 06 1. 51 1.11 1.16 1.36 1.19  0 1.98 1.52 3.04 1.94 1.98 1.52 1.75 1.52  0.13 3.78 2.60 5. 86 3.65 3.71 2.76 3.02 3.77  5.92 5.57 5.75 5.75 5.90 6.81 5.79 5. 88 5.82  75.2 68.7 68.7 68.7 72.7 84.0 72.7 72.7 71. 8  1.71 1.92 1.88 1.87 1. 82 1.73 2.48  1  c  63  from Groups PCM-2-XX and PCM-5-XX had average r a t i o s o f 1.8 and 2.2 r e s p e c t i v e l y .  (AL %/AD %) C  C  Each r a t i o i s t h e r e s u l t  of f o u r measurements w h i c h were a c c u r a t e t o 0.10% o f t h e sample l e n g t h .  Thus, a r a t i o o f ( A L % / A D %) w h i c h i s r e p o r t e d o c  as 2.00 c o u l d l i e between 1.65 and 2.45 due t o t h e i n a c c u r a c y o f t h e measurement t e c h n i q u e .  Even w i t h i n t h i s  limitation  however, t h e r e s u l t s i n d i c a t e g r e a t e r a n i s o t r o p y o f e x p a n s i o n i n t h e f i n e r powders. Although  l e n g t h and d i a m e t e r expansions* were unequal  f o r a l l Fe-Cu compacts, i t s h o u l d be noted t h a t no shape d i s t o r t i o n occurred during cleaning.  A f t e r cleaning, the  d i a m e t e r and l e n g t h o f a g i v e n compact were u n i f o r m w i t h i n 0.001 i n c h e s . Weight l o s s e s d u r i n g c l e a n i n g r e s u l t e d from t h e removal of Carbowax by v o l a t i l i z a t i o n and from t h e r e d u c t i o n o f o x i d e s on t h e m e t a l powder p a r t i c l e s .  The r e s u l t s i n T a b l e I X were  consistent with expectations; i . e . a)  Samples  PM-2 a n d PCM-3--I- c o n t a i n e d  Carbowax; mately b)  Samples  their  0.4$ w e r e o f Group  % o f Carbowax, were  weight  due t o o x i d e PCM-2-XX  and t h e i r  accordingly  variations  losses  of  no approxi-  reduction.  contained weight  approximately  I wt.  losses 1.4$.  are a t t r i b u t e d mainly t o  The  64  non-uniformity the c)  PCM-A  originally  compact  PCM-6  e)  original than  Because  with  compacts  except  oxide  (observed).  very  and s a m p l e  fine  contents  i n Group  Carbowax,  out of the  PCM-5-XX  from  i t lost  other  70.5%  2%  powders,  of which  during  e x h i b i t e d cleaned of theoretical  in the special  (pressed  high  m o r e o f i t s \% , C a r b o w a x  specimens  ± 2.5%  were  PCM-2-XX ,  PCM-2-30 was comp ao^e'd r a t ^a  pressure, than  pressing  o f Group  w e r e made  higher  contained  was s q u e e z e d  during  Specimens  the  of Carbowax  powders.  some o f w h i c h  d)  of mixing  cases  pressing. A l l d e n s i t i e s of solid  density,  o f PCM-2-30  a t 180 k . s . i . ) a n d PM-2  (pure  i ron) .  The  r e s u l t s o f c l e a n i n g t e s t s on samples which con-  t a i n e d 1% Carbowax (PCM-5-7 and PCM-2-4) and one w h i c h cont a i n e d no Carbowax (PCM-3tl) a r e g i v e n i n T a b l e X.  The d a t a  i n d i c a t e d t h a t a l l t h e Carbowax and most o f t h e oxygen i n the samples was l o s t i n t h e f i r s t hour o f c l e a n i n g a t 60 0°C. The  r e s u l t s o f c l e a n i n g a t 7 00°C f o r l o n g e r times t h a n  used i n t h e s t a n d a r d p r o c e d u r e was an almost n e g l i g i b l e amount o f a d d i t i o n a l w e i g h t l o s s  (0.01%).  those  65  Table X Weight Loss D u r i n g C l e a n i n g  Weight l o s s a f t e r 1 hour a t 600°C  Total cumulative loss after 1 hr. a t 600°C & 2 h r s . a t 700°C  Total cumulative weight l o s s a f t e r 1 h r . a t 600°C, 3 h r s . a t 700°C  PCM-5-7  1.25%  1.44%  1.45%  PCM-2-4  1.30%  1.40%  N/P  PCM-3-1  0.31%  0.39%  0.40%  Sample  N/P .= n o t performed  66  3.2  Changes i n Weight and Dimensions D u r i n g  Dilatometry  T a b l e XI c o n t a i n s d a t a showing the t o t a l changes i n dimensions o f samples heated f i g u r e s are  Three  recorded: i)  ii)  iii)  The  i n the d i l a t o m e t e r .  %  AL  S M  ,  the change in measured with  l e n g t h as calipers.  % AD^^,  t h e c h a n g e i n d i a m e t e r as measured w i t h c a l i p e r s .  % Al_2p,  the change in length by t h e dilatometer.  recorded  changes were c a l c u l a t e d as a p e r c e n t a g e of t h e a p p r o p r i a t e  d i m e n s i o n o f t h e sample a f t e r c l e a n i n g . A s i n g l e c a l i p e r measurement was  a c c u r a t e t o ±0.0005"  o r ±0.10% o f t h e sample l e n g t h (or d i a m e t e r ) .  Since % ALg  M  and % AD_„ SM are d i f f e r e n c e s between two measurements.' ±0.20% e r r o r was  p o s s i b l e due t o measuring u n c e r t a i n t y .  meter was  a c c u r a t e t o ±0.05% o f the sample l e n g t h .  the disagreement between % A L g  M  and % A L g  D  The  dilato-  Thus  f o r a s i n g l e run  c o u l d have been as h i g h as ±0.25% due t o t h e u n c e r t a i n t y o f the measuring t e c h n i q u e a l o n e .  F o r t h i s r e a s o n , an agreement  between % AL^„ SM and % A LSD', f o r a s i n• g l e r u n ,' o f b e t t e r t h a n OTN  0.50%  was  t o 0.75%  c o n s i d e r e d t o be a c c e p t a b l e . were a l s o c o n s i d e r e d r e a s o n a b l e  D i f f e r e n c e of i n those  0.50%  cases  where a compact might have shrunk s u f f i c i e n t l y t o come t o r e s t on t h e thermocouple d u r i n g t h e c o o l i n g s t a g e a t t h e o f the r u n .  end  T h i s c o u l d cause a sample t o l i f t o f f the l a v a  67  b l o c k base.  I f the i n t e r f e r e n c e w i t h sample s h r i n k a g e  by  t h e thermocouple o c c u r r e d , t h e e f f e c t would be c o n f i n e d t o the c o o l i n g s t a g e of the r u n  ( a f t e r the power was  cut o f f ) ;  i . e . , the d i l a t o m e t e r curve would not be a f f e c t e d up t o the p o i n t where h e a t i n g o f the sample was The d i f f e r e n c e between %  terminated.  AD.,.,  and %  SM  f o r a given ^  AL .. 0  SM  sample c o u l d have been as l a r g e as ±0.40% (even i f the sample shrank i s o t r o p i c a l l y ) due observed  t o measuring u n c e r t a i n t y .  The  d i f f e r e n c e s were g r e a t e r than ±0.40% f o r a p p r o x i -  m a t e l y t w o - t h i r d s o f the r u n s ; i . e . the s h r i n k a g e g e n e r a l l y not i s o t r o p i c .  was  About one o u t o f t h r e e samples  shrank more i n the d i a m e t e r  than i n the l e n g t h , w h i l e the  o t h e r s showed more s h r i n k a g e i n the l e n g t h t h a n i n t h e Approximately i n the d i a m e t e r ;  diameter.  h a l f o f the samples e x h i b i t e d a t a p e r  however, the d i f f e r e n c e between t h e l a r g e s t  and s m a l l e s t d i a m e t e r measured i n a sample was o f the average d i a m e t e r .  l e s s than  A l l the samples w h i c h had  3%  tapers  were l a r g e r a t the bottom,, w i t h the one e x c e p t i o n o f PCM-UF-2. None o f the samples i n w h i c h copper remained s o l i d , d u r i n g the whole r u n , e x h i b i t e d any s i g n i f i c a n t t a p e r i n t h e  diameter.  I t i s t h e r e f o r e p r o b a b l e t h a t the t a p e r i n g r e s u l t e d from sagging o f the compacts, due t o t h e i r w e i g h t (plus t h a t o f t h e t r a n s d u c e r c o r e ) , i n the p r e s e n c e o f a l i q u i d phase. A l l samples l o s t w e i g h t d u r i n g s i n t e r i n g i n t h e dilatometer  (see T a b l e X I ) .  Comparison o f Runs PCM-2-12  Table XI T o t a l Change i n Dimensions and Weight During D i l a t o m e t r y Specimen (Run) PCM-2-12 PCM-2-13 PCM-2-21 PCM-2-18 PCM-2-17 PCM-2-22 PCM-2-20 PCM-A PCM-6 PCM-UF-2 PCM-5-6 PCM-2-10 PCM-2-19 PCM-5-13 PCM-5-12 PCM-2-23 PCM-2-24 PCM-2-25 PCM-2-30 PCM-2-100 PA-2-1 ATOCM-5 PM-2  Melted  N N Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y  1 8SM (calipers) A  SM (calipers) %  A L  %  %  -0. 96 -0. 89 -1.15 -1.34 -0.7 5 -0.45 -2.31 -1.03 -6.37 -1.94 -5.54 -2.98 -3.17 -6.30 -6. 00 -2.75 -1.04 -2.23 + 0.67 + 0.08 -3.44 -3.77* -0.38  -0.82 -1.49 -2.iZ6 -2.22 -1.34 -0.63 -2.82 -2.48 -5.74 -2.33 -5.45 -2.32 -3.00 -6.16 -5.57 -3.02 -1.68 -2.39 -0. 81 -0.40 -3.99 -5.31* -0.47  O x i d i z e d a t end o f r u n  SD dilatometer %  A L  O  --2.38 —  -S0998 -S2S83 -T2.41  -6.05 -2.61 -5.33 -3.00 -2.82 -5.86 -5.18 -2.82 -1.86 -2.29 -0.38 -0.68 -3. 85 -5.01* -0.54  Y =  Measuring method showing most shrinkage Calipers  Dilatometer  —  —  —  —  —  —  —  Y  — — —  Y — —  —  Y Y —  Y Y  Y  —  —  Y  Y Y Y Y —  Y Y —  Y Y —  — — — —  Y — —  Y — —  Y  yes 00  T a b l e X I (Continued) Specimen (Run) PCM-2-12 PCM-2-13 PCM-2-21 PCM-2-18 PCM-2-17 PCM-2-22 PCM-2-20 PCM-A PCM-6 PCM-UF-2 PCM-5-6 PCM-2-10 PCM-2-19 PCM-5-13 PCM-5-12 PCM-2-23 PCM-2-24 PCM-2-25 PCM-2-30 PCM-2-100 PA-2-1 ATOCM-5 . PM-2  %AL  -%AL SM ° SD fl  %AD -%AL " SM ° SD aJj  %  Q. "O  --  ----  —  -+ 0.16 —  + 0.35 • + 0.01 -0.07 + 0.31 + 0.28 -0.12 +0.68 -0.18 -0.30 -0.39 -0.20 + 0.18 • -0.10 -0.43 +0 .28 -0.14 -0.30* + 0.07  + 0.52 + 0.52 +1.38 -0.32 +0.67 -0.21 + 0.02 -0.35 -0.44 -0.82 +0.07 +0.82 +0.06 +1.05 +0.76 + 0.41 +1.54* -0.09  Sintered density,.p gm/cc 5.84 5.85 6.11 5.98 5.77 5.75 6.20 6.02 6.93 6.26 6.79 6.17 6.26 6.89 6.85 6.30 5.97 6.19 6.74 5.78 6.56 — —  g  Weight l o s s %AW Q. s "O 0.09 0.14 0.11 0.18 0.19 0.24 0.42 0.42 0.61 0.47 0.64 0.54 0.58 0.51 0.54 0.53 0.41 0.44 0.45 0.76 0.41 -0.20* 0.21  70  t h r o u g h PCM-2-20 i n d i c a t e s t h a t t h e w e i g h t l o s s e s i n c r e a s e d w i t h l o n g e r s i n t e r i n g times i n t h e d i l a t o m e t e r , r e a c h i n g a l e v e l of approximately hours.  0.40% t o 0.60% f o r runs o f up t o two  However, about 0.15 t o 0.20% change i n w e i g h t  a f t e r s h o r t times  occurred  ( i . e . b e f o r e m e l t i n g , see T a b l e X I ; Runs  PCM-2-12 and PCM-2-13).  I t i s l i k e l y t h a t much o f t h e e a r l y  w e i g h t l o s s was due t o r e d u c t i o n o f o x i d e s 700°C) i n t h e compacts.  ( s t a b l e below  As f u r t h e r e v i d e n c e o f t h a t , t h e  pure i r o n specimen, PM-2, l o s t 0.2% w e i g h t a f t e r 18 m i n u t e s of t h e normal h e a t i n g c y c l e . Of t h e 0.2 t o 0.4% w e i g h t l o s s a f t e r m e l t i n g , some was due t o t h e e v a p o r a t i o n o f copper o u t o f t h e compacts. Copper was o b s e r v e d t o have condensed on t h e s i l i c a d i s c s and the a l u m i n a s h e a t h i n t h e d i l a t o m e t e r . analyses  However, c h e m i c a l  i n d i c a t e d t h a t n o t more t h a n 0.2% w e i g h t l o s s  r e s u l t e d from copper l o s s .  The remainder o f t h e w e i g h t l o s s  up t o 0.2% i s c o n s i d e r e d t o have been due t o l o s s o f oxygen from t h e compacts d u r i n g s i n t e r i n g above t h e m e l t i n g p o i n t o f copper. The  f i g u r e s f o r w e i g h t l o s s and d i m e n s i o n a l  changes  f o r t h e r u n ATOCM-5 s h o u l d n o t be compared w i t h o t h e r samples. The hydrogen f l o w f a i l e d a t t h e end o f t h e r u n , w h i l e t h e sample was b e i n g cooled.to room t e m p e r a t u r e .  As a r e s u l t ,  t h e sample o x i d i z e d t o a c o n s i d e r a b l e e x t e n t , and expanded. The  d i l a t o m e t e r d a t a , however, were u s e f u l because t h e hydrogen  supply d i d not f a i l u n t i l the c o o l i n g stage.  71 3.3  D i l a t o m e t r i c Data f o r a Pure I r o n Compact The  c o r r e c t e d d i l a t o m e t e r p l o t f o r the pure i r o n  compact, PM-2,  i s r e p r o d u c e d i n F i g u r e 17.  The  "normal"  h e a t i n g c y c l e used f o r t h i s specimen i s shown i n F i g u r e A t no s t a g e was  any  12.  l i q u i d phase formed.  I n common w i t h a l l d i l a t o m e t e r p l o t s i n t h i s work, F i g u r e 17 p r e s e n t s  the p e r c e n t a g e change i n l e n g t h of  compact ( r e l a t i v e t o i t s a s - c l e a n e d a f t e r w h i c h h e a t was dilatometer.  length) versus  the  the time  f i r s t a p p l i e d t o t h e specimen i n t h e  F o r the sake of c l a r i t y , the f i n a l p o r t i o n  of the e x p e r i m e n t a l  d i l a t o m e t e r p l o t s , w h i c h showed t h e  s h r i n k a g e o f specimens when h e a t i n g c e a s e d , has been o m i t t e d from t h e curves p r e s e n t e d  i n t h i s work.  W h i l e the compact was J i n F i g u r e 17)  b e i n g h e a t e d t o 500°C ( p o i n t  a r a p i d i n c r e a s e i n l e n g t h o c c u r r e d due  thermal expansion.  The  to  amount of e x p a n s i o n a t 500°C i s  c l o s e l y comparable t o what would be p r e d i c t e d f o r f u l l y dense pure i r o n , based on p u b l i s h e d t h e r m a l  expansion  coefficients. Above about 500°C, s o l i d - s t a t e s i n t e r i n g became r e l a t i v e l y r a p i d i n compacts of a p p r o x i m a t e l y powder.  55y  m  iron  The marked d e c r e a s e i n the s l o p e of the d i l a t o m e t e r  p l o t thus r e f l e c t e d the m o d i f y i n g s h r i n k a g e on t h e r m a l e x p a n s i o n .  i n f l u e n c e of s i n t e r i n g A 'net  o b s e r v e d between 500°C and 750°C.  1  expansion  was  Between p o i n t s K and  L  F i g u r e 17.  D i l a t o m e t e r p l o t f o r PM-2; a pure i r o n specimen heated w i t h a normal c y c l e .  73  (see F i g u r e 1 7 ) , t h e t e m p e r a t u r e was h e l d c o n s t a n t a t 750°C for  approximately  t h r e e minutes d u r i n g w h i c h time  sintering  s h r i n k a g e c o n t i n u e d , and a s m a l l 'net' c o n t r a c t i o n was observed. Between 750°C and a p p r o x i m a t e l y  900°C ( p o i n t M,  F i g u r e 17) t h e a t o y t r a n s f o r m a t i o n o c c u r r e d i n t h e lowcarbon i r o n , and t h e d i l a t o m e t e r p l o t r e f l e c t e d t h e change from a h i g h e r t o lower t h e r m a l e x p a n s i o n  coefficient.  h e a t i n g t o 1000°C ( p o i n t N, F i g u r e 17) produced in  the y - i r o n .  Further  expansion  Because s o l i d s t a t e s i n t e r i n g a t low tempera-  t u r e s i n t h e y phase i s i n t r i n s i c a l l y slow  (associated with  a low s e l f - d i f f u s i o n c o e f f i c i e n t ) , l i t t l e s i n t e r i n g occurred simultaneously i n that region.  shrinkage  F o r t h e same r e a s o n ,  h o l d i n g t h e specimen a t 1000°C (between p o i n t s N and P, F i g u r e 17) produced l i t t l e d i m e n s i o n a l  change.  F u r t h e r h e a t i n g t o 1155°C ( p o i n t Q, F i g u r e 17) caused some n e t e x p a n s i o n .  A t a c o n s t a n t temperature o f  1155°C, t h e r a t e o f s o l i d s t a t e s i n t e r i n g was s u f f i c i e n t l y h i g h t o produce a measureable amount o f s h r i n k a g e i n a few minutes.  3.4  S i n t e r i n g Behaviour 3.4.1  o f Fe-22 Cu M i x t u r e s  D i l a t o m e t e r P l o t f o r PCM-2-20 The  c o r r e c t e d d i l a t o m e t e r p l o t f o r an Fe-22% Cu  mixed-powder compact, PCM-2-20, heated w i t h t h e 'normal' c y c l e ,  74  i s presented  i n F i g u r e 18.  The form o f t h e curve i s t y p i c a l  o f t h a t o b t a i n e d f o r a l l Fe-Cu specimens, i n w h i c h t h e f i v e stages of dimensional observed.  change i n d i c a t e d i n F i g u r e 18 were  I n f l e c t i o n s i n t h e c u r v e , a t p o i n t s A, B, C and D  r e p r e s e n t times a t w h i c h one dominant p r o c e s s  of expansion  or c o n t r a c t i o n e i t h e r ended o r gave way t o a new and more r a p i d process.  P o i n t s A, B, C and D a r e s i m p l y maxima o r  minima i n t h e d i l a t o m e t e r c u r v e , f o r w h i c h an e q u i v a l e n t was o b s e r v e d i n p l o t s f o r a l l Fe-Cu compacts. The  f i r s t e i g h t d i l a t o m e t r i c runs l i s t e d i n T a b l e  X I I (PCM-2-12 t o PCM-2-22) were e s s e n t i a l l y r e p r o d u c t i o n s o f p o r t i o n s o f Run PCM-2-20, i n w h i c h t h e h e a t i n g was at various shorter i n t e r v a l s . are i n d i c a t e d i n F i g u r e 19.  The e n d - p o i n t s  terminated  of these  The purpose o f those runs was  to p r o v i d e specimens f o r m e t a l l o g r a p h i c e x a m i n a t i o n to  runs  i n order  study t h e s t r u c t u r a l changes a s s o c i a t e d w i t h t h e v a r i o u s  stages o f dimensional  change o b s e r v e d i n F i g u r e 18.  The  s h o r t runs i n d i c a t e d t h a t t h e e a r l y p o r t i o n s o f Run PCM-2-20 c o u l d be r e p r o d u c e d w i t h an a c c u r a c y  3.4.2  S o l i d State Dimensional  o f ±0.15% A L / L . 0  Changes  Stage I i n F i g u r e 18 i s analogous t o t h e f i r s t p a r t o f t h e d i l a t o m e t e r curve f o r t h e pure i r o n specimen o f comparable powder s i z e  (up t o p o i n t J i n F i g u r e 17) i n w h i c h  simple thermal expansion i n i t i a l l y occurred.  Because copper  75  Table X I I Runs which were R e p r o d u c t i o n s o f t h e E a r l y Stages o f PCM-2-20. A l l Runs were Made w i t h t h e 'Normal' Heating Cycle.  Sample  Run was stopped a t : time  (mins)  temperature  PCM-2-12  9.8  1000°  PCM-2-13  12.6  1040°  PCM-2-6  13.5  1060°  PCM-2-5  14.0  1070°  PCM-2-21  14.1  107 5°  PCM-2-18  •14.. 5  1100°  PCM-2-17  16.0  1155°  PCM-2-22  •17.4  1155°  PCM-2-20  122.2  1155°  (°C)  3.0  F i g u r e 19.  E a r l y s t a g e s o f Run PCM-2-20, showing where samples i n T a b l e X I I were stopped.  78  has a h i g h e r t h e r m a l e x p a n s i o n c o e f f i c i e n t than i r o n i n t h i s temperature r a n g e , and because t h e r e i s a degree o f c o n t i n u i t y o f copper i n p o r t i o n s o f Fe-Cu compacts, a g r e a t e r amount o f e x p a n s i o n i s seen i n t h e l a t t e r .  Toward t h e end  o f Stage I , s o l i d s t a t e s i n t e r i n g s h r i n k a g e o c c u r r e d s i m u l t a n e o u s l y w i t h t h e r m a l e x p a n s i o n , and t h e n e t r a t e o f dimens i o n a l change d e c l i n e d .  A t p o i n t A i n F i g u r e 18 (the end  o f Stage I ) , t h e s i n t e r i n g s h r i n k a g e r a t e exceeded t h e t h e r m a l e x p a n s i o n r a t e and t h e c u r v e assumed a n e g a t i v e slope.  D u r i n g Stage I I (from A t o B i n F i g u r e 1 8 ) , s o l i d  s t a t e s i n t e r i n g was so r a p i d t h a t a marked n e t c o n t r a c t i o n o f t h e specimen was seen, even though t h e temperature was rising.  A t B, where a temperature o f 1065°C t o 1070°C was  a t t a i n e d , t h e r a t e o f c o n t r a c t i o n f u r t h e r i n c r e a s e d , as a r e s u l t o f t h e o n s e t o f m e l t i n g o f copper, w h i c h i s d i s c u s s e d below. Thus t h e b e h a v i o u r o f t h e pure i r o n and t h e Fe^-22% Cu compacts was s t r i k i n g l y d i f f e r e n t above about 800°C w i t h t h e same h e a t i n g c y c l e .  I t i s apparent t h a t s o l i d  state  s i n t e r i n g o f Fe-Cu powder m i x t u r e s was much more r a p i d t h a n t h a t o f pure i r o n powder o f t h e same p a r t i c l e s i z e and a p p r o x i m a t e l y t h e same i n i t i a l d e n s i t y .  While t h i s o b s e r v a t i o n  i s i n t e r e s t i n g , i t has n o t been e x p l o r e d i n d e t a i l i n t h e present i n v e s t i g a t i o n ? x  79  3.4.3  The Onset o f M e l t i n g  The o p t i c a l m i c r o s t r u c t u r e s o f PCM-2-12 ( F i g u r e 20) and PCM-2-13 (not shown), w h i c h were h e a t e d t o 1000°C and 1040°C r e s p e c t i v e l y , were i d e n t i c a l and n o t d i s t i n g u i s h a b l e from t h o s e o f comparable a s - c l e a n e d Fe-Cu-specimens (see S e c t i o n 3.1). M e t a l l o g r a p h i c s e c t i o n s o f t h e compacts PCM-2-6, PCM-2-25 and PCM-2-21 (which ,were heated t o 1060°C, 1070°C and 1075°C) were t a k e n p a r a l l e l t o t h e l o n g i t u d i n a l  axis,  t h r o u g h t h e c e n t r e o f t h e compacts, as shown i n F i g u r e 21. A photomicrograph o f t h e f i n a l s t r u c t u r e o f PCM-2-6 a t l o c a t i o n A (near t h e t o p o f t h e compact, see F i g u r e 21) w h i c h was t y p i c a l o f t h e s t r u c t u r e a t a l l l o c a t i o n s i n t h e sample i s r e p r o d u c e d i n F i g u r e 22. copper a r e c l e a r l y v i s i b l e .  Discrete p a r t i c l e s of  Many had been deformed  (during  compaction) b u t none had m e l t e d as a r e s u l t o f h e a t i n g t o 1060°C ( a t t h e specimen c e n t r e ) .  F i g u r e 22 a l s o r e v e a l s  the t y p i c a l l y i r r e g u l a r shape o f t h e E a s t o n i r o n powder p a r t i c l e s , some o f w h i c h c o n t a i n e d i n t e r n a l p o r e s . F i g u r e 23 i s a p h o t o m i c r o g r a p h o f t h e s t r u c t u r e a t l o c a t i o n B i n sample PCM-2-21, t h e c e n t r e o f w h i c h r e a c h e d 1075°C.  The copper had o b v i o u s l y m e l t e d and f l o w e d t h r o u g h  the compact.  The same s t r u c t u r e was o b s e r v e d a t a l l  locations  i n t h a t sample; i . e . a l l t h e copper had m e l t e d by t h e time the c e n t r e o f t h e compact reached 1075°C.  F i g u r e 20. A s e c t i o n o f sample PCM-2-12 a t lOOx. The specimen was h e a t e d t o 1000°C w i t h a normal h e a t i n g c y c l e . The l i g h t areas a r e copper; t h e dark g r e y a r e a s , i r o n ; and t h e b l a c k a r e a s , v o i d s . ( N i t a l etch)  F i g u r e 21.  S e c t i o n o f compacts used f o r m e t a l l o g r a p h y . A, B, C and D a r e d i f f e r e n t l o c a t i o n s w h i c h were examined by o p t i c a l m i c r o s c o p y .  at i t s centre.  ( N i t a l etch)  F i g u r e 23. A s e c t i o n i n sample PCM-2-21 a t 300x, t a k e n a t l o c a t i o n "B". The specimen was h e a t e d 1075°C a t its c e n t r e . ( N i t a l etch)  82  In to  sample PCM-2-5, the c e n t r e o f w h i c h was  heated  1070°C, the e x t e n t o f m e l t i n g o f the copper v a r i e d w i t h  p o s i t i o n i n the compact. scopically  T h i s c o u l d be d e t e c t e d macro-  (see F i g u r e 24)  25 t o 31).  and m i c r o s c o p i c a l l y (see F i g u r e s  Near the top o f the specimen, a t p o s i t i o n s A  B, no copper had m e l t e d  (see F i g u r e s 25 and  26).  C and D some, o r a l l , o f the copper had m e l t e d f l o w through  the compact (see F i g u r e s 27 and  and  At p o s i t i o n s  and begun t o  28).  Pores  were c r e a t e d where copper f o r m e r l y e x i s t e d as d i s c r e t e p a r t i c l e s , and many o f the o r i g i n a l v o i d s between i r o n p a r t i c l e s were filled. at  More e x t e n s i v e f l o w o f l i q u i d copper was  p o s i t i o n s C and D  ( F i g u r e s 29 and  evident  30), and t h e p o r e s  left  b e h i n d by the moving copper were even l a r g e r than a t p o s i t i o n B  (Figure  31). The v a r i a t i o n s o b s e r v e d i n the  ( F i g u r e 24)  can thus be i n t e r p r e t e d i n terms o f v a r i a t i o n s  i n t h e s i z e and d i s t r i b u t i o n o f p o r e s . in  macrostructure  The v o i d s are l a r g e s t  a c e n t r a l zone of the compact ( i d e n t i f i e d as A r e a #1 i n  F i g u r e 24), i n d i c a t i n g t h a t t h a t zone r e a c h e d t h e m e l t i n g temperature f i r s t .  Copper i n r e g i o n s n e a r the top and  of the compact (Areas #2V,and #3 i n F i g u r e 24) was not melted  o r was  melted  c e n t r a l r e g i o n (Area #1).  either  f o r a s h o r t e r time than i n the Thus a t e m p e r a t u r e g r a d i e n t  e x i s t e d i n the compact when the c e n t r e was  bottom  a t 1070°C.  F i g u r e 24. Macrophoto o f PCM-2-5 a t 5x. The specimen was heated 1070°C a t t h e c e n t r e , t h e s e c t i o n was t a k e n almost through t h e c e n t r e o f t h e compact ( i . e . .035" away). ( N i t a l etch)  F i g u r e 25.  A s e c t i o n i n sample PCM-2-5 a t 300x, t a k e n a t p o s i t i o n 'A'. ( N i t a l etch)  F i g u r e 27.  A s e c t i o n i n sample PCM-2-5 a t 300x, t a k e n a t l o c a t i o n *C'. ( N i t a l etch)  F i g u r e 28. A s e c t i o n i n specimen PCM-2-5 a t 300x, t a k e n a t p o s i t i o n 'D'. ( N i t a l etch)  F i g u r e 29. A s e c t i o n i n specimen PCM-2-5 a t lOOx, t a k e n at l o c a t i o n 'C. ( N i t a l etch)  F i g u r e 31.  A s e c t i o n i n specimen PCM-2-5 at lOOx, taken at p o s i t i o n 'B . 1  87  3.4.4  Temperature  Gradients  i n the Dilatometer  To summarize, t h e o b s e r v a t i o n s a)  There in  was no m e l t i n g  a compact  heated  Specimens  i n S e c t i o n 3.4.3:  of copper  anywhere  t o I060°C a t t h e  centre. b)  There in  was m e l t i n g  a compact  of copper  heated  everywhere  t o I075°C a t t h e  ce nt r e . c)  There  was m e l t i n g  which  reached  of copper  in a  region  I070°C.  I t s h o u l d a l s o be noted t h a t i n d i l a t o m e t r i c r u n s , t h e s t a r t o f r a p i d Stage I I I c o n t r a c t i o n ( P o i n t B ) , which was a s s o c i a t e d w i t h t h e m e l t i n g o f copper, c o n s i s t e n t l y o c c u r r e d when t h e c e n t r e o f t h e compact reached 1065°C t o 1070°C. ture gradients  The tempera-  (both v e r t i c a l and d i a m e t r a l ) , i n compacts  are t h e r e f o r e u n l i k e l y t o have exceeded  5 t o 10°C a t t h e  m e l t i n g temperature o f t h e copper. M e l t i n g o f t h e copper i n t h e compacts was observed t o o c c u r a t temperatures between 1065°C and 1070°C. e q u i l i b r i u m m e l t i n g p o i n t o f pure copper i s 1084.5°C.  The It  i s t h e r e f o r e e v i d e n t t h a t t h e compacts c o n t a i n e d one o r more i m p u r i t i e s w h i c h l o w e r e d t h e m e l t i n g p o i n t o f copper t o below 1070°C.  M e t a l l i c i m p u r i t i e s can account f o r o n l y 2 t o 3  88  degrees o f t h e d e c r e a s e .  The o n l y r e m a i n i n g p o s s i b i l i t y  is  t h a t oxygen was p r e s e n t i n t h e compacts a t m e l t i n g . I n S e c t i o n 3.2, a w e i g h t l o s s o f up t o 0.2 w e i g h t % by t h e compacts, f o l l o w i n g m e l t i n g , was  a t t r i b u t e d t o the  removal o f r e s i d u a l oxygen d u r i n g l i q u i d - p h a s e s i n t e r i n g . According  t o t h e Cu-0 phase-diagram,  0.2 w e i g h t % oxygen i n  copper l o w e r s t h e l i q u i d u s temperature of copper t o 1068°C and, as l i t t l e as 0.002% oxygen l o w e r s t h e s o l i d u s temperat u r e t o 1066°C.  I t i s t h e r e f o r e concluded t h a t the presence  of oxygen i n t h e compacts caused t h e low observed m e l t i n g p o i n t o f t h e copper.  3.4.5  M i c r o s t r u c t u r a l Changes C o i n c i d e n t w i t h M e l t i n g I n Run PCM-2-5 m e l t i n g o f t h e copper was  observed  t o have been complete near t h e c e n t r e o f t h e compact w h i c h r e a c h e d 1070°C.  A t t a c k on the i r o n powder by t h e  liquid  copper was e x t e n s i v e , as r e v e a l e d i n F i g u r e s 27, 28 and Extremely f i n e i r o n p a r t i c l e s  32.  (some l e s s t h a n one m i c r o n i n  d i a m e t e r ) , "'.are observed i n t h e m i c r o s t r u c t u r e a t t h e i n s i d e o f pores and i n the dense i n t e r v o i d areas (see F i g u r e 28). These p a r t i c l e s were a p p a r e n t l y  formed by the d i s i n t e g r a t i o n  of l a r g e r p a r t i c l e s t h r o u g h t h e a c t i o n o f l i q u i d Because  copper.  copper i s c a p a b l e o f d i s s o l v i n g up t o 3.7%  i r o n at  the m e l t i n g temperature, i t i s l i k e l y t h a t a d i s s o l u t i o n p r o c e s s was  i n v o l v e d i n the d i s i n t e g r a t i o n .  F i g u r e 32.  A s e c t i o n i n specimen PCM-2-5 a t 1200x. ( N i t a l etch)  90  Some d i f f u s i o n o f copper a l o n g t h e g r a i n b o u n d a r i e s i s e v i d e n t i n F i g u r e s 2 8 and 32 as dark e t c h i n g bands w i t i n the  iron particles.  Gamma i r o n i s c a p a b l e o f d i s s o l v i n g  7.9% copper a t 1070°C. I n t h e lower l e f t c o r n e r o f F i g u r e 32 i s what may have been a g r a i n boundary  (or p o s s i b l y , a s o l i d neck between  two i r o n p a r t i c l e s ) w h i c h was p e n e t r a t e d o r d i s s o l v e d by l i q u i d copper.  However, t h e m a j o r i t y o f g r a i n b o u n d a r i e s  d i d n o t c o n t a i n l i q u i d copper, and few i n s t a n c e s o f copper h a v i n g p e n e t r a t e d i r o n g r a i n b o u n d a r i e s were o b s e r v e d i n that  sample. A few s o l i d c o n t a c t s between i r o n p a r t i c l e s were  o b s e r v e d i n PCM-2-5 b u t most p a r t i c l e s were found t o be i s o l a t e d from t h e i r n e i g h b o u r s by t h i n f i l m s o f copper w h i c h formed between p a r t i c l e s as a r e s u l t o f t h e p e n e t r a t i o n d i s s o l u t i o n o f necks. diately following  and/or  The s t r u c t u r e o f t h e compacts imme-  m e l t i n g was, t h e n , a d i s p e r s i o n o f i r o n -  r i c h p a r t i c l e s i n a copper m a t r i x , r a t h e r t h a n t h e c o n t i n u o u s i r o n s k e l e t o n which i s e x p e c t e d i n a s o l i d - s t a t e  sintered  aggregate.  3.4.6  S t r u c t u r a l Changes i n Stages I I I , IV and V F i g u r e 33 i s a h i g h m a g n i f i c a t i o n  photomicrograph  of PCM-2-18 w h i c h was stopped a t t h e end o f Stage I I I ( a t 1100°C).  P o o l s o f copper a r e observed i n t h e g r a i n b o u n d a r i e s  91  F i g u r e 33.  A s e c t i o n i n sample PCM-2-18, 1200x.  ( N i t a l etch)  92  of the l a r g e r i r o n p a r t i c l e s  ( i n Figure 33), i n d i c a t i n g t h a t  the p e n e t r a t i o n o f i r o n g r a i n b o u n d a r i e s by l i q u i d  copper  was underway i n Stage I I I . D i f f u s i o n o f copper a l o n g the i r o n g r a i n b o u n d a r i e s (shown by the d a r k e r areas a d j a c e n t t o the b o u n d a r i e s ) and volume d i f f u s i o n o f copper i n t o t h e i r o n , are b o t h e v i d e n t .  \v-...ra 34 ohows  c  • J  ~r  F i g u r e 34 shows a n o t h e r a r e a i n t h e same sample. The t h i n f i l m s o f copper s e p a r a t i n g a d j a c e n t i r o n p a r t i c l e s were t y p i c a l o f t h e sample and i n d i c a t e t h a t the d i h e d r a l a n g l e of t h e system was  zero.  The s t r u c t u r e a t t h e end o f  Stage I I I can s t i l l be d e s c r i b e d as  'dispersed'.  F i g u r e s 35 t o 38 a r e photomicrographs of PCM-2-17 w h i c h was  stopped a p p r o x i m a t e l y h a l f - w a y through Stage IV  expansion.  The p o l i s h i n g and e t c h i n g t e c h n i q u e f o r t h e  samples i n F i g u r e 35 t o 38 were i d e n t i c a l t o t h o s e used i n p r e p a r i n g p r e v i o u s samples.  The d i f f e r e n c e s between t h e  Stage I I I and Stage IV s t r u c t u r e s a r e c o n s i d e r a b l e . P e n e t r a t i o n o f a few i r o n g r a i n b o u n d a r i e s by copper was  i n p r o g r e s s i n t h e l a r g e p a r t i c l e i n the c e n t r e o f  F i g u r e 35.  Both g r a i n boundary  and volume d i f f u s i o n o f  copper i n t o the i r o n were underway and were more  advanced  than i n the Stage I I I s t r u c t u r e s . F i g u r e s 36 and 37 show t h a t t h e s t r u c t u r e was 'dispersed'.  still  S m a l l p a r t i c l e s o f i r o n were fewer and o f  l a r g e r average d i a m e t e r t h a n they were i n samples w h i c h were stopped i n Stage I I I . The d i s a p p e a r a n c e o f t h e s m a l l e s t  F i g u r e 37.  A s e c t i o n i n PCM-2-17, 300x.  ( N i t a l etch)  95  F i g u r e 38.  A s e c t i o n i n PCM-2-22, 1200x.  ( N i t a l etch)  96  p a r t i c l e s i n d i c a t e s the operation of a s o l u t i o n - r e p r e c i p i t a t i o n p a r t i c l e growth p r o c e s s d u r i n g Stages I I I and I V . Not o n l y s m a l l p a r t i c l e s , b u t a l s o areas o f s m a l l r a d i u s o f c u r v a t u r e i n l a r g e r p a r t i c l e s d i s s o l v e d p r e f e r e n t i a l l y and r e p r e c i p i t a t e d on s u r f a c e s o f l a r g e r r a d i u s . F i g u r e s 38 and 39 show s e c t i o n s o f PCM-2-22 w h i c h had a l m o s t completed Stage IV e x p a n s i o n when t h e r u n was stopped.  The average p a r t i c l e s i z e a f t e r s i n t e r i n g was l a r g e r  t h a n i n samples stopped a t e a r l i e r t i m e s , due t o t h e s o l u t i o n r e p r e c i p i t a t i o n mechanism (compare F i g u r e s 39 and 3 7 ) . The e l i m i n a t i o n o f s m a l l ia?on p a r t i c l e s was v i r t u a l l y complete by t h e end o f Stage I V . Many p a r t i c l e s e x h i b i t e d n o n - s p h e r i c a l shapes r e s u l t i n g from t h e d i s i n t e g r a t i o n o f the o r i g i n a l  (more s p h e r i c a l ) i r o n p a r t i c l e s by g r a i n boundary  penetration.  The l o n g t h i n f i l m s o f copper s e p a r a t i n g  solid  s u r f a c e s i n t h e l o w e r r i g h t a r e a o f t h e photograph i n F i g u r e 3 8 a r e t y p i c a l o f t h e specimen, and a r e b e l i e v e d t o have r e s u l t e d from t h e complete p e n e t r a t i o n o f an a u s t e n i t e g r a i n boundary  (or b o u n d a r i e s ) .  The p r e s e n c e o f copper i n  such a narrow c a p i l l a r y i n d i c a t e s t h a t t h e d i h e d r a l a n g l e o f t h e system was zero l a t e i n Stage IV. As e x p e c t e d , t h e d i f f u s i o n o f copper i n t o t h e i r o n was even more advanced i n PCM-2-22 than i n s h o r t e r - r u n samples. However, t h e p r o p o r t i o n o f l i g h t e t c h i n g r e g i o n s , w h i c h were not a l l o y e d t o more than 1% copper was s t i l l l a r g e , i n d i c a t i n g  97  98  t h a t d i f f u s i o n was by no means complete. g r a i n boundaries  V i r t u a l l y a l l the  i n t h e i r o n had been p e n e t r a t e d by copper  i n PCM-2-22. F i g u r e s 40 and 41 a r e photomicrographs o f PCM-2-20, w h i c h was h e l d f o r 100 minutes a t 1155°C.  The degree o f  i r o n p a r t i c l e - i r o n p a r t i c l e c o n t i g u i t y ( c o n t a c t ) was so e x t e n s i v e t h a t t h e r e can be no doubt t h a t t h e d i h e d r a l angle had become g r e a t e r t h a n zero a t t h i s stage i n s i n t e r i n g .  In  f a c t , t h e i r o n - r i c h p a r t i c l e s i n PCM-2-20 e x i s t e d as a s o l i d s k e l e t o n w i t h copper f i l l i n g many o f t h e v o i d s i n t h e skeleton. The  i r o n ' p a r t i c l e s ' i n PCM-2-20 were more s p h e r i c a l ,  and had even more r e g u l a r s u r f a c e s t h a n those i n PCM-2-22. They were a l s o shaped i n such a manner as t o a l l o w h i g h p a c k i n g e f f i c i e n c y , as i f t h e K i n g e r y p r e s s u r e ' mechanism had o p e r a t e d positive.  ' s o l u t i o n due t o  i n Stage V b e f o r e <j> became  There i s f u r t h e r e v i d e n c e  of coalescence  of i r o n  p a r t i c l e s i n F i g u r e 40 where l a r g e necks had formed between adjacent i r o n p a r t i c l e s . The  f o l l o w i n g o b s e r v a t i o n s were made c o n c e r n i n g  the e v o l u t i o n o f t h e pore s t r u c t u r e d u r i n g Stages I I I , IV and V: A)  In S t a g e were  I I ( s e e F I g u re- 4-2) :  small  through  and e v e n l y  t h e compact.  voids  distributed  F i g u r e 40.  A s e c t i o n i n PCM-2-20, 300x.  ( N i t a l etch)  100  F i g u r e 42.  A s e c t i o n i n PCM-2-6, lOOx.  ( N i t a l etch)  101  B)  In  late  the  Stage  copper  through voids  had m e l t e d  t h e compact  where  existed.  separated  denser  In the  Stage  pore  leaving  voids iron  ( F i g u r e s . 44 was  that  The  were  more e v e n l y  In  late  pores then  Stage  were  Stage I I I . distributed  Few  large  remained.  (see Figure numerous  Stage  again existed  coalescence was  V  less  in late  areas  in late  the compact. areas  and 4 5 ) :  strikingly  from  intervoid  and  areas).  different pores  large  copper  areas of  structure  throughout  D)  IV  dispersed  Those  (intervoid  late  and  the o r i g i n a l  particles  copper  C)  I I I ( s e e F i g u r e . .43):  between  IV. and iron  46):  and Large  the  smaIler intervoid  extensive particles  evident.  The change i n pore d i s t r i b u t i o n i n Stage I V , t o a more r e g u l a r d i s t r i b u t i o n , i s c o n s i d e r e d t o have r e s u l t e d the d i s s o l u t i o n denser i n t e r v o i d clusters  of c l u s t e r s  from  of small i r o n p a r t i c l e s i n the  areas d u r i n g Stages I I I and IV.  When t h o s e  d i s s o l v e d , c a p i l l a r i e s between s m a l l p a r t i c l e s  F i g u r e 43.  F i g u r e 44.  A s e c t i o n i n PCM-2-18, lOOx. ( N i t a l etch)  A s e c t i o n i n PCM-2-22 (Area #1), lOOx. ( N i t a l etch)  F i g u r e 46.  A s e c t i o n i n PCM-2-20, lOOx.  ( N i t a l etch)  104 (which tended t o h o l d l i q u i d i n them) were removed. l i q u i d r e t r e a t e d from those a r e a s l e a v i n g v o i d s .  The  Large i r o n  p a r t i c l e s f a i l e d t o c o l l a p s e i n t o t h e v o i d s and f i l l  them,  because t h e p a r t i c l e s s u r r o u n d i n g t h e v o i d s had b r i d g e d . The uneven d i s t r i b u t i o n o f v o i d s a t t h e end o f Stage V l i k e l y r e s u l t e d from t h e c l o s i n g o f t h o s e same v o i d s (which were p r o b a b l y s m a l l e r t h a n t h o s e which formed when copper melted) as a r e s u l t o f Stage V s h r i n k a g e . F i g u r e 47 shows t h e e x t e r n a l s u r f a c e o f PCM-2-18 (which was s t o p p e d i n Stage I I I ) .  The photograph r e v e a l s  i r o n p a r t i c l e s w i t h copper between them.  The i r o n p a r t i c l e  f a c e s were f l a t t e n e d i n t h e compaction p r o c e s s .  The s u r f a c e  o f t h e copper made a s m a l l a n g l e w i t h t h e s u r f a c e o f t h e i r o n p a r t i c l e s , i n d i c a t i n g t h a t w e t t i n g was complete o r almost complete ( i . e . 6 = 0°) i n Stage I I I . F i g u r e 48 shows the s u r f a c e o f PCM-2-20 ( a f t e r 100 minutes a t 1155°C) and i n d i c a t e s t h a t t h e w e t t i n g o f t h e i r o n by t h e copper was i n c o m p l e t e i n l a t e Stage V.  The  copper had 'beaded' t o meet t h e i r o n s u r f a c e s a t r e l a t i v e l y large angles. F i g u r e 49 i s an absorbed e l e c t r o n image o f PCM-2-20. The photograph i n d i c a t e s t h a t t h e i r o n p a r t i c l e s were i n s o l i d c o n t a c t w i t h each o t h e r around t h e l a r g e p o r e s ( i . e . b r i d g e d ) , thus c a u s i n g t h o s e v o i d s t o remain i n t h e s t r u c t u r e . F i g u r e 50 i s a copper X^r.ay image o f t h e same a r e a w h i c h  F i g u r e 47.  F i g u r e 48.  S u r f a c e o f PCM-2-18 a t 2000x; viewed through a scanning e l e c t r o n microscope. The o x i d e ' f l o w e r s ' formed d u r i n g s t o r a g e a f t e r l i q u i d - p h a s e s i n t e r i n g .  S u r f a c e o f PCM-2-20 a t 1040x, as viewed w i t h a scanning e l e c t r o n microscope.  F i q u r e 49. Absorbed e l e c t r o n image o f a s e c t i o n i n PCM-2-20; 100Ox. The l i g h t grey areas a r e i r o n , t h e dark g r e y a r e a s a r e copper. The w h i t e a r e a i s a v o i d .  F i q u r e 50.  Copper X-ray image o f a s e c t i o n i n PCM-2-20; lOOOx. The l i g h t areas a r e h i g h m copper c o n c e n t r a t i o n . The b l a c k a r e a ( l e f t s i d e ) i s a v o i d . T h i s s e c t i o n i s t h e same as t h a t shown i n F i g u r e 49.  107  i n d i c a t e s t h a t t h e copper d i d n o t form a c o n t i n u o u s  film  on t h e i n s i d e o f t h e p o r e s .  incomplete  The w e t t i n g was, t h e n ,  as t h e s u r f a c e morphology i n F i g u r e 48 i n d i c a t e d .  F i g u r e 50  a l s o i n d i c a t e s t h a t a l l o y i n g o f t h e i r o n w i t h t h e copper was not complete a t t h e c e n t r e s o f l a r g e i r o n p a r t i c l e s 100 m i n u t e s a t 1155°C.  after  A n a l y s e s made w i t h t h e e l e c t r o n  microprobe analyzer i n d i c a t e d t h a t the centre of l a r g e i r o n p a r t i c l e s i n PCM-2-20 c o n t a i n e d a p p r o x i m a t e l y  4% copper.  A s i m l L l a r m i n v e s t i g a t i o n o f pores i n PCM-2-22 and PCM-2-18 d i d n o t r e v e a l whether o r n o t w e t t i n g was complete because d i f f u s i o n zones ( a t t h e s u r f a c e o f i r o n p a r t i c l e s a b u t t i n g v o i d s ) made i t i m p o s s i b l e t o d e t e r m i n e whether l i q u i d copper coated t h e i r o n s u r f a c e s o r i f t h e o b s e r v e d copper c o n c e n t r a t i o n was due t o d i f f u s i o n . I t i s concluded  t h a t t h e w e t t i n g was v i r t u a l l y  complete d u r i n g Stages I I I and I V , w h i l e a t t h e end o f Stage V i t was  incomplete.  3.4.7  Summary o f M e t a l l o g r a p h i c  Observations  A summary o f t h e o b s e r v a t i o n s made i n t h e p r e v i o u s section follows:  108  M a c r o s c o p i c Occurrences  Metallographic  Observations  Copper d i s p e r s e s through t h e compact w e t t i n g i r o n p a r t i c l e s .  Copper m e l t s , Stage I I I begins  V o i d s remain where copper had e x i s t e d as powder p a r t i c l e s . Small i r o n p a r t i c l e s are b r o k e n l o o s e by l i q u i d copper. G r a i n boundary d i f f u s i o n begins. I r o n s k e l e t o n i s b r o k e n up by s o l u t i o n o f i r o n i n copper. Necks a r e p e n e t r a t e d s o l v e d by copper.  or d i s -  Dense i n t e r v o i d areas formed. G r a i n boundary p e n e t r a t i o n becomes a p p a r e n t .  Stage I I I c o n t r a c t i o n i s overcome by Stage IV expansion  D i f f u s i o n ( g r a i n boundary and volume) i s more advanced. 10  Diffusion at solid i s observed.  contacts  11  P e n e t r a t i o n of g r a i n boundaries becomes e x t e n s i v e .  12  More s o l i d - s o l i d c o n t a c t s a r e o b s e r v e d t h a n d u r i n g Stage I I I .  13  Small i r o n p a r t i c l e s d i s appearing .  14  I r r e g u l a r p a r t i c l e shapes observed.  15  I r o n p a r t i c l e s have more regular surfaces.  109  Macroscopic Occurrences  Stage V c o n t r a c t i o n begins and a f t e r 100 minutes:  3.5  Metallographic  16)  Pores are more evenly d i s t r i buted than during Stage I I I ; no high d e n s i t y r e g i o n s remain.  IT).  Iron p a r t i c l e s are not a s o l i d skeleton.  18'))  Small i r o n p a r t i c l e s are gone.  1-93))  Iron p a r t i c l e s have equiaxed shapes and r e g u l a r s u r f a c e s .  210'))  Iron p a r t i c l e s are shaped f o r dense packing.  2?1T  Iron p a r t i c l e s are i n the form of a s o l i d s k e l e t o n .  22*)  There i s o n l y p a r t i a l w e t t i n g of i r o n by the copper.  23)  Pore d i s t r i b u t i o n i s uneven.  22m  D i f f u s i o n i s not complete i n group PCM-2-XX.  Proposed Mechanisms of S i n t e r i n g Metallographic  Observations  i n Fe-22 Cu  Mixtures  and d i l a t o m e t r i c o b s e r v a t i o n s  PCM-2-20 (see F i g u r e 51) permit  an a n a l y s i s of the mechanisms  operating during liquid-phase s i n t e r i n g  i n the p r e s e n t  Immediately f o l l o w i n g m e l t i n g of copper, the i r o n s t r u c t u r e formed by p r i o r s o l i d - s t a t e destroyed  by d i s s o l u t i o n  the d i h e d r a l angle  i s zero.  study. skeletal  sintering i s  of i r o n i n the copper and  between s o l i d p a r t i c l e s are p e n e t r a t e d . complete and  for  necks  I n i t i a l l y wetting i s Coincident  with,  3.0  F i g u r e 51.  Dilatometer p l o t f o r 63u powders).  Run PCM-2-20.  (Normal h e a t i n g , 22% copper, 53 t o  i—• o  Ill  and f o l l o w i n g  disintegration  shrinkage occurs.  o f t h e i r o n s k e l e t o n , Stage I I I  Stage I I I i s a p e r i o d i n w h i c h t h e compact  undergoes e x t e n s i v e s h r i n k a g e (1.32 % ( A L / L ) i n PCM-2-20) 0  a t a r a t e which i s h i g h and v i r t u a l l y c o n s t a n t .  Only  one  d e n s i f i c a t i o n p r o c e s s seems t o be c a p a b l e o f p r o d u c i n g such r a p i d , e x t e n s i v e and l i n e a r c o n t r a c t i o n ; i . e . rearrangement. The rearrangement p r o c e s s w h i c h K i n g e r y [3] proposed as t h e f i r s t d e n s i f i c a t i o n mechanism t o o p e r a t e i n l i q u i d phase s i n t e r i n g i n v o l v e s repacking of the s o l i d p a r t i c l e s w i t h the a i d of v i s c o u s f l o w , which has a l i n e a r r a t e .  A l l other  s u g g e s t e d d e n s i f i c a t i o n p r o c e s s e s have a r a t e w h i c h i s expected t o decrease w i t h time. Stage I I I i s thus c o n s i d e r e d t o be t h e r e s u l t o f rearrangement o f s o l i d p a r t i c l e s t o a h i g h e r p a c k i n g e f f i c i e n c y than t h a t w h i c h e x i s t e d a t m e l t i n g . the d i s s o l u t i o n o f i r o n by copper.  The p r o c e s s i s a i d e d by That b r e a k s i r r e g u l a r  i r o n p a r t i c l e s i n t o s m a l l e r , more e q u i a x e d f r a g e m e n t s , and  also  reduces t h e volume o f t h e s o l i d i r o n by 0.80%(AV/Vo), o r 0.26%(AL/Ln).  However, u n l e s s t h e d i h e d r a l a n g l e i s z e r o  i n t h e system a t t h i s s t a g e , s o l i d - s o l i d c o n t a c t s would r a p i d l y r e f o r m , and s o l i d p a r t i c l e s c o u l d n o t s l i d e p a s t each o t h e r t o r e p a c k .  The complete w e t t i n g i n Stage I I I  a l s o gives r i s e to the c a p i l l a r y p r e s s u r e which d r i v e s rearrangement. The sharp t r a n s i t i o n from Stage I I I c o n t r a c t i o n t o Stage IV e x p a n s i o n i n PCM-2-20 (see F i g u r e 51) s u g g e s t s t h a t  112  s h r i n k a g e may n o t be complete when Stage IV e x p a n s i o n s t a r t s , but t h a t i t c o n t i n u e s i n t o Stage IV and i s 'masked' by t h e r a p i d expansion processes.  Even when s h r i n k a g e due t o r e -  arrangement i s complete, o t h e r i m p o r t a n t c o n t r a c t i o n p r o c e s s e s would be e x p e c t e d t o c o n t i n u e as l o n g as t h e d i h e d r a l a n g l e was z e r o and t h e r e was c o n t i n u e d e x i s t e n c e o f a c a p i l l a r y pressure.  F o r example, K i n g e r y ' s ' s o l u t i o n due t o p r e s s u r e '  mechanism would be e x p e c t e d t o o p e r a t e beyond t h e end o f rearrangement, a l t h o u g h t h e t h e o r y p r e d i c t s t h a t t h e r a t e o f s h r i n k a g e would be l o w e r .  However, i n Stage IV any i n t r i n s i c  s h r i n k a g e from ' s o l u t i o n due t o p r e s s u r e ' i s a p p a r e n t l y masked by i n t e r v e n i n g e x p a n s i o n p r o c e s s e s . The n e t e x p a n s i o n i n Stage I V i s b o t h e x t e n s i v e and extremely r a p i d . i s 1.50  %(AL/L ) 0  The observed r a t e o f e x p a n s i o n i n PCM-2-20 p e r minute e a r l y i n Stage IV.  I n view o f  the  f a c t t h a t some i n t r i n s i c s h r i n k a g e i s masked by e x p a n s i o n ,  the  r a t e o f t h e e x p a n s i o n p r o c e s s e s i n Stage IV must be v e r y  high. D i f f u s i o n and g r a i n boundary p e n e t r a t i o n i n t h e i r o n w i l l produce n e t e x p a n s i o n o n l y i f t h e s o l i d p a r t i c l e s a r e c l o s e l y packed; i . e . o n l y a f t e r rearrangement i s e s s e n t i a l l y complete.  Any d i f f u s i o n o f copper i n t o i r o n w h i c h o c c u r s ,  b e f o r e rearrangement i s complete, w i l l lower t h e observed r a t e o f c o n t r a c t i o n by i n c r e a s i n g t h e volume o f t h e s o l i d . G r a i n boundary p e n e t r a t i o n w h i c h o c c u r s b e f o r e  rearrangement  i s complete may, o r may n o t , cause a d e c r e a s e i n t h e n e t r a t e  113  of shrinkage.  That depends on the d e n s i t y o f p a c k i n g i n t h e  r e g i o n s u r r o u n d i n g a p a r t i c l e i n which a g r a i n boundary i s penetrated.  F u r t h e r m o r e , n e t e x p a n s i o n i s observed o n l y i f  the r a t e o f e x p a n s i o n i s g r e a t e r t h a n the r a t e o f s i m u l t a n e o u s shrinkage. The n e t l i n e a r e x p a n s i o n i n Stage IV i n PCM-2-20 was 3.29%-(AL/Lo).  To c o n v e r t t h a t f i g u r e t o volume e x p a n s i o n ,  an e s t i m a t e must be made o f t h e d i a m e t r a l d i m e n s i o n a l change d u r i n g Stage IV. was  0.52%  R e f e r e n c e t o T a b l e XI r e v e a l s t h a t t h e r e  more s h r i n k a g e i n d i a m e t e r t h a n i n l e n g t h d u r i n g t h e  f u l l c o u r s e o f t h e r u n PCM-2-20.  I f i t i s assumed t h a t t h e  same d i f f e r e n c e p r e v a i l e d i n Stage I V , t h e n t h e n e t d i a m e t r a l e x p a n s i o n i n Stage IV was  3.29-0.52 = 2.77%  (AD/D ). 0  This  l e a d s t o a c o n s e r v a t i v e e s t i m a t e o f 9.09%^(AV/Vo) n e t e x p a n s i o n i n PCM-2-20 d u r i n g Stage IV. The maximum e x p a n s i o n which can r e s u l t from s a t u r a t i o n o f the i r o n I n f a c t a l l o y i n g was  complete  ( w i t h 9 wt % copper) i s 9%' (AV/Vo).  found t o be i n an e a r l y s t a t e o f p r o g r e s s  a t the end o f Stage IV ( i n sample PCM-2-22).  Even PCM-2-20  was n o t i n a l l o y e q u i l i b r i u m a f t e r 100 minutes a t 1155°C. can be e s t i m a t e d t h a t not more t h a n 2% volume e x p a n s i o n  was  the d i r e c t r e s u l t o f the d i f f u s i o n o f copper i n t o i r o n i n Stage IV.  I t f o l l o w s t h a t a t l e a s t 7% volume e x p a n s i o n  caused by one o r more o t h e r p r o c e s s e s .  was  I n f a c t , as noted  above, s i m u l t a n e o u s c o n t r a c t i o n was o c c u r r i n g i n Stage IV.  It  114  Thus the amount o f i n t r i n s i c e x p a n s i o n  associated w i t h pro-  c e s s e s o t h e r than a l l o y i n g o f the i r o n was than 7 volume per  substantially greater  cent.  Metallography  d i d not i n d i c a t e the o p e r a t i o n o f  any  p r o c e s s o t h e r than g r a i n boundary p e n e t r a t i o n w h i c h c o u l d cause such e x p a n s i o n ,  and no o t h e r can be suggested w h i c h i s  c o n s i s t e n t w i t h the o b s e r v a t i o n s .  Thus the e v i d e n c e  clearly  p o i n t s t o g r a i n boundary p e n e t r a t i o n as the cause o f most o f the Stage I V , e x p a n s i o n . v i r t u a l l y a l l the Y ~ i ° r  by l a t e Stage IV  The m e t a l l o g r a p h i c o b s e r v a t i o n t h a t n  g r a i n boundaries  had been p e n e t r a t e d ,  ( i n PCM-2-22), i s f u r t h e r evidence  p e n e t r a t i o n caused e x p a n s i o n .  The  that  end o f Stage IV was  appar-  e n t l y c o i n c i d e n t w i t h the c o m p l e t i o n o f t h e p e n e t r a t i o n o f a l l the a v a i l a b l e g r a i n b o u n d a r i e s  i n the group PCM-2-XX.  A g r a i n boundary i s l i k e l y f i r s t p e n e t r a t e d by a mechanism o f d i f f u s i o n i n t o the boundary, p r o g r e s s i n g u n t i l a f i l m o f copper e x i s t s .  That f i l m then expands by t h e movement  o f more copper i n t o the boundary  ( d r i v e n by c a p i l l a r y p r e s s u r e ) .  A p e n e t r a t e d boundary i s i n f a c t a s m a l l c a p i l l a r y and such i s a f a v o u r a b l e l o c a t i o n f o r l i q u i d t o g a t h e r a t .  as In  t h i s manner t h e p e n e t r a t e d boundary grows i n w i d t h t o some equilibrium thickness.  However, l i q u i d i s a l s o h e l d i n o t h e r  areas o f the compact by c a p i l l a r y f o r c e s and t h e  disposition  o f l i q u i d i s c o n t r o l l e d by some s o r t o f h y d r a u l i c e q u i l i b r i u m .  115  The  s e l e c t i v e d i s s o l u t i o n of small p a r t i c l e s i n the  i n t e r v o i d a r e a s , and from t h e i n s i d e o f p o r e s d u r i n g Stage I V , removes some o f t h e s m a l l e s t l i q u i d - h o l d i n g c a p i l l a r i e s . That a l l o w s l i q u i d t o move t o t h o s e g r a i n b o u n d a r i e s w h i c h are p e n e t r a t e d ,  or i n the a c t o f being penetrated.  As a r e s u l t  v o i d s form, where c l u s t e r s o f s m a l l p a r t i c l e s p r e v i o u s l y e x i s t e d , and  l i q u i d i s freed t o ssupply' The  t h e g r a i n boundary c a p i l l a r i e s .  only reported values f o r d i h e d r a l angle i n the  s o l i d i r o n - l i q u i d copper system l i e i n t h e range o f 27 t o 35 degrees (see T a b l e I ) .  I f t h e s e v a l u e s p r e v a i l e d under t h e  c o n d i t i o n s o f l i q u i d phase s i n t e r i n g i n Stage IV and e a r l i e r , n e i t h e r g r a i n boundary p e n e t r a t i o n n o r t h e o b s e r v e d m i c r o s t r u c t u r e c o u l d be e x p l a i n e d .  'dispersed'  I n f a c t , i n the present  work, and i n s t u d i e s d e s c r i b e d by a number o f p r e v i o u s  inves-  t i g a t o r s „[12,14,23], i t i s apparent t h a t a zero d i h e d r a l a n g l e p r e v a i l e d , a t l e a s t w h i l e t h e compacts were u n d e r g o i n g r a p i d expansion. However, a f t e r p r o l o n g e d l i q u i d - p h a s e s i n t e r i n g ( w e l l i n t o Stage V) i n t h e p r e s e n t work, a c o n t i n u o u s i r o n - r i c h s k e l e t o n i s o b s e r v e d , and a p o s i t i v e d i h e d r a l a n g l e was i n d i c a t e d . I t may t h e r e f o r e be c o n c l u d e d t h a t : a)  t h e d i h e d r a l angle changes during t h e course of s i n t e r i n g under t h e c o n d i t i o n s of t h e present ( a n d many p r e v i o u s l y reported) experiments,  b)  reported values of the dihedral angle in t h e Fe-Cu s y s t e m a r e based on measurements on s p e c i m e n s w h i c h h a d b e e n ' s i n t e r e d ' i n t o t h e e q u i v a l e n t o f S t a g e V.  116  Any  change i n d i h e d r a l angle must be a s s o c i a t e d w i t h  a change i n Y  or Y  S L  indicate that Y  '  S S  > Y  i  2  S S  S  S p e c i f i c a l l y , the present  L  the e a r l y stages o f l i q u i d - p h a s e  n  s i n t e r i n g , and t h a t e i t h e r Y O T i n c r e a s e s o r v„„ oLi  such as t o make Y  s s  results  decreases,  00  become e q u a l t o 2 y  S L  i n Stage V.  There  are s e v e r a l p o s s i b l e e x p l a n a t i o n s f o r t h e s e changes: a) becomes the  Yg[_ i n c r e a s e s ,  alloyed  observation  boundaries. decrease  b) of  iron  copper fore  by  contrary  as  copper  should  y 5 j_  occur  increases copper.  i s not c o n s i s t e n t  r a p i d l y along  a rapid  Microprobe with  Yg|_ i n c r e a s e s ,  iron  increase  as S t a g e  analysis  in early  in Y  or  s l  III.  o f Van V l a c k  o r Y55  showed  impurity  III.  (see Section  decreases  the course i s added  There-  1.3.2).  as a r e s u l t o f species,  e l i m i n a t i o n o f some  during  that the  It i s also  interface-active impurity  species,  with  grain  Stage  unsatisfactory.  a r e s u l t of the progressive  an  as t h e i r o n  as a r e s u l t o f t h e d i s s o l u t i o n  to the observations  i s unlikely that  This  as e a r l y  is also  i n t r o d u c t i o n o f an  decreases-,  diffuses  to that,  saturated  interface-active it  that  explanation  c) the  the copper.  liquid  becomes  this  with  According  i n Y55  o r Y55  or  other  of Stage  V.  t o t h e system  Since during  s i n t e r i n g , t h e former case i s u n l i k e l y .  However i f oxygen i s c o n s i d e r e d as t h e i n t e r f a c e - a c t i v e impurity, explanation  (c) becomes a s t r o n g p o s s i b i l i t y .  It is  117  p o s s i b l e t h a t n o t a l l the o x i d e s i n the compacts were c o m p l e t e l y reduced i n the c o u r s e o f c l e a n i n g a t 600°C and 700°C. n o t e d i n S e c t i o n 3.2.2 removed by hydrogen  up t o 0.2 p e r c e n t oxygen may  was  have been  i n t h e d i l a t o m e t e r d u r i n g Stages I I I t o V  ( i n a normal h e a t i n g c y c l e ) . 3.4.4  As  I t was  a l s o noted i n S e c t i o n  t h a t s u f f i c i e n t oxygen was p r e s e n t a t t h e t i m e o f m e l t i n g  of t h e copper t o lower t o l i q u i d u s temperature t o below 1070°C. There i s , t h e r e f o r e , e v i d e n c e t h a t oxygen was p r e s e n t i n t h e specimens  d u r i n g Stages I I I , IV and V i n c o n c e n t r a t i o n s  which  s t e a d i l y decreased w i t h time. I t has been shown by O ' B r i e n and C h a k l a d e r [30] t h a t s m a l l oxygen c o n c e n t r a t i o n s  i n l i q u i d copper a r e s u f f i c i e n t  t o markedly reduce t h e v a l u e o f Y interface.  Moreover  s l  at a  liquid-copper/sapphire  i t i s known t h a t t h e p r e s e n c e o f an  e l e c t r o n e g a t i v e i m p u r i t y i n a l i q u i d m e t a l tends t o reduce the v a l u e s of both y  T T 7  and y  •LiV  C T  [31] .  I t i s t h u s argued,  o Ju  r e l e v a n t t o t h e experiments r e p o r t e d i n t h i s t h e s i s , t h a t enough oxygen i s p r e s e n t i n t h e Fe-Cu specimens I I I and IV t o produce a z e r o d i h e d r a l a n g l e . system l e s s than a 19% r e d u c t i o n o f Y  during  I n t h e Fe-Cu Y )  (for constant  s l  Stages  would be n e c e s s a r y t o s a t i s f y t h e r e q u i r e m e n t t h a t  S S  2Y T 0  -  Ojj  based on (J) = '35°.  (Stage V ) , oxygen i n t h e copper becomes  reduced t o such a l e v e l t h a t 2 Y  s l  is  >  Y  s s  (i.e. a positive  d i h e d r a l a n g l e e x i s t s ) and c o a l e s c e n c e o f s o l i d g r a i n s ensues.  C  OO  I t i s f u r t h e r argued t h a t a t a l a t e r p e r i o d  i n liquid-phase sintering  particles  Yn  (or  118  A p o s s i b l e refinement i n t h i s explanation i n v o l v e s the lowering of Y  s l  due t o d e p o s i t i o n o f oxygen a t t h e l i q u i d  s o l i d i n t e r f a c e s as copper d i f f u s e s i n t o i r o n . copper a c r o s s t h e i n t e r f a c e would decrease  The f l u x o f  as t h e i r o n became  s a t u r a t e d w i t h copper, and oxygen would become d i s p e r s e d more u n i f o r m l y through t h e l i q u i d , a l l o w i n g Y  t o p t  increase.  As t h e p e n e t r a t i o n o f g r a i n b o u n d a r i e s t i o n , Stage IV e x p a n s i o n to  nears  comple-  slows and c o n t r a c t i o n p r o c e s s e s  dominate as Stage V i s e n t e r e d .  begin  The dominant c o n t r a c t i o n  p r o c e s s e a r l y i n Stage V i s c o n s i d e r e d t o be one o f p a r t i c l e shape change by ' s o l u t i o n due t o p r e s s u r e . '  T h i s mechanism,  w h i c h p r o b a b l y b e g i n s o p e r a t i n g when rearrangement i s almost complete,  i s only e f f e c t i v e while the i r o n - r i c h p a r t i c l e s are  s t i l l d i s p e r s e d ; i . e . w h i l e t h e d i h e d r a l angle i s z e r o . A c c o r d i n g l y , ' s o l u t i o n due t o p r e s s u r e ' c o n t i n u e s i n Stage V u n t i l t h e v a l u e o f a) f o r t h e system becomes p o s i t i v e .  The  r a t e o f the process i s i n i t i a l l y high but decreases w i t h time. The r o u n d i n g o f t h e i r o n p a r t i c l e s , w h i c h was observed i n PCM-2-20,  i s a r e s u l t o f t h e combined a c t i o n o f : a) t h e  Heavy A l l o y Mechanism, and b) ' s o l u t i o n due t o p r e s s u r e ' , w h i c h causes r e p r e c i p i t a t i o n o f s o l i d a t s u r f a c e s w h i c h a r e not under compressive  stress.  D u r i n g some i n t e r v a l i n Stage V t h e change o f d i h e d r a l angle from zero t o a p o s i t i v e v a l u e took p l a c e .  The t r a n s i t i o n  was p r o b a b l y g r a d u a l because cf> became p o s i t i v e a t f i r s t a t  119  some a r e a s , t h e n l a t e r a t o t h e r s , depending  on t h e l o c a l oxygen  c o n c e n t r a t i o n s and d i s t r i b u t i o n i n t h e compact.  Presumably,  a t t h e same time t h e c o n t a c t a n g l e was becoming p o s i t i v e and the d r i v i n g f o r c e f o r s o l u t i o n due t o p r e s s u r e was d e c r e a s i n g . The f i n a l s t a g e o f s h r i n k a g e i n Stage V was dominated by a p r o c e s s o f c o a l e s c e n c e o f t h e s o l i d p a r t i c l e s , which was p o s s i b l e once t h e d i h e d r a l a n g l e became p o s i t i v e , and w h i c h c o n t i n u e d u n t i l t h e end o f t h e runs^  E x p a n s i o n due t o d i f f u s i o n  c o n t i n u e d d u r i n g a l l o f Stage V ( i n t h e PCM-2-XX group) b u t w i t h a low and s t e a d i l y d e c r e a s i n g r a t e  (as t h e i r o n p a r t i c l e s  became s a t u r a t e d w i t h c o p p e r ) . I n t h e p r e c e d i n g d i s c u s s i o n i t has been  proposed  t h a t Stages I I I , IV and V a r e t h e r e s u l t o f t h e o p e r a t i o n o f s e v e r a l s h r i n k a g e and e x p a n s i o n mechanisms.  The d e t a i l e d  shapes o f t h e curves a r e d e t e r m i n e d by: a)  t h e a b s o l u t e r a t e s of each s h r i n k a g e and e x p a n s i o n p r o c e s s w h i l e i t i s ope r a t i n g ,  b)  t h e e x t e n t of t h e s h r i n k a g e o r cont r a c t i o n which each p r o c e s s i s c a p a b l e of p roduc i ng,  c)  t h e degree t o which t h e d i f f e r e n t p r o cesses 'overlap* in time; i . e . occur s i muItaneousIy.  Thus i t has been proposed rearrangement,  t h a t the c o n t r a c t i o n processes of  ' s o l u t i o n due t o p r e s s u r e ' and c o a l e s c e n c e o c c u r  as a c o n t i n u o u s sequence ( w i t h some p o s s i b l e o v e r l a p ) from t h e o n s e t o f m e l t i n g ( s t a r t o f Stage I I I ) t o t h e c o m p l e t i o n o f a  120  s i n t e r i n g run.  S i m i l a r l y , the overlapping expansion processes  of copper d i f f u s i o n i n t o i r o n , and g r a i n boundary p e n e t r a t i o n , may s t a r t w i t h t h e o n s e t o f copper m e l t i n g . process continues  The d i f f u s i o n  i n t o Stage V.  I f t h e above arguments a r e c o r r e c t , i t s h o u l d be p o s s i b l e t o i n t e r p r e t t h e o b s e r v e d e f f e c t o f a number o f experimental  v a r i a b l e s on t h e d i m e n s i o n a l  in liquid-phase  3.6  changes w h i c h o c c u r  sintering.  Effect of Sintering Variables 3.6.1  General  Table X I I I contains d e t a i l s of those d i l a t o m e t e r runs which were performed t o i n v e s t i g a t e t h e e f f e c t s o f s e v e r a l v a r i a b l e s on t h e p r o g r e s s  of liquid-phase s i n t e r i n g .  runs were d e s i g n e d t o be compared t o t h e s t a n d a r d each o f two p a r t i c l e s i z e s ) , PCM-2-20 and PCM-5-6.  A l l the  runs ( f o r As d i s c u s s e d  i n S e c t i o n 2.3, h e a t i n g c y c l e s o f a g i v e n type were n o t always completely  r e p r o d u c i b l e , due t o t h e v a r i a b l e and u n c o n t r o l l a b l e  response o f d i f f e r e n t compacts t o i n d u c t i o n h e a t i n g below 700°C. However, c o n s i s t e n t h e a t i n g r a t e s and h o l d i n g times were used above 700°C.  A c c o r d i n g l y , i n some samples copper m e l t e d a t  e a r l i e r t o t a l times than o t h e r s .  The d i l a t o m e t r y c u r v e s f o r  Table X I I I Runs Showing E f f e c t s o f V a r i a b l e s on L i q u i d - P h a s e S i n t e r i n g Mechanisms  Specimen  Powder Powder Holding H e a t i n g Fe/Cu ..Length o f Temperature Time a t Size of Size of Th (mins.) I r o n * * Copper** C y c l e R a t i o Run (mins.) Th, °C  Other Components •  PCM-2-20 PCM-A PCM-6 PCM-5-6 PCM-UF-2  N N N N N  78/22 78/22 78/22 78/22 78/22  122 123 55 121 124  1155 1155 1155 1155 1155  105 108 40 106 108  2 A 6 5 UF*  2 A 6 5 2  Standard U n f r a c t i o r led powder  PCM-2-10 PCM-2-19 PCM-5-13 PCM-5-12  P P P P  78/22 78/22 78/22 78/22  202 202 212 186  1155 1155 1155 1155  116 116 126 110  2 2 5 5  2 2 5 5  71 71 Mins. at E f f e c t o f 72 1000°C p r e s i n t e r i n g 62  PCM-2-23 PCM-2-24 PCM-2-25 PCM-2-30 PCM-2-100 PA-2-1 ATOCM-5  R S  78/22 7 8/22 78/22 78/22 90/10. 78/22 78/22  111 63 121 123 123 123 101  1155 1155 1110 1155 1155 1155 1155  106 33 105 107 108 108 85  2 2 2 2 2 2 5  2 2 2 2 2 2 5  heating rate heating rate 0 h o l d i n g temp, -P i n i t i a l density - o - copper c o n t e n t CD p r e a l l o y e d powder M-l Atomet 28 powder iH  N N N N N  P = Presintered  N = Normal  See T a b l e V I See T a b l e V  R = Rapid  Standard  m  W  Effect of - particle size  122  the l i q u i d - p h a s e p o r t i o n s o f runs a r e , t h e r e f o r e , b e s t compared r e l a t i v e t o t h a t p o i n t on the c u r v e s a t which the m e l t i n g copper o c c u r r e d . occurred  Where i m p o r t a n t  differences i n heating  of rates  they w i l l be noted i n the t e x t . The  Stage I I I s l o p e s quoted i n the f o l l o w i n g s e c t i o n s  were measured over the second q u a r t e r o f t h a t s t a g e .  The  Stage IV s l o p e s were measured o v e r the f i r s t t h i r d o f the  net  e x p a n s i o n i n Stage IV.  3.6.2  E f f e c t of P a r t i c l e S i z e and P a r t i c l e S i z e D i s t r i b u t i o n With decreasing  p a r t i c l e s i z e (other parameters b e i n g  h e l d e s s e n t i a l l y c o n s t a n t ) , the p r e v i o u s  d i s c u s s i o n would p r e d i c t :  A)  E a r l i e r and more r a p i d i n t r i n s i c e x p a n s i o n due t o p e n e t r a t i o n o f i r o n g r a i n b o u n d a r i e s by l i q u i d , b e c a u s e t h e g r a i n b o u n d a r i e s h a v e a smaI I e r a v e r a g e l e n g t h ( t h i s a s s u m e s t h a t the c o n c e n t r a t i o n of g r a i n b o u n d a r i e s i s e s s e n t i a l l y independent of p a r t i c l e s i z e over the range s t u d i e d ) .  B)  No e f f e c t on t h e a m o u n t o f e x p a n s i o n c a p a b l e o f b e i n g c a u s e d by g r a i n b o u n d a r y p e n e t r a t i o n ( b a s e d on t h e same a s s u m p t i o n a s i n (A') ) .  C)  More r a p i d and more e x t e n s i v e e x p a n s i o n due to d i f f u s i o n of copper i n i r o n w i t h i n Stage IV due t o t h e s h o r t e r d i f f u s i o n p a t h i n smaI Ie r pa r t i c I e s .  D)  No e f f e c t on t h e i n t r i n s i c r a t e o r extent of rearrangement s h r i n k a g e (assumes p a r t i c l e shape i s not r e l a t e d t o s i z e ) .  E)  E a r l i e r and m o r e r a p i d s h r i n k a g e by the ' s o l u t i o n due t o p r e s s u r e ' mechanism.  123  F)  More  rapid  s h r i n k a g e due  to coalescence.  G)  E a r l i e r and more e x t e n s i v e interference b e t w e e n s h r i n k a g e by r e a r r a n g e m e n t a n d e x p a n s i o n p r o c e s s e s ( f o l l o w s from (A) and (CO).  H)  A sharper transition and S t a g e V ( f o l l o w s  J)  V a r i a b l e i n t e r f e r e n c e between e x p a n s i o n p r o c e s s e s and s h r i n k a g e p r o c e s s e s ( o t h e r t h a n r e a r r a n g e m e n t ) i n l a t e S t a g e IV, dependingeon the e f f e c t s of p a r t i c l e s i z e on t h e Tetat-ive rates of the opposing processes.  b e t w e e n S t a g e IV f r o m (E) and ( F ) ) .  I n a l l t h e above p r e d i c t i o n s , i t i s assumed t h a t t h e oxygen c o n t e n t o f compacts, and i t s change w i t h s i n t e r i n g t i m e , a r e n o t s i g n i f i c a n t l y a f f e c t e d by t h e powder p a r t i c l e  size.  Runs PCM-A, PCM-2-20, PCM-5-6 and PCM-6, w h i c h i n v o l v e d n o r m a l l y - h e a t e d specimens o f d e c r e a s i n g powder p a r t i c l e s i z e , a r e d e s c r i b e d by F i g u r e s 51 tto 5:4.  Some r e l e v a n t d a t a  t a k e n from t h e d i l a t o m e t e r p l o t s a r e c o n t a i n e d i n T a b l e XIV. I t was o b s e r v e d t h a t , w i t h d e c r e a s i n g p a r t i c l e 1)  ti'  2)  size:  The r a t e and amount o f n e t s h r i n k a g e observed i n Stage III decreased. This is c o n s i s t e n t with p r e d i c t i o n (G). Moreo v e r , the f o r m a t i o n of e-phase j u s t above the m e l t i n g p o i n t of copper might be m o r e c o m p l e t e w i t h f i n e r p o w d e r s b e f o r e t h e p e r i t e c t i c t e m p e r a t u r e was r e a c h e d . Because t h a t r e d u c e s t h e amount o f liquid a v a i l a b l e to the system f o r a small interval of t i m e , i t might a l s o p a r t i a l l y account f o r the lower i n i t i a l sate of Stage I1 1 s h r i n k a g e w i t h f i n e r powder s p e c i m e n s . The r a t e and amount o f e x p a n s i o n i n S t a g e IV f i r s t i n c r e a s e d ( b e t w e e n PCM-A a n d PCM-2-20), and t h e n d e c r e a s e d , ( c o n s i s t e n t  F i g u r e 52.  D i l a t o m e t e r p l o t f o r Run PCM-A. (Normal h e a t i n g , 22% copper, 105 t o 120y powders)  %  A L / L  0  F i g u r e 54.  D i l a t o m e t e r p l o t f o r Run PCM-6. (Normal h e a t i n g , 22% copper, <25u powders.)  T a b l e XIV E f f e c t o f P a r t i c l e S i z e and P a r t i c l e S i z e D i s t r i b u t i o n on t h e D i m e n s i o n a l Changes o f Compacts D u r i n g L i q u i d - P h a s e S i n t e r i n g Sample  PCM« A  PCP.eM-AO  Powder S i z e  microns  A  % (AL/Lo)  +1.87  B  %(AL/Lg)  -  C  %(AL/Lo)  -2.02  D  %(AL/Lo)  -  105  to  .30  .15  120  PCM-2-20  to  53  63  +1.35  PCM-5-6  to  25  37  + 1.30 +  .22  -1.67  -  .95  +1.62  +1.02  -  .35  PGM°-"6r <25  +1.22 0  - PCM-UF-2 see Table X I I I +1.30 -  .10 .95  -  .75  -  +  .20  +1.60  B to C  %(AL/Lo)  1.72  1.32  1.17  .75  .85  C to D  %(AL/Lo)  1. 87  3.29  1.97  .95  2.55  .4  Slope I I I  [%(AL/Lo)]/min  -2.5  -2.0  -1.8  -  S l o p e IV  [% (AL/Lo)]/min  + 1.0  +1.8  +1.5  +1.0  -1.3 +1.5  128  with p r e d i c t i o n J above). With t h e c o a r s e s t powder i n t h e s e r i e s , t h e rates of the expansion processes are so low r e l a t i v e t o t h o s e o f c o n t i n u i n g contraction processes that the rate and n e t e x t e n t o f o b s e r v e d expansion i n S t a g e IV a r e b o t h s m a l l . With very f i n e p o w d e r s , both e x p a n s i o n and c o n t r a c t i o n processes are rapid. This leads t o e a r l y i n t e r a c t i o n between t h e o p p o s i n g p r o c e s s e s , and a s h a r p t r a n s i t i o n b e t w e e n S t a g e s IV a n d V . 3)  The r a t e s o f n e t c o n t r a c t i o n throughout Stage V were h i g h e r , c o n s i s t e n t w i t h p r e d i c t i o n s ( E ) and ( F ) a b o v e .  Specimen PCM-UF-2 was p r e p a r e d from u n f r a c t i o n e d i r o n powder, i t c o n t a i n e d p a r t i c l e s b o t h c o a r s e r and f i n e r t h a n t h o s e o f PCM-2-20 and PCM-6, r e s p e c t i v e l y  (see T a b l e V I ) .  The  response o f t h e specimen t o l i q u i d - p h a s e s i n t e r i n g , which i s shown i n F i g u r e 55 and T a b l e XIV, was g e n e r a l l y i n t e r m e d i a t e between t h a t o f specimens  PCM-5-6 and PCM-2-20; i . e . t h e specimen  behaved e s s e n t i a l l y as though i t had an average p a r t i c l e  size  of 37 t o 53 m i c r o n s .  3.6.3  Effect of Presintering  Another group o f Fe-22 Cu specimens, PCM-5-12, PGM-5-13 , PCM-2-10, and PCMS2--19 ,-were>heated u s i n g the p r e s i n t e r i n g c y c l e o f F i g u r e 15, i n c o r p o r a t i n g a p e r i o d o f r o u g h l y one hour a t 1000°C.  The d i l a t o m e t r i c r e s u l t s a r e i n F i g u r e s 56 t h r o u g h  59 and t h e d a t a a r e summarised i n T a b l e XV.  2 o " 0 1  1  1  1  1  20  40  l  I  60  I  Time  F i g u r e 55.  l  80  — I  I  100  I  i  120  (min)  D i l a t o m e t e r p l o t f o r Run PCM-UF-2. (Normal h e a t i n g , 22% copper, u n f r a c t i o n e d i r o n powder.)  1  1  —  140  130  3. CN r o  H  o  I  LT) +J  I  s m U CN  04 3  Pi 04  uo c ou E ^ +J CN  E i-  O CN H D-. T3 M OJ OJ M - P OJ —> 0J +J • S A W O - H 5-1 4-> W OJ CO OJ TS H M £ • H P-i O Q O. w  in OJ  u •iH  &4  °-|/~lV %  powders.)  2.0 h  < - I.Oh  -2.0  80  100 Time  Figure  58.  120  140  (min)  D i l a t o m e t e r p l o t f o r Run PCM ( P r e s i n t e r e d , 22% c o p p e r , 53 powder.) ( S p u r i o u s data)  2.0h  .0  0  0  20  40  60  •  •  80  I  I  I  100  Time  Figure  59.  I  120  I  I  I  140  (min)  D i l a t o m e t e r p l o t f o r Run PCM-2-19. ( P r e s i n t e r e d , 22% c o p p e r , 53 t o 63u powder.)  1—  160  134  T a b l e XV E f f e c t o f P r e s i n t e r i n g on D i m e n s i o n a l Changes o f Compacts D u r i n g L i q u i d - P h a s e S i n t e r i n g  Sample  PCM-2-10 PCM-2-19 PCM-5-13 PCM-5-12  Powder s i z e  microns  A  %(AL/Lo)  + 1.25  +1.37  +1.32  +1.25  B  %(AL/Lo)  -1.22  -1.52  -1.25  -1.13  C  %(AL/Lo)  -1.50  -1. 64  -1.35  -1.35  D  %(AL/Lo)  +1.25  +1.40  - .11  + .45  B to C  %(AL/L o)  .28  .12  .10  .22  C to D  %(AL/Lo)  2.75  3.04  1.24  1.80  Slope I I I  [%(AL/Lo)]/min  - .3  - .1  - .1  - .3  S l o p e IV  [%(AL/Lo)]/min  +1.0  +1.0  +1.2  • + .7  53 t o 63 53 t o 63 25 t o 37 25 t o 37  135  A l l t h e s e specimens e x p e r i e n c e d s u b s t a n t i a l s t a t e s i n t e r i n g s h r i n k a g e a t 1000°C.  solid-  A t t h e end o f Stage I I ,  a l l underwent s l i g h t t h e r m a l e x p a n s i o n as t h e t e m p e r a t u r e was i n c r e a s e d t o 1070°C.  A f t e r t h e o n s e t o f copper m e l t i n g , t h e  d i l a t o m e t r i c b e h a v i o u r was s i m i l a r t o t h a t o f specimens p r e v i o u s l y d i s c u s s e d , w i t h t h e n o t a b l e e x c e p t i o n t h a t Stage I I I was v e r y s m a l l . Specimens PCM^5-12 and PCM-5-13 were h e l d a t 1000°C f o r 62 minutes and 74 minutes r e s p e c t i v e l y .  I n method o f  p r e p a r a t i o n and p r o c e s s i n g , they were o t h e r w i s e i d e n t i c a l t o PCM-5-6 ( F i g u r e 56 and T a b l e XIV) w h i c h was h e l d a t 1000°C f o r only three minutes.  Comparing t h e s i n t e r i n g b e h a v i o u r o f t h e  t h r e e specimens a f t e r copper m e l t e d , i t i s seen t h a t w i t h i n c r e a s e d p r e s i n t e r i n g a t 1000°C: A)  S t a g e I I I s h r i n k a g e was a lower r a t e .  B)  Stage  C)  T h e r a t e o f S t a g e IV e x p a n s i o n was l o w e r ( c o m p a r i n g t h e a v e r a g e o f PCM-5-12 and PCM-5-13 w i t h t h a t o f P C M - 5 - 6 ) .  IV e x p a n s i o n  was  smaller  less  and had  extensive.  E x a c t l y t h e same t r e n d s a r e seen when specimens PCM-2-10 and PCM-2-19 a r e compared w i t h t h e i r n o n - p r e s i n t e r e d e q u i v a l e n t , PCM-2-20. One o f t h e consequences o f l o n g e r p r e s i n t e r i n g a t 1000°C i s t h a t more s u b s t a n t i a l necks a r e e s t a b l i s h e d a t i r o n iron p a r t i c l e contacts.  That d e l a y s t h e rearrangement p r o c e s s  136  i n Stage I I I , by i n c r e a s i n g the time r e q u i r e d f o r molten copper to p e n e t r a t e the necks of the s o l i d - s t a t e s i n t e r e d  skeleton.  Soon a f t e r rearrangement i s underway, the r a t e of the expansion processes i s h i g h , and Stage IV  (net expansion) s t a r t s b e f o r e  much rearrangement shrinkage i s observed.  However, r e a r r a n g e -  ment i s b a s i c a l l y a r a p i d s h r i n k a g e p r o c e s s and i t s d e l a y e d , but c o n t i n u e d , o p e r a t i o n i n Stage IV has the e f f e c t of r e d u c i n g the Stage IV s l o p e , as w e l l as reducing the amount of net expansion which i s seen i n Stage IV. The observed e f f e c t s of p r e s i n t e r i n g are a l l thus s a t i s f a c t o r i l y e x p l a i n e d , i n terms of a delay i n the onset of rearrangement s h r i n k a g e . Another e f f e c t o f l o n g e r p r e s i n t e r i n g s h o u l d be t o remove more o f the r e s i d u a l oxygen i n the compact b e f o r e l i q u i d - p h a s e s i n t e r i n g processes b e g i n to o p e r a t e . r e s u l t i n the attainment of a p o s i t i v e  That should  (non-zero) d i h e d r a l  angle i n the system a t an e a r l i e r time a f t e r m e l t i n g ( i . e . e a r l i e r i n Stage V) and a p o s s i b l e r e d u c t i o n i n the r a t e o f Stage V s h r i n k a g e . was  That p r e d i c t e d e f f e c t , i f p r e s e n t a t a l l ,  small. However, i f the oxygen content of the p r e s i n t e r e d  compacts was  s i g n i f i c a n t l y lower than t h a t of n o n - p r e s i n t e r e d ,  e q u i v a l e n t specimens a t the onset o f m e l t i n g , i t  i s also  p o s s i b l e t h a t the aforementioned delay i n the s t a r t of Stage III  (and i t s subsequent i n f l u e n c e on Stage IV) i s due t o the  137  i n c r e a s e i n t h e l i q u i d u s temperature o f Cu-0 a l l o y s w i t h dec r e a s i n g oxygen c o n t e n t .  The e f f e c t o f lower oxygen c o n t e n t  would be t o cause m e l t i n g t o o c c u r over a l a r g e r range o f temperature; i . e . t h e amount o f l i q u i d i n t h e system would i n c r e a s e more g r a d u a l l y as t h e temperature was i n c r e a s e d above 1065-1070°C.  3.6.4  E f f e c t o f H e a t i n g Rate and H o l d i n g  Temperature  F i g u r e s 6 0 and 61 and T a b l e XVI (samples PCM-2-20, PCM-2-23 and PCM-2-24) show t h e e f f e c t s o f h e a t i n g r a t e on t h e p r o g r e s s o f l i q u i d - p h a s e s i n t e r i n g i n FE-22Cu ' specimens. o t h e r r e s p e c t s , t h e t h r e e samples were e s s e n t i a l l y  In  identical,  i n terms o f method o f p r e p a r a t i o n and p r o c e s s i n g . The f o l l o w i n g o b s e r v a t i o n s accompanied  more r a p i d  h e a t i n g o f t h e compacts: i)  Stage  I I I s h r i n k a g e was m o r e  extensive.  ii)  The r a t e higher.  of Stage  111  iii)  The r a t e higher.  of Stage  IV e x p a n s i o n  iv)  The amount o f S t a g e s i i ghtIy reduced.  O b s e r v a t i o n s i ) and i i )  shrinkage  was  was  IV e x p a n s i o n  was  can be p a r t l y e x p l a i n e d i n  terms o f e-phase f o r m a t i o n . A h i g h e r h e a t i n g r a t e d e c r e a s e s t h e t i m e t h e compacts spend i n t h e temperature range i n w h i c h e-phase forms.  T h e r e f o r e t h e amount o f l i q u i d a v a i l a b l e e a r l y  2.0  Figure  60.  D i l a t o m e t e r p l o t f o r Run PCM-2-23. (Rapid h e a t i n g , 22% copper, 53 t o 63y powders.)  F i g u r e 61.  D i l a t o m e t e r p l o t f o r Run PCM-2-24. (Slow h e a t i n g , 22% copper, 53 t o 631% powders.) The dashed curve shows the r e s u l t s - f o r Run PCM-2-20.  140  Table X V I E f f e c t o f H e a t i n g Rate and H o l d i n g Temperature on D i m e n s i o n a l Changes D u r i n g L i q u i d - P h a s e S i n t e r i n g  Sample  PCM-2-23 P C M - 2 - 2 0  Heating rate Holding temperature  Rapid  PCM-2-24  PCM-2-25  Normal  Slow  Normal  degrees centigrade  1155  1155  1155  1110  A  % ( A L / L o)  + 1.30  +1.35  +1.30  +1.35  B  %(AL/Lo)  +  -  -  -  C  %(AL/Lo)  -1.25  -1.67  -1.62  -1.30  D  %(AL/L )  +1.35  +1.62  +1.65  +2.02  B toC  %(AL/L )  2.02  1.32  1.07  1. 0 3  C toD  %(AL/L )  2.60  3.29  3.27  3.32  Slope  0  III  ;Slope I V  0  0  .77  .35  .55  [% ( A L / L o ) ] / m i n  -4.5  -1.5  -  [%(AL/LQ)]/min  + 2.7  +1.7  +1.5  .6  .27  -1.0  +2.3  141  i n Stage I I I i s i n c r e a s e d by more r a p i d h e a t i n g .  A l s o , because  the e x p a n s i o n p r o c e s s e s a r e d i f f u s i o n c o n t r o l l e d , whereas rearrangement  i s not, at high rates of heating i t i s possible  f o r more rearrangement  to occur before the expansion processes  are r a p i d enough t o p r o v i d e a p p r e c i a b l e i n t e r f e r e n c e .  However,  s h r i n k a g e p r o c e s s e s which i n v o l v e s o l u t i o n p r e c i p i t a t i o n a r e slow compared t o g r a i n boundary p e n e t r a t i o n . Thus w i t h h i g h h e a t i n g r a t e s , more r a p i d e x p a n s i o n i s 'seen' i n Stage IV because t h e r e i s l e s s s i m u l t a n e o u s s h r i n k a g e . In the f a s t - h e a t e d  sample t h e r e i s i n s u f f i c i e n t  time f o r much e x p a n s i o n due t o d i f f u s i o n t o o c c u r b e f o r e Stage IV ended.  Thus, l e s s n e t e x p a n s i o n i s 'seen'  ( i n Stage IV)  f o r t h a t r u n t h a n f o r t h e s l o w e r - h e a t e d samples.  Because more  e x p a n s i o n by d i f f u s i o n remained t o o c c u r i n Stage V f o r t h e f a s t heated specimen, i t e x h i b i t e d a lower n e t r a t e o f s h r i n k a g e i n Stage V. Run PCM-2-25 was made w i t h a f i n a l h o l d i n g temperature o f 1110°C i n s t e a d o f 1155°C.  Comparison  o f Runs PCM-2-25 and  PCM-2-20 (see F i g u r e 62 and T a b l e XVI) shows t h e d i f f e r e n c e i n s i n t e r i n g behaviour. The d i f f e r e n t r a t e s o f s h r i n k a g e i n Stage I I I were due t o a s l i g h t l y lower h e a t i n g r a t e above t h e m e l t i n g p o i n t i n PCM-2-25.  The major d i f f e r e n c e between the two c u r v e s i s  t h a t t h e amount o f Stage I I I s h r i n k a g e i s l e s s i n t h e sample heated^ t o 1110°C.  A p o s s i b l e cause i s t h a t more e-phase was  F i g u r e 62.  D i l a t o m e t e r p l o t f o r Run PCM-2-25. (Normal h e a t i n g , 22% copper, h e l d a t 1110°C.) The dashed curve shows the r e s u l t s f o r Run PCM-2-20.  ^ ^  143  formed i n t h e more s l o w l y h e a t e d sample  (PCM-2-25),  thus l e s s  l i q u i d was a v a i l a b l e f o r t h e rearrangement p r o c e s s . The s l i g h t l y  l o w e r r a t e o f Stage V s h r i n k a g e i n t h e  sample h e a t e d t o 1110°C was l i k e l y due t o l e s s r a p i d c o a l e s c e n c e because o f l o w e r d i f f u s i o n r a t e s .  3.6.5  Effect of I n i t i a l  Density  Comparison o f Runs PCM-2-30 and PCM-2-20  (see F i g u r e  63) and T a b l e XVII) shows t h e e f f e c t o f i n i t i a l compact d e n s i t y on s i n t e r i n g b e h a v i o u r .  A l t h o u g h o t h e r w i s e s i m i l a r t o PCM-2-20  i n method o f p r e p a r a t i o n and p r o c e s s i n g , PCM-2-30 was to a much h i g h e r i n i t i a l d e n s i t y  compacted  (85%, v e r s u s 71% o f t h e o r e t i c a l  after cleaning). The more dense specimen c o n t r a c t e d much l e s s i n Stage I I I , w h i c h would be e x p e c t e d because t h e r e was l e s s p o s s i b i l i t y o f accommodation  by t h e rearrangement p r o c e s s .  The  r a t e s o f s h r i n k a g e i n Stage I I I and o f e x p a n s i o n i n Stage I V were e s s e n t i a l l y independent o f t h e s t a r t i n g d e n s i t y . I t was o b s e r v e d t h a t f o r t h e more dense PCM-2-30, c o n t r a c t i o n was i n i t i a l l y  specimen,  more r a p i d i n Stage V.  A s s o c i a t e d w i t h t h a t was t h e s h a r p e r t r a n s i t i o n between IV and V. the  I t i s speculated that these e f f e c t s are r e l a t e d t o  stage i n s i n t e r i n g a t which y  of oxygen from t h e system. by hydrogen  Stages  S L  i s i n c r e a s i n g due t o removal  The denser compact i s p e n e t r a t e d  ( i n t h e d i l a t o m e t e r ) w i t h more d i f f i c u l t y .  Water  JL  0  20  40  _L  60  J  80  Time  ^JL  100  ~--l20  (min)  F i g u r e 63. D i l a t o m e t e r p l o t f o r Run PCM-2-30. (Normal h e a t i n g , 22% copper, h i g h i n i t i a l d e n s i t y . ) The dashed curve shows t h e curve f o r Run PCM-2-20.  140  145  Table XVII E f f e c t o f I n i t i a l D e n s i t y on D i m e n s i o n a l Changes During Liquid-Phase S i n t e r i n g  Sample  PCM-2-30  Initial density (p )  PCM-2-20  gm/cc  6.81  5.74  A  %(AL/Lo)  +1.30  +1.35  B  %(AL/Lo)  +  .20  -  C  %(AL/Lo)  -  .16  -1.67  D  %(AL/Lo)  + 3.22  +1. 62  to e  %(AL/Lo)  .36  1.32  C to D  %(AL/Lo)  3.38  3.29  c  B  .35  Slope I I I  [%(AL/LQ)]/min  -1.4  -1.5  Slope I V  [%(AL/Lo)]/min  +1.6  +1.7  146  vapour produced by t h e r e d u c t i o n o f o x i d e s a t i n t e r n a l pores a l s o f i n d s i t more d i f f i c u l t t o escape from t h e denser compact. Thus, i t i s suggested t h a t t h e major i n c r e a s e i n y„  T  (which  fail  causes t h e d i h e d r a l a n g l e t o become > 0) o c c u r r e d a t a l a t e r time i n Stage V f o r PCM-2-30 t h a n f o r PCM-2-20. Once t h e d i h e d r a l a n g l e has become p o s i t i v e , s h r i n k a g can proceed o n l y by c o a l e s c e n c e .  The c o a l e s c e n c e p r o c e s s i s  expected t o be more r a p i d i n a lower d e n s i t y compact. l a t e r i n Stage V t h e lower d e n s i t y specimen  Thus,  i s observed t o  s h r i n k more r a p i d l y .  3.6.6  E f f e c t o f Copper Content Sample PCM-2-100 c o n t a i n e d 10% copper and had a  compacted d e n s i t y which was 2.9% (of t h e o r e t i c a l ) h i g h e r t h a n t h a t o f PCM-2-20  (which c o n t a i n e d 22% c o p p e r ) .  Comparison o f  F i g u r e s 51 and 64 and T a b l e X V I I I i n d i c a t e s t h a t t h e sample with less  copper: I) ii)  Contracted  less  C o n t r a c t e d more  i n Stage I I I slowly  iii)  Expanded  less  iv)  Expanded  more s l o w l y  v)  Contracted  i n Stage  much  less  i n Stage I I I IV  i n Stage slowly  IV  i n Stage  V  A l l o f t h e s e o b s e r v a t i o n s a r e c o n s i s t e n t w i t h mechanisms proposed e a r l i e r .  W i t h l e s s l i q u i d phase p r e s e n t , v o i d s  w i t h i n t h e l i q u i d a r e l a r g e r and t h e d r i v i n g f o r c e f o r s h r i n k a g  2.0  J  L _ 140  Time  F i g u r e 64.  (min)  D i l a t o m e t e r p l o t f o r Run PCM-2-100. (Normal h e a t i n g , 10% copper.)  £  148  Table XVIII E f f e c t o f Copper Content on D i m e n s i o n a l Changes During L i q u i d f P h a s e i S i n t e r i n g . *  Sample Copper  PCM-2-1000 %  PCM-2-20  10  22  A  %(AL/Lo)  +1.30  +1.35  B  %(AL/Lo)  +  .70  -  C  %(AL/Lo)  -  .10  -1.67  D  % (AL/Lo)  +1.53  +1.62  B to C  %(AL/L )  .60  1.32  C to D  %(AL/Lo)  1.63  3.29  Slope I I I : S l o p e IV  0  .35  [%(AL/Lo)/min]  -1.6  -1.5  [% ( A L / L ) / m i n ]  +  +1.7  0  .7  149  by rearrangement o r s o l u t i o n due  to pressure i s decreased.  With l e s s l i q u i d to d i s t r i b u t e at p a r t i c l e p e n e t r a t e d g r a i n boundaries would e x p e c t :  "contacts', i n  and over p a r t i c l e s u r f a c e s , one  a) l e s s growth due t o g r a i n - b o u n d a r y  b) l e s s shape-change o f p a r t i c l e s by the  penetration,  solution-precipitation  p r o c e s s , and c) a h i g h e r e f f e c t i v e v i s c o s i t y i n the  solid-liquid  aggregate. I t s h o u l d be noted t h a t i n PCM-2-100 t h e r e was 10% l i q u i d a t the o n s e t o f m e l t i n g .  As copper d i f f u s e d  the i r o n , the amount o f l i q u i d d e c r e a s e d .  only into  I n e a r l y Stage V,  the amount o f l i q u i d would have become reduced  t o <9%  by  weight  and the v e r y low n e t r a t e o f c o n t r a c t i o n i n t h a t s t a g e i s easily  understood.  3.6.7  E f f e c t o f a D i f f e r e n t Type o f I r o n Powder Sample ATOCM-5 c o n t a i n e d Atomet 28 i r o n , whereas  PCM-5-6, which was way,  otherwise prepared  and p r o c e s s e d i n the same  c o n t a i n e d Eastono^iron powderj i^r Comparison-of the two runs  (see  T a b l e XIX and F i g u r e s 53 and 65) i n d i c a t e s t h a t t h e Atomet i r o n compact expanded l e s s i n Stage IV and, c o n t r a c t e d l e s s r a p i d l y i n Stage V.  I n o t h e r r e s p e c t s the d i l a t o m e t r i c c u r v e s ,  f o r the two specimens, were s i m i l a r . Based on m e t a l l o g r a p h i c o b s e r v a t i o n s the Atomet 28 powder p a r t i c l e s were i n i t i a l l y more r e g u l a r i n shape. may  have c o n t a i n e d fewer g r a i n b o u n d a r i e s , a t the  They  sintering  150  T a b l e XIX E f f e c t o f Powder Type on D i m e n s i o n a l Changes D u r i n g L i q u i d Phase S i n t e r i n g  Sample I r o n powder type A  % (AL/Lo)  B  PCM-5-6  ATOCM-5  Easton  Atomet 28  +1.30  +1.30  + .22  - .10  C  %(AL/Lo)  - .95  -1.27  D  %(AL/Lo)  +1.02  + .15  B to C  %(AL/Lo)  1.17  1.17  C to D  %(AL/Lo)  1.97  1.42 *  Slope I I I  [%(AL/Lo)]/min  -2.0  - .7  Slope  [%(AL/Lo)]/min  +1.5  +1.4  IV  *  Not i n d i c a t i v e o f average r a t e i n Stage I I I .  I  0  1  1 20  Figure 65.  I  I  40  I  I  60  I  I  80  I  I  I  100  Time (min) D i l a t o m e t e r p l o t f o r Run ATOCM-5. (Normal h e a t i n g , 25 t o 37y Atomet i r o n powderi)  -I  120  152  t e m p e r a t u r e , t h a n t h e e q u i v a l e n t E a s t o n powder p a r t i c l e s .  That  c o u l d e x p l a i n a s m a l l e r amount o f e x p a n s i o n by g r a i n boundary penetration  i n Stage I V .  I t i s also b e l i e v e d that the Easton  powder was more e x t e n s i v e l y fragmented by l i q u i d i n Stage I I I , p r o v i d i n g a h i g h e r d e n s i t y o f s m a l l p a r t i c l e s (and a h i g h e r shrinkage  rate) f o r s o l u t i o n - p r e c i p i t a t i o n processes i n l a t e r  stages.  3.6.8  Use o f P r e a l l o y e d Powder Sample PA-2-1 was p r e p a r e d from p r e a l l o y e d i r o n powder  c o n t a i n i n g 6.9% copper.  S u f f i c i e n t pure copper powder was  added t o b r i n g t h e Fe/Cu r a t i o i n t h e compact t o 78/22. p a r i s o n o f PA-2-1 w i t h PCM-2-20 (see F i g u r e s  Com-  66 and 51) shows  the e f f e c t o f p r e a l l o y e d i r o n on t h e p r o g r e s s o f l i q u i d - p h a s e sintering.  PCM-2-20 and PA-2-1 c o n t a i n e d  t h e same s i z e o f  powders. R e l a t i v e t o PCM-2-20, t h e p r e a l l o y e d i r o n powder specimen r e a r r a n g e d more e x t e n s i v e l y i n Stage I I I and e x h i b i t e d a l m o s t no Stage IV e x p a n s i o n .  The n e t c o n t r a c t i o n r a t e i n  Stage V was a l s o v e r y low. ThoseobbservationsaaiL=eceonsistehtwwithtthe~ f o l l o w i n g : i)  Because the Iron i s nearly saturated w i t h copper from t h e b e g i n n i n g , there is l i t t l e f l u x of copper across the liquid-solid interface. As a r e s u l t , oxygen present i n the l i q u i d copper  2.0  154  d o e s n o t become s e g r e g a t e d a t t h e i n t e r face. The d i h e d r a l a n g l e a c c o r d i n g l y rema i n s p o s i t i v e . ii)  iii)  iv)  Because of ( i ) , g r a i n boundary p e n e t r a t i o n , and t h e e x p a n s i o n a s s o c i a t e d w i t h i t cannot occur. F u r t h e r , t h e amount o f e x p a n s i o n p o s s i b l e by v o l u m e d i f f u s i o n is very limited. Extensive rearrangement, i n Stage I I I , is p o s s i b l e because of the near t o t a l a b s c e n c e .of i n t e r f e r e n c e f r o m e x p a n s i o n p rocesses. Beyond Stage I I I , t h e o n l y s h r i n k a g e mechanism a v a i l a b l e i s c o a l e s c e n c e . Thus t h e r a t e of o b s e r v e d s h r i n k a g e i s very low.  Chapter  4  COMPARISON WITH PREVIOUS WORK 4.1  Comparison w i t h t h e R e s u l t s o f K i n g e r y A s t r i k i n g o b s e r v a t i o n i n t h i s work was  (up t o 2.02%  (AL/Lo)) and r a p i d s h r i n k a g e o f Fe-Cu compacts  which occurred immediately  f o l l o w i n g m e l t i n g o f copper,  l a r l y i n n o n - p r e s i n t e r e d specimens. log  the e x t e n s i v e  particu-  F i g u r e 67 c o n t a i n s l o g -  p l o t s o f Stage I I I d a t a f o r s e v e r a l compacts, i n c l u d i n g  t h o s e w h i c h e x h i b i t e d t h e l o w e s t and h i g h e s t r a t e s o f s h r i n k a g e . The  change i n l e n g t h ( A L ) ,of<fa specimen, as a p e r c e n t a g e  the l e n g t h , L / Q M  of  a t the o n s e t o f m e l t i n g , has been p l o t t e d  a g a i n s t ( t - t ) , the time i n t e r v a l a f t e r m e l t i n g o c c u r r e d .  In  m  o b t a i n i n g l e n g t h v a l u e s from the d i l a t o m e t r i c d a t a a c o r r e c t i o n was made f o r the t h e r m a l e x p a n s i o n which o c c u r s as a specimen i s heated above 1070°C i n Stage I I I . The The  c o r r e c t i o n was  l o g - l o g p l o t s of the data g i v e s t r a i g h t  w i t h s l o p e s r a n g i n g from 0.80  t o 1.50  small.  lines  f o r the e a r l y p a r t s of  Stage I I I . I f i t i s assumed t h a t t h e r e i s a s i n g l e dominant ( c o n t r a c t i o n ) p r o c e s s o p e r a t i n g e a r l y i n Stage I I I , then the k i n e t i c s o f t h a t p r o c e s s are r e p r e s e n t e d 155  by:  156  F i g u r e 67.  Log f r a c t i o n a l change i n l e n g t h o f compacts ( r e l a t i v e t o L , the l e n g t h a t m e l t i n g ) , Q M  v versus l o g ( ) / the time from m e l t i n g , d u r i n g Stage I I I s h r i n k a g e . t _ t  m  157  AL/Lo = 1/3(AV/Vo) = k t  (4.1)  n  where n = (1.15 + 0.35). The r e s u l t s a r e c o n s i s t e n t w i t h t h e p r e d i c t i o n s o f Kingery's model f o r s h r i n k a g e by rearrangement.  Other  sintering  s h r i n k a g e mechanisms g i v e v a l u e s o f t h e t i m e exponent, n, r a n g i n g from 0.2 t o 0.5.  I t may  t h e r e f o r e beareas.bhabl>y c o n c l u d e d  t h a t t h e p r o c e s s o f rearrangement dominated Stage I I I b e h a v i o u r . F o r a number o f l i q u i d - p h a s e s i n t e r i n g system, o t h e r t h a n Fe-Cu, Eremenko [6] has r e p o r t e d v a l u e s o f n r a n g i n g from 1 t o 3 f o r the f i r s t s t a g e o f c o n t r a c t i o n , w h i c h he i d e n t i f i e d as rearrangement. Kingery  [3] s i n t e r e d 7 8/22 Fe-Cu powder m i x t u r e s based  on i r o n powders o f <35u  m  i n d i a m e t e r , a t 1150°C.  contains Kingery's log-log p l o t s of h i s r e s u l t s .  Figure 6 Because  the  s l o p e s o f t h e p l o t s i n t h e e e a r l y ' s t a g e s o f s i n t e r i n g were i n the range 1.3 t o 1.4, K i n g e r y c o n c l u d e d t h a t he was o b s e r v i n g s h r i n k a g e due t o rearrangement. f o r the 15.8 and 3 3 . 1 y  m  His e a r l i e s t observations  powders were 'at 10 m i n u t e s ' .  i t i s n o t c l e a r from h i s p u b l i s h e d work [14] whether was  However that  10 minutes a f t e r m e l t i n g , o r a f t e r the a t t a i n m e n t o f 1150°C  i n t h e specimen. F i g u r e 68 shows the d i l a t o m e t r i c p l o t from t h e p r e s e n t work f o r Run PCM-6, w h i c h a l s o c o n t a i n e d 2 5 u <  m  powder p a r t i c l e s .  The o n s e t of m e l t i n g i s shown as t ; t h e t e m p e r a t u r e reached 1155°C a t t . s  Ten minutes a f t e r t , t h e specimen i s a t t , , ; m , ±K  158  _L  0  JL  20 Time  F i g u r e 68.  40 (min)  60  D i l a t o m e t e r curve f o r Run PCM-5-6. The d o t t e d l i n e shows p r e d i c t e d d i m e n s i o n a l changes i f Stage IV e x p a n s i o n d i d not o c c u r .  159  i . e . a l r e a d y a t t h e s t a r t of Stage V c o n t r a c t i o n . more by t  l  k  Further-  the specimen has a l r e a d y undergone net s h r i n k a g e  r e l a t i v e to i t s o r i g i n a l  (as-cleaned) room-temperature s i z e .  Because K i n g e r y based volume o r d e n s i t y changes on as-compacted ('green') measurements, he would see c o n t r a c t i o n ( d e n s i f i c a t i o n ) a t the e q u i v a l e n t o f t i m e t ^ i n a specimen comparable t o PCM-6. I n f a c t , i t i s more l i k e l y t h a t K i n g e r y ' s time base was  the  a t t a i n m e n t o f 1150°C ( i n h i s specimens) i n which case h i s f i r s t o b s e r v a t i o n would have been even l a t e r i n Stage V t h a n t ^ . I t i s t h e r e f o r e reasonable t o conclude t h a t Kingery, perhaps by v i r t u e o f h i s d i l a t o m e t r i c t e c h n i q u e , c o m p l e t e l y f a i l e d t o d e t e c t the Stage I I I c o n t r a c t i o n and t h e Stage e x p a n s i o n o b s e r v e d i n t h e p r e s e n t work.  IV  I t further follows  t h a t h i s l o g - l o g p l o t s , as i n d i c a t o r s o f the p r o c e s s e s o c c u r r i n g during l i q u i d - p h a s e s i n t e r i n g , are meaningless.  The  dimensional,  o r d e n s i t y changes p l o t t e d f o r a g i v e n time a r e t h e r e s u l t o f the c u m u l a t i v e e f f e c t o f the s e v e r a l p r o c e s s e s which have o p e r a t e d up t o t h a t t i m e . I t i s p o s s i b l e t o make rough c o r r e c t i o n s t o K i n g e r y ' s d a t a w h i c h remove t h e e f f e c t s o f Stage IV e x p a n s i o n l i n e F i g u r e 68).  (dotted  On t h e b a s i s o f observed e x p a n s i o n i n PCM-6  an a d d i t i o n o f 0.038 (AV/V-'o) has been made t o t h e amount o f s h r i n k a g e a t each o f K i n g e r y " s d a t a p o i n t s f o r a 1 5 . 8 y specimen.  m  powder  The r e s u l t s a r e shown i n F i g u r e 69, a p l o t o f t h e  o r i g i n a l and  'corrected' data.  The c o r r e c t e d c u r v e , which  160  1.000  •  1  1  1  1  1  r—  0.500  > < c  ~ o  0.100  -  0.050  •  0.020  •  •  AV  /  /  -  /  0.010 -  •  22.0 % Cu 15.8 f~Lm  0.005 0.002 •  • 5 Time  i 10  • 20  From  i  50  1 »— 100 200  500  Melting (min)  F i g u r e 69. K i n g e r y ' s d a t a f o r f r a c t i o n a l d e n s i f i c a t i o n v e r s u s s i n t e r i n g t i m e ( s o l i d l l i n e ) and t h e same d a t a c o r r e c t e d t o e l i m i n a t e t h e e f f e c t of Stage IV e x p a n s i o n ( d o t t e d l i n e ) . The c o r r e c t i o n was based on t h e r e s u l t s f o r <25u powder i n t h e p r e s e n t work.  161  s h o u l d r o u g h l y i n d i c a t e t h e mechanisms c a u s i n g s h r i n k a g e i n K i n g e r y ' s specimen, shows two p o r t i o n s .  The f i r s t has a s l o p e  o f 3/4, which i s between t h e v a l u e s o f n f o r rearrangement and ' s o l u t i o n due t o p r e s s u r e ' . However, even t h e c o r r e c t e d curve has q u e s t i o n a b l e meaning.  The time base o f t h e p l o t may f a r from c o i n c i d e w i t h  the s t a r t of the p a r t i c u l a r shrinkage process t h a t i s o p e r a t i n g d u r i n g t h e time range o f t h e d a t a i n F i g u r e 69, even i f o n l y one such p r o c e s s i s i n v o l v e d . I t s h o u l d be noted t h a t K i n g e r y used t h r e e i r o n powders i n h i s Fe-Cu e x p e r i m e n t s , two o f which were d e s c r i b e d o n l y as "magnetic i r o n powder" [ 1 4 ] .  The c o m p o s i t i o n o f t h e  powders was n o t g i v e n , b u t "magnetic"  i r o n powders t y p i c a l l y  c o n t a i n 0.6 t o 1.0 p e r c e n t carbon. 1.5.5 and elsewhere  As d i s c u s s e d i n S e c t i o n  i n t h i s c h a p t e r , carbon a d d i t i o n s t o  Fe-Cu compacts can r e d u c e , o r e l i m i n a t e , t h a t l a r g e component o f e x p a n s i o n w h i c h i s a s s o c i a t e d w i t h g r a i n boundary p e n e t r a t i o n by l i q u i d copper.  I t i s therefore possible that at  l e a s t some o f K i n g e r y ' s samples e x p e r i e n c e d much l e s s  expansion  d u r i n g s i n t e r i n g than d i d t h o s e o f t h e p r e s e n t work.  However,  even i f h i s specimens d i d n o t e x h i b i t any Stage IV e x p a n s i o n , his i n t e r p r e t a t i o n of -his-dilatometric data i s s t i l l  invalid.  From t h e d i l a t o m e t r i c d a t a f o r Fe-Cu runs i n t h i s work, i t i s n o t p o s s i b l e t o i d e n t i f y t h e t i m e o r specimen dimensions  a t w h i c h Stage V ' s t a r t s ' .  Accordingly, the k i n e t i c s  162  o f Stage V s h r i n k a g e cannot be a n a l y s e d on t h e b a s i s o f l o g log p l o t s of the data.  However, m e t a l l o g r a p h i c and o t h e r  o b s e r v a t i o n s i n d i c a t e d t h a t ' s o l u t i o n due t o p r e s s u r e ' was the dominant p r o c e s s c a u s i n g s h r i n k a g e d u r i n g Stage IV and e a r l y Stage V.  T h e r e f o r e b o t h o f K i n g e r y ' s models f o r l i q u i d - p h a s e  s i n t e r i n g shrinkage  (rearrangement and ' s o l u t i o n due t o p r e s s u r e ' )  apply t o t h e s i n t e r i n g o f i r o n - c o p p e r compacts.  As demonstrated  above, however, K i n g e r y ' s c l a i m t h a t h i s own e x p e r i m e n t s w i t h Fe-Cu a r e i n s u p p o r t o f those t h e o r i e s , i s q u i t e u n j u s t i f i e d .  4.2  Comparison w i t h B o c k s t i e g e l ' s Work The o b s e r v a t i o n s i n t h i s work o f t h e e f f e c t o f  p a r t i c l e s i z e on Stage IV and Stage V b e h a v i o u r  are i n close  agreement w i t h t h o s e o f B o c k s t i e g e l [15] (see F i g u r e 8 ) . B o c k s t i e g e l d i d n o t o b s e r v e Stage I I I c o n t r a c t i o n i n any o f h i s experiments.  T h i s i s r e a d i l y e x p l a i n e d i f he h e a v i l y  p r e s i n t e r e d a l l h i s specimens p r i o r t o u s i n g them f o r d i l a tometry.  D e t a i l s o f h i s specimen p r e p a r a t i o n a r e n o t d e s c r i b e d  [1.5]; however, t h e Stage IV expansions s i m i l a r t o those observed  w h i c h he observed a r e  i n t h e p r e s e n t work f o r p r e s i n t e r e d  samples o f r o u g h l y comparable powder s i z e  (e.g. 3.04% (AL/Lo)  i n a 53 t o 6 3 t i powder Fe-20 Cu specimen, PCM-2-19) . m  compacts presumably expanded l e s s because o f lower l i q u i d c o n t e n t - (7.5% C u ) .  Bockstiegel* s  (copper)  163  Bockstiegel attributed  a l l t h e e x p a n s i o n i n Fe-Cu  compacts t o d i f f u s i o n o f copper i n t o i r o n . i n t h i s work t h a t a more i m p o r t a n t  I t has been shown  r o l e i s p l a y e d by t h e  l i q u i d penetration of g r a i n boundaries.  Bockstiegel also  proposed t h a t a s o l i d i r o n - r i c h s k e l e t o n e x i s t e d t h r o u g h o u t l i q u i d - p h a s e s i n t e r i n g , and t h a t s h r i n k a g e was by a s o l u t i o n r e p r e c i p i t a t i o n p r o c e s s ( d e s c r i b e d i n S e c t i o n 1.4.2). S e v e r a l problems a r e a s s o c i a t e d w i t h t h e mechanism proposed.  F i r s t , m e t a l l o g r a p h y has shown i n t h e p r e s e n t  work  t h a t t h e i r o n i s n o t i n t h e form o f a s o l i d s k e l e t o n t h r o u g h o u t much o f t h e s i n t e r i n g p r o c e s s .  Second, B o c k s t i e g e l s 1  theory  r e q u i r e s complete w e t t i n g , w h i c h was shown n o t t o e x i s t i n Stage V i n t h i s work.  late  T h i r d , t h e mechanism i n v o l v e s t h e  l o n g range t r a n s p o r t o f a c o n s i d e r a b l e mass o f i r o n i n a s h o r t time.  Y e t t h e r e i s no o b v i o u s d r i v i n g f o r c e f o r such t r a n s p o r t  o r f o r d i s s o l u t i o n and r e p r e c i p i t a t i o n .  4.3  Comparison w i t h Other P r e v i o u s Work The Heavy A l l o y Mechanism w h i c h was proposed by L e n e l  causes s m a l l i r o n p a r t i c l e s t o d i s s o l v e and r e p r e c i p i t a t e l a r g e r ones.  on  The mechanism was o b s e r v e d t o o p e r a t e i n i r o n -  copper i n t h e p r e s e n t work.  The p r o c e s s i s n o t c o n s i d e r e d t o  cause d e n s i f i c a t i o n s i n c e t h e removal o f s m a l l p a r t i c l e s and growth o f l a r g e ones does n o t n e c e s s a r i l y l e a d t o complete d e n s i f i c a t i o n without high l i q u i d contents  [18]. In f a c t ,  164  the mechanism can cause d e n s i f i c a t i o n o n l y i n compacts where the s m a l l p a r t i c l e s h o l d l a r g e r ones a p a r t .  I f the  small  p a r t i c l e s e x i s t a t i n t e r s t i t i a l s i t e s , between l a r g e r ones, no d e n s i f i c a t i o n would r e s u l t from t h e i r r e m o v a l . As i n t h i s work, o t h e r i n v e s t i g a t o r s [14,17,20,21] o b s e r v e d t h a t the f i n a l s i n t e r e d s t r u c t u r e o f Fe-Cu compacts (of  about 20% copper) were rounded i r o n - r i c h p a r t i c l e s i n  c o n t i n u o u s c o n t a c t , w i t h copper f i l l i n g t h e spaces of the network. proposed why  No p r e v i o u s  i n v e s t i g a t o r , however, has  such a s t r u c t u r e s h o u l d form f o l l o w i n g g r a i n  boundary p e n e t r a t i o n and/or rearrangement. cause i s c o n s i d e r e d  4.4  interstitial  In t h i s work the  t o be a changing d i h e d r a l a n g l e .  G r a i n Boundary P e n e t r a t i o n and t h e D i h e d r a l A n g l e B e r n e r et at.  [12] o b s e r v e d g r a i n boundary  penetra-  t i o n d u r i n g l i q u i d - p h a s e s i n t e r i n g and c o n c l u d e d t h a t i t was t h e cause o f e x p a n s i o n d u r i n g the l i q u i d - p h a s e s i n t e r i n g o f Fe-Cu m i x t u r e s .  They measured t h e d i h e d r a l a n g l e s o b s e r v e d  i n s e c t i o n s o f specimens w h i c h had been s i n t e r e d a t v a r i o u s temperatures.  According  to the technique  [7,9]  t h e most  f r e q u e n t l y o b s e r v e d v a l u e , cj)^, i s the t r u e v a l u e o f cj> f o r a system a t a g i v e n t e m p e r a t u r e . (see Figure- 70)  Thus a c c o r d i n g  cf> f o r the system a t 1180°C was  to t h e i r  data  21°.  I n the p r e s e n t work v i r t u a l l y a l l g r a i n b o u n d a r i e s were p e n e t r a t e d  by copper d u r i n g l i q u i d - p h a s e s i n t e r i n g .  That  165  0  10  20  30  i.0  50  60  70  DIHEDRAL ANGLE 6 [DEG]  F i g u r e 70.  80  166  means t h a t t h e d i h e d r a l a n g l e was z e r o d u r i n g Stages I I I and IV.  Because B e r n e r et at. [12] a l s o o b s e r v e d g r a i n  boundary-  p e n e t r a t i o n (and e x p l a i n e d e x p a n s i o n i n terms o f g r a i n boundary p e n e t r a t i o n ) , i t must be c o n c l u d e d t h a t t h e d i h e d r a l a n g l e was a l s o z e r o i n t h e i r system.totfet theirhmeasurements  o f a)  i n d i c a t e d t h a t i t was p o s i t i v e . Faced w i t h t h a t dilemma, they e x p l a i n e d t h e p e n e t r a t i o n o f g r a i n b o u n d a r i e s by c l a i m i n g t h a t t h e v a l u e o f a) v a r i e d (as low as z e r o ) , f o r d i f f e r e n t g r a i n b o u n d a r i e s a t t h e same temperature.  They based t h a t c l a i m on t h e f a c t t h a t t h e d i s -  t r i b u t i o n o f <J> (as measured i n t h e m i c r o s t r u c t u r e s ) , changed a s s y m e t r i c a l l y w i t h temperature  (see F i g u r e 7 0 ) .  In fact,  when t h e most f r e q u e n t l y o b s e r v e d a n g l e (tfV^) had a low v a l u e , t h e d i s t r i b u t i o n was l o g - n o r m a l , whereas t h e d i s t r i b u t i o n was normal when d) was l a r g e . m  That t h e d i s t r i b u t i o n s h o u l d  change i n such a manner i s e x a c t l y what one would when a) i s t h e t r u e d i h e d r a l a n g l e . o n l y ) d i h e d r a l a n g l e o f a system  expect,  I f d) i s t h e t r u e (and  (and measurements a r e made  o f t h e d i h e d r a l a n g l e s o b s e r v e d i n s e c t i o n s t a k e n a t random through a t h r e e - d i m e n s i o n a l m a t r i x ) , t h e n t h e lower i s <J>, the h i g h e r i s the frequency o f o b s e r v a t i o n o f angles l e s s t h a n <j) (= d> ) . m  Thus t h e e x p l a n a t i o n o f B e r n e r et al. [12] t h a t cf> was z e r o f o r some b o u n d a r i e s and n o t o t h e r s i s n o t s a t i s f a c t o r y . I t must t h e r e f o r e be c o n c l u d e d t h a t t h e i r method o f measurement o f d i h e d r a l a n g l e s was e r r o n e o u s .  167  B e r n e r et al. [12] o b s e r v e d t h a t p r e s i n t e r i n g o f i r o n powder compacts d e c r e a s e d t h e amount o f s w e l l i n g d u r i n g i n f i l t r a t i o n w i t h copper.  I n t h i s work a s i m i l a r o b s e r v a t i o n  was made o f t h e e f f e c t o f p r e s i n t e r i n g on t h e r a t e o f e x p a n s i o n ( i n Stage IV) o f Fe-22 Cu compacts.  This e f f e c t i s associated  w i t h a d e l a y i n t h e rearrangement p r o c e s s (due t o growth o f l a r g e r necks d u r i n g t h e p r e s i n t e r i n g t r e a t m e n t ) such t h a t t h e r e i s more p r o l o n g e d i n t e r f e r e n c e w i t h Stage I V e x p a n s i o n . The e f f e c t  o f a d d i t i o n s w h i c h reduce e x p a n s i o n i n  the Fe-Cu system ( i . e . C, Sn, Mn, P, W) [12] may>:be t o reduce t h e t o t a l amount o f oxygen i n t h e system, o r t h e amount w h i c h i s c o n c e n t r a t e d a t s o l i d - l i q u i d i n t e r f a c e s , b y a c t i n g as 'getters'.  That would i n c r e a s e t h e d i h e d r a l a n g l e and reduce  o r p r e v e n t g r a i n boundary p e n e t r a t i o n . (e.g. W) a r e n o t good oxygen  Some e x p a n s i o n i n h i b i t o r s  ' g e t t e r s ' , however.  suggested t h a t t h e y cause an i n c r e a s e i n y Y  s s  It is  o r decrease i n  , perhaps as a consequence o f s e g r e g a t i n g t o i n t e r f a c e s .  Chapter 5  CONCLUSION 5.1  Summary The d i m e n s i o n a l and d e n s i t y changes which o c c u r when  Fe-Cu powder compacts a r e s i n t e r e d above t h e m e l t i n g p o i n t o f copper can be i n t e r p r e t e d i n terms o f t h e o p e r a t i o n and i n t e r action of f i v e processes: a) b) c )  d)  e)  rearrangement solution  due t o p r e s s u r e  processes causing c o n t r a c t i on  coaIescence  penetration of s o l i d y-Fe g r a i n boundaries by- l i q u i d copper d i f f u s i o n o f up t o 9 w t % copper into s o l i d iron  processes causing e x p a n s i on  The s h r i n k a g e p r o c e s s e s a) t o c) o c c u r i n t h e sequence i n d i c a t e d b u t they o v e r l a p each o t h e r i n time t o a degree which i s determined by powder p a r t i c l e s i z e , t h e t h e r m a l h i s t o r y o f t h e compact and o t h e r parameters. 168  The two e x p a n s i o n  169  p r o c e s s e s d) and e) a l s o o c c u r t o g e t h e r , a l t h o u g h e x p a n s i o n due t o g r a i n boundary p e n e t r a t i o n t e r m i n a t e s e a r l i e r .  More-  over, the expansion processes operate simultaneously w i t h t h e f i r s t two o f t h e c o n t r a c t i o n p r o c e s s e s . give r i s e , t y p i c a l l y ,  These i n t e r a c t i o n s  t o a t h r e e - s t a g e sequence o f n e t dimen-  s i o n a l changes i n a compact d u r i n g l i q u i d - p h a s e s i n t e r i n g . The sequence i s : I)  Rapid  net shrinkage  II)  Rapid  and e x t e n s i v e n e t e x p a n s i o n  I II)  Net shrinkage a t a rate decreases with time  which  A s s o c i a t e d w i t h t h e s e dimensional°hehanges. i s t h e o c c u r r e n c e o f t h e f o l l o w i n g s t r u c t u r a l changes: a)  When c o p p e r m e l t s , s o l i d - s t a t e s i n t e r e d c o n t a c t s between i r o n p a r t i c l e s a r e e^liiiirh lima ibed bby a a c c o f n b iina t i u o n o c f d d l s s o I u t i o n o f i r o n i n c o p p e r and p e n e t r a t i o n o f g r a i n b o u n d a r i e s by l i q u i d .  b)  G r a i n b o u n d a r i e s i n then-i-ronr.r&ch ' s o I i d c o n t i n u e t o be p e n e t r a t e d by l i q u i d , and t h e s y s t e m c o n s i s t s o f s o l i d particles 'dispersed' in liquid, until the f i n a l shrinkage stage i s reached.  c)  During t h e f i n a l shrinkage stage a s o l i d s k e l e t o n i s r e - e s t a b l i s h e d and s h r i n k a g e o c c u r s by c o a l e s c e n c e o n l y .  When compacts a r e p r e s i n t e r e d f o r p r o l o n g e d p e r i o d s i n t h e s o l i d s t a t e (e.g. a t 1000°C), l a r g e r necks a r e e s t a b l i s h e d between i r o n p a r t i c l e s .  The complete d i s s o l u t i o n o f necks  a f t e r copper m e l t s i s thus d e l a y e d , and t h e r e i s e a r l i e r  170  i n t e r f e r e n c e between s h r i n k a g e by rearrangement and t h e expansion processes.  The r e s u l t i s a reduced n e t c o n t r a c t i o n i n  the e a r l y s t a g e o f l i q u i d - p h a s e s i n t e r i n g , and reduced n e t expansion  subsequently.  The i n i t i a l c o n t r a c t i o n s t a g e may  even become 'masked' e n t i r e l y . The  change from a ' d i s p e r s e d - s o l i d ' t o a c o a l e s c e d  s o l i d system i n t h e l a t e s t a g e s o f s i n t e r i n g i s a s s o c i a t e d w i t h a change i n t h e v a l u e o f Y energy.  S L  f  the s o l i d - l i q u i d  I t i s s u g g e s t e d t h a t YOT i s lowered  interfacial  by t h e p r e s e n c e  o f oxygen i n t h e compact, e s p e c i a l l y when t h e a v a i l a b l e oxygen has s e g r e g a t e d  to the s o l i d - l i q u i d i n t e r f a c e s during the period  i n w h i c h copper i s d i f f u s i n g i n t o i r o n .  The c o n t a c t and  d i h e d r a l a n g l e s i n t h e system a r e b o t h z e r o w h i l e t h i s c o n d i tion prevails.  G r a i n boundary p e n e t r a t i o n by l i q u i d copper i s  thus p o s s i b l e .  When t h e oxygen c o n c e n t r a t i o n i n t h e compact,  or the extent o f segregation a t s o l i d l i q u i d i n t e r f a c e s becomes r e d u c e d , a f t e r l o n g e r times o f s i n t e r i n g , Y  s l  increases  t o t h e e x t e n t t h a t both t h e c o n t a c t and d i h e d r a l a n g l e s become p o s i t i v e and c o a l e s c e n c e  o f s©ld!d p a r t i c l e s ensues.  This  e x p l a n a t i o n has n o t been advanced by any p r e v i o u s i n v e s t i g a t o r s o f l i q u i d phase s i n t e r i n g and may be c a p a b l e o f e x p l a i n i n g some r e p o r t e d o b s e r v a t i o n s f o r o t h e r systems b e s i d e s Fe-Cu. S m a l l a d d i t i o n s o f phosphorous and carbon a r e r e p o r t e d t o markedly reduce the;:amount o f e x p a n s i o n  which  o c c u r s when Fe-Cu powder compacts a r e l i q u i d - p h a s e s i n t e r e d .  171 T h i s can be e x p l a i n e d i f t h e a d d i t i o n s a c t as i n t e r n a l deo x i d a n t s i n t h e system. of  They may thus p r e v e n t t h e a t t a i n m e n t  a zero d i h e d r a l a n g l e and p r e v e n t t h e e x p a n s i o n which i s  o t h e r w i s e a s s o c i a t e d w i t h g r a i n boundary p e n e t r a t i o n . The e f f e c t , on t h e p r o g r e s s o f l i q u i d - p h a s e s i n t e r ing,  o f v a r i a b l e s such as powder p a r t i c l e s i z e , r a t e o f h e a t i n g  through t h e s m e l t i h g g t e m p e r a t u r e ,  i n i t i a l d e n s i t y o f com-  p a c t s , copper c o n t e n t o f t h e powder m i x t u r e and p r e a l l o y i n g of  t h e i r o n powder can be i n t e r p r e t e d i n terms o f t h e p r e d i c t -  a b l e e f f e c t s o f each v a r i a b l e on t h e s e v e r a l s h r i n k a g e and c o n t r a c t i o n p r o c e s s e s and t h e i r m u t u a l i n t e r a c t i o n s . The p r i n c i p a l c o n t r i b u t i o n s made, by t h i s work t o an u n d e r s t a n d i n g o f l i q u i d - p h a s e s i n t e r i n g , a r e as f o l l o w s : I )  D i mens i ona,bh§hanges a rehcfeheeBesai I (bf o f t h e o p e r a t i o n a n d i n t e r a c t i o n o f up to f i v e d i f f e r e n t p r o c e s s e s .  2)  While the dihedral angle i s zero, c o n d i t i o n s f o r r a p i d d e n s i f i c a t i o n by r e a r r a n g e m e n t and s o l u t i o n due t o pressure exist. However, a z e r o d i h e d r a l angle a l s o promotes s i m u l t a n e o u s e x p a n s i o n by t h e p e n e t r a t i o n of s o l i d g r a i n b o u n d a r i e s . Thus i n a " c o m p l e t e l y w e t t i n g " system ( i . e . 6 = 0) w i t h (J) = 0°, n e t s h r i n k a g e w i l l n o t n e c e s s a r i l y be o b s e r v e d i n a given sintering period.  . 3)  r  The c o n t a c t and d i h e d r a l a n g l e s i n some l i q u i d - p h a s e s i n t e r i n g s y s t e m s ( ' i n c l u d i n g F e - C u ) may c h a n g e f r o m zero to p o s i t i v e values during the c o u r s e o f s i n t e r i n g , as t h e r e s u l t o f a change i n t h e c o n c e n t r a t i o n o r d i s t r i b u t i o n o f an i m p u r i t y s p e c i e s i n t h e system. The e f f e c t i s a c h a n g e f r o m rapid shrinkage processes to the slower process of coalescence.  172 4)  5.2  Large changes i n l i q u i d - p h a s e s i n t e r ing b e h a v i o u r can r e s u l t from small changes i n c o m p a c t i n g and s i n t e r i n g p a r a m e t e r s , due t o t h e c o m p l e x i n t e r a c t i o n s o f t h e s e v e r a l s h r i n k a g e and expansion processes, which a r e a f f e c t e d by t h e same p a r a m e t e r s . That e x p l a i n s t h e marked d i f f e r e n c e i n behaviour reported f o ra given system by d i f f e r e n t p r e v i o u s i n v e s t i g a t o r s .  F u t u r e Work I t i s suggested t h a t f u t u r e work i n t h e Fe-Cu system  be d i r e c t e d towards an i n v e s t i g a t i o n o f t h e e f f e c t s o f " a d d i t i o n s " (e.g. W, Sn, P) on t h e v a l u e s o f 8 and <j>, t h e w e t t i n g and d i h e d r a l a n g l e s , o f t h e Fe-Cu system.  S e s s i l e drop e x p e r i -  ments, under c o n d i t i o n s o f a c o n t r o l l e d oxygen p o t e n t i a l , i n which s m a l l " a d d i t i o n s " a r e made t o t h e copper l i q u i d l e a d t o a b e t t e r u n d e r s t a n d i n g o f how oxygen and o t h e r effect Y « S L  The w e t t i n g  should additions  and d i h e d r a l a n g l e s may b o t h be  measured i n s e s s i l e drop e x p e r i m e n t s t o g i v e d i r e c t r e s u l t s for the e f f e c t of additions. A r e - a n a l y s i s o f e x i s t i n g l i t e r a t u r e on l i q u i d - p h a s e s i n t e r i n g , i n systems o t h e r t h a n Fe-Cu, w i t h a v i e w t o d e t e r m i n i n g whether oxygen p l a y s an i m p o r t a n t r o l e , may l e a d t o a b e t t e r understanding of the liquid-phase systems and may r e s o l v e a p p a r e n t l y  s i n t e r i n g o f those  contradictory  observations.  REFERENCES  [1]  Metals  [2]  S m i t h , C.S.  [3]  K i n g e r y , W.D. 3T,  [4]  Handbook, 1973 e d i t i o n , V o l . 8, p. 293, S o c i e t y f o r M e t a l s , M e t a l s P a r k , Ohio. Trans.  A.I.M.E., 1948, V o l . 175, pp. 15-51.  J. Appl.  Physics,,  1959,  G e s s i n g e r , G.H.,  H.F.  Metallurgy,  [5]  T a y l o r , J.W.  [6]  Eremenko, V.N.,  301-  Progress  F i s c h m e i s t e r and H.L. 1973,  V o l . 16, pp.  in Nuclear  Lukas.  119-127.  Engineering  Series  3  1959, S e r i e s 5, V o l . 2, pp. 398-416, Pergamon P r e s s , New York.  Liquid  Phase  Bureau, New  [7]  J . White.  [8]  S u n d q u i s t , B.E.  [9]  VanvV.Mc.'k, L.H.  Yu. V. N a i d i c h and I.A. Sintering  York.  1970,  3  S i n t e r i n g and  Related  81-108, Plenum P r e s s , New Acta. Trans.  Met.,  pp.  Lavrimenko.  19-21.  Phenomena,  York.  Consultants  1973,  pp.  1964, V o l . 12, pp. 67-86.  A.I.M.E., 1951, V o l . 3, pp. 251-259.  Whalen, J . and M. Humenik. Proc. 18th Annual Powder Metallurgy Technical Conference, 1962, pp. 85-98,  M e t a l Powder I n d u s t r i e s Fed., New  [11]  V o l . 3, pp.  i „ 306. Powder  [10]  American  Hough, R.R. and R. R o l l s . pp. 2471-76. 173  Metl  Trans.,  York.  1971, V o l . 2,  174 [12]  B e r n e r , D., H.E. Exner and G. Petzow. in  Powder  Metallurgy,  Modern  1974, V o l . 6, pp.  M e t a l Powder I n d u s t r i e s F e d . , P r i n c e t o n , Tripler.  N.J.  [13]  Inman, M.C. and H.R. 8, pp. 105-166.  [14]  K i n g e r y , W.D.  [15]  B o c k s t i e g e l , G.  1959, V o l . 79,  No.  [16]  P r i c e , G.H.S., C.J. S m i t h e l l s and S.V. W i l l i a m s . Met., 1938, V o l . 62, pp. 239-264.  J.  [17]  L e n e l , F.V.  [18]  K i n g e r y , W.D.  [19]  Warren, R.  [2.0]  N o r t h c o t t , L. and C.J. L e a d b e a t e r . Special Report No. 38, pp. 142^-50, I r o n and S t e e l I n s t . , London, 1947.  [21]  Chadwick, R., E.R. B r o a d f i e l d , and S.E. Pugh. Special Report No. 38, pp. 151-157, I r o n and S t e e l I n s t . London, 1947.  [2.2]  S i l b e r e i s e n , H. Powder Metallurgy, I n t e r s c i e n c e , New York.  [23]  D a u t z e n b e r g , N.  [24]  T r u d e l , Y. and R. A n g e r s .  [25]  L e n e l , F.V.  J. Appl. Stahl  Trans.  Physios, und  17, pp. 1187-1201.  Met. Revs.,  Developments  237-50,  1963, V o l .  1959, V o l . 3, pp. 307-10.  Essen,  Inst.  A.I.M.E., 1948, V o l . 175, pp. 878-95.  Ceramic  Fabrication  Processes,  131-143, J . W i l e y and Sons I n c . , New Y o r k .  1958,  pp.  J. Mat Sci., 1968, V o l . 3, pp. 471-85.  Archiv  f.d.  1961, pp. 611-27,  Eisenhuttenwesen,  1970,  V o l . 41, No. 10, pp. 1005-10. Procs.  1973  Int'l.  Powder  Metallurgy Conf., 1973, pp. 306-322, M e t a l Powder I n d u s t r i e s Fed. and Am. Powder M e t a l l u r g y I n s t . , P r i n c e t o n , N.J. The Physics  of Powder  Metallurgy,  pp. 238-53, McGraw H i l l Book Co., New York.  1951,  175  [26]  Ramakrishnan, of  Powder  P. and R. Lakshminarasimhan. Metallurgy  Journal  Int'l.  Journal  1967, V o l . 3, No. 2, pp. 63-68.  [27]  K r a n t z , T.  [28]  Matsumura, G.  [29]  Gumme.son,  [30]  O ' B r i e n , T.E. and A.C.D. C h a k l a d e r . J. Amer. Ceram. 1974, V o l . 57, No. 8, pp. 329-32.  [31]  C h a k l a d e r , A.C.D. M e t a l l u r g y Department, The U n i v e r s i t y of B r i t i s h Columbia, 1974, p r i v a t e communication.  Vol.  Int'l.  3  of Powder  5, No. 2, pp. 33-43. Planseeberiohte  1961, V o l . 9, pp. 33-35. P.U.  and L. F o r s s .  Pur  Proa.  Metallurgy,  1969,  Pulvermetallurgie,  11th Annual  Meeting,  1955, pp. 55-65, M e t a l Powder A s s o c i a t i o n , New York.  Soc,  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0078694/manifest

Comment

Related Items