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The deformation behaviour of fibre-reinforced copper. Howard, Graeme Claude 1964

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THE DEFORMATION BEHAVIOUR OF FIBRE-REINFORCED  COPPER  by  >GRAEME CLAUDE HOWARD  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER. OF APPLIED SCIENCE IN THE DEPARTMENT OF METALLURGY  We a c c e p t t h i s t h e s i s as  conforming t o  s t a n d a r d r e q u i r e d from c a n d i d a t e s the  degree  the for  of  MASTER OF APPLIED SCIENCE  Members o f the  Department of  Metallurgy  THE UNIVERSITY OF BRITISH COLUMBIA  March,  1964  In presenting  t h i s thesis i n p a r t i a l f u l f i l m e n t of  the requirements f o r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study.  I further agree that permission  f o r extensive copying of t h i s thesis f o r scholarly purposes may granted by the Head of my Department or by his  be  representatives..  It i s understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department .of  Metallurgy  The University of B r i t i s h Columbia, Vancouver. 8, Canada. Date  March  1964  •ABSTRACT  :  The d e f o r m a t i o n "behaviour o f copper, r e i n f o r c e d w i t h i r o n and  s t e e l f i b r e s has been i n v e s t i g a t e d .  Parameters  studied include:  fibre  diameter, - m a t r i x mean f r e e p a t h , and r e l a t i v e s t r e n g t h o f f i b r e and m a t r i x .  No s t r e n g t h e n i n g e f f e c t has.been observed which can.be a t t r i b u t e d to  f i b r e . s i z e alone.  However, i t i s suggested t h a t t h e s t r e n g t h of - metal  f i b r e - r e i n f o r c e d metal, composites  a r e g r e a t l y i n f l u e n c e d , by a . " s i z e . e f f e c t "  i n . the m a t r i x .  A m o d i f i c a t i o n o f t h e t h e o r y o f combined a c t i o n , has been proposed for  p r e d i c t i n g t h e s t r e n g t h o f a f i b r e - r e i n f o r c e d composite, v i z ;  ^~c  =  A  f  +  A  m  ^m  +  A  f  l  A  K  d  f "  l  /  2  .  where A i s volume f r a c t i o n , f r e f e r s t o f i b r e , m r e f e r s t o m a t r i x , d^. is. f i b r e diameter, and. K i s a c o n s t a n t whose. v a l u e depends on the-hardness  o f the f i b r e .  Weakening o f t h e m a t r i x - f i b r e i n t e r f a c e i n composites  o f copper  and s t e e l f i b r e s has been a t t r i b u t e d . t o s e g r e g a t i o n , o f carbon t o t h e interface. • A l l o y s c o n t a i n i n g 6 t o 8 weight p e r cent copper i n - i r o n have been shown.to e x h i b i t a . m a r t e n s i t i c t r a n s f o r m a t i o n when c o o l e d from t h e V r e g i o n o f the; Fe-Cu phase  diagram,..  iii. TABLE OF CONTENTS . • •Page I . INTRODUCTION  1  A. General.  1  B. P r e v i o u s Work C• ' S C ;  O p 6  •  %  • - •  I I . EXPERIMENTAL PROCEDURE  .2 •  •  •  * •  •  *  • •• • •  •  *. •  ... .•  11  A. M a t e r i a l s •B.-Composite P r e p a r a t i o n ... 1. Wire Composites 2. Powder Composites . . . . . ... . . . C. Swaging and Drawing D. Heat T r e a t i n g E . Measurement o f Fibre" C o n c e n t r a t i o n F. T e n s i l e T e s t i n g G. M e t a l l o g r a p h y . ......... .. . . . . I I I . RESULTS A. . Composites Made From H i g h Carbon S t e e l Wire 1. S t r u c t u r e s . ... . . . . .2. S i z e E f f e c t s . \ . . . 3. S t u d i e s o f Heterogeneous Y i e l d i n g . . a) E f f e c t o f C o l d Working b) P r o p e r t i e s o f S i n g l e S t e e l W i r e s c) E f f e c t o f I n t e r r u p t e d L o a d i n g d) E f f e c t o f S t r a i n A g e i n g e) O b s e r v a t i o n s D u r i n g L o a d i n g  .11  . . . . .  Bundles . . . . . . ......... ......  .  B. Composites Made From S i n t e r e d Armco I r o n Powder . ... 1. - S t r u c t u r e s . 2. S i z e E f f e c t s 3. Heterogeneous Y i e l d i n g k. Heat Treatments on S a t u r a t e d I r o n Powder  Composites . . . .......  1  12 .12 13 .16 16 18 18 18 19 19 "19 22 29 32 32 32 32 35 35 35 37 ^3  . .Uk  a) R e s u l t s w i t h -100 +150 mesh Powder Composites ... . . . . .. . . . . . . . . .... . b) R e s u l t s w i t h -325 mesh Powder. Composites . IV. DISCUSSION  ^  • •  kk 48 '57  A. S t r u c t u r e and A s p e c t R a t i o s o f Composites • 57'. B. Y i e l d B e h a v i o u r o f U n s a t u r a t e d Powder Composites . . 59 ''':. 1. Heterogeneous Y i e l d i n g 59 2. S i z e Dependence o f Y i e l d S t r e s s 60 C. Y i e l d Behaviour o f Wire Composites 61 1.. O r i g i n o f Two Y i e l d P o i n t s . . . 61 2. Heterogeneous Y i e l d i n g . . . . . . . . . . . . . 61 3. S i z e Dependence o f Y i e l d S t r e s s . . . . . . . . . 64 D. E f f e c t o f Heat Treatment on S a t u r a t e d Powder Composites 65 E. D e f o r m a t i o n Behaviour o f M e t a l F i b r e R e i n f o r c e d M e t a l s 73  • Table of Contents Continued... Page 79  V. CONCLUSIONS  ,' 80  VI. SUGGESTED FUTURE WORK VII'. BIBLIOGRAPHY  .  VIII. APPENDICES . .  '  ,81 83  V.  LIST OF FIGURES Figure 1.  '.". Page • Schematic R e l a t i o n Between F i b r e T e n s i l e S t r e s s (^T^) I n t e r f a c i a l -Shear' S t r e s s . ("f ) and F i b r e • Length .. .  2.  3.  • R e l a t i o n s h i p . Between C o m p o s i t e . T e n s i l e S t r e n g t h and Volume P e r C e n t ' F i b r e s f o r ' V a r i o u s F i b r e . L e n g t h s .  5.  - System, f o r I n f i l t r a t i o n o f S t e e l Wire. Bundles ;  Cross-section  (a) a n d L o n g i t u d i n a l ' S e c t i o n  .. ... . •.  7. •8.  . . . .  . E f f e c t o f A n n e a l i n g 1 hour a t 680°C, Specimen W-l-A-11 . D i s t r i b u t i o n o f F i b r e s i n t h e Copper M a t r i x ,  10.  11.  12.  13.  -14.  .14  .20 -21  Specimen  ••W-l-12 ..... ... . . ... . . . . . . . ... . ..... T y p i c a l S t r e s s - P l a s t i c ' S t r a i n Curves f o r V a r i o u s Specimen S i z e s (a).-Composite W-l-A, •• (b) Composite W-3-A . . . . . . . . . . Composite Y i e l d S t r e s s V e r s u s Specimen Diameter f o r Composites•W-l-A, W-2-A, and W-3-A.  .21  1  ;  9.  . .9  (b) o f  Specimen W-l-A-6 .6.  6  - T e n s i l e S t r e n g t h s o f Wires Drawn f r o m " S e v e r a l A l l o y s , " • Reproduced-.from R o b e r t s ~ . . . . . . . . . . . . . . . . . .  ...4.  5  Composite U l t i m a t e T e n s i l e S t r e s s . V e r s u s Specimen Diameter f o r Composites W-l-A,. W-2-A, and W-3-A  .  23 .24 25  .26  Method-of D e t e r m i n i n g Y P „ - and YP ., from , ,. „ matrix composite L o a d - E l o n g a t i o n Curves  27  M a t r i x Y i e l d - S t r e s s V e r s u s Specimen-Diameter f o r Composites W-l-A,.'W-2-A, and W-3-A  28  m o +  n  v  D i s t a n c e "D" ( F i g u r e 11) i n Per Cent E l o n g a t i o n V e r s u s Specimen Diameter f o r Composites W-l-A,' W-2-^A, and W-3-A . . . . ... ... ... ... ... ..... .....  . 30  D i s c o n t i n u o u s . Y i e l d E l o n g a t i o n as Measured From ^comx>osite Versus- Specimen Diameter f o r Composites W-l-A,: W-2^A, and-W-3-A  31  ;  15.  S t r e s s - P l a s t i c S t r a i n Curve F o r S i n g l e S t e e l Wire  . . .  .34  16.  D e f o r m a t i o n Bands on P o l i s h e d ' S u r f a c e o f Specimen W4L .  v.36  17.  S e c t i o n s Through"Iron Powder-Composites  18.  S t r e s s ' V e r s u s P l a s t i c S t r a i n f o r Selected-Specimen..  . ...........  •: S i z e s f o r -100 +150 mesh"Powder Composites ;  . . . .  .38  39,40  vi. List  o f Figures Continued..  Figure 19.  20.  21.  2 2 .  Page U l t i m a t e T e n s i l e S t r e s s V e r s u s Specimen Diameter f o r - 1 0 0 +I50 mesh Powder Composites . . . . . . . . . Composite Y i e l d - S t r e s s V e r s u s Specimen Diameter f o r - 1 0 0 +I50 mesh Powder Composites . . . . "'  k2  Photomicrograph o f - 1 0 0 " A i r c o o l e d " from 1  k^  + 1 5 0 0 2 0 ° C  mesh Powder Composite . .  ~.  S t r e s s - P l a s t i c S t r a i n Curves f o r V a r i o u s Heat Treatments on - 1 0 0  23.  kl  +I50 mesh Powder Composites  . . . . . . .  H-9  Photomicrograph o f - 3 2 5 mesh Powder Composite,-Quenched i n l i q u i d n i t r o g e n and aged f o r hour a t - 8 0 ° C .  5  1  2k.  Photomicrograph o f - 3 2 5 mesh Powder Composite,••Pack carburized at 9 2 0 ° C f o r minutes . . . . . . . . 1  0  0  5k  0  25.  S t r e s s - P l a s t i c S t r a i n Curves f o r V a r i o u s Heat Treatments on - 3 2 5 mesh Powder Composites . 5 5 .  26.  Y i e l d S t r e s s V e r s u s C o o l i n g Rate f o r " S a t u r a t e d " I r o n Powder Composites . . . .  5  6  Specimen Diameter V e r s u s P r e d i c t e d S t r e n g t h s o f t h e M a t r i x and F i b r e s  6  6  27.  2  8  .  29.  Proposed C o o l i n g - T r a n s f o r m a t i o n Diagram f o r I r o n - 7 $ > Copper A l l o y . .. . . . . . . . . . ... Assumed F i b r e D i s t r i b u t i o n  7 1 = :  7 5  vii. LIST OF TABLES Table I.  Page Swaging and Drawing Schedule  I I . •Work-Hardening Exponents III. IV.  S t r a i n Ageing Results Work-Hardening Exponents  ' .  16 32 35 kj>  • ACKNOWLEDGEMENT  The a u t h o r i s g r a t e f u l f o r t h e a d v i c e and encouragement g i v e n by his,research  d i r e c t o r y Dr. J . A . L u n d . • Thanks a r e a l s o extended t o ' ,  o t h e r f a c u l t y members and f e l l o w  graduate s t u d e n t s f o r many h e l p f u l  discussions. F i n a n c i a l assistance  in.the  form.of Defence Research Board Grants  No. 7 5 0 1 - 0 2 and No. 75OI-03 i s g r a t e f u l l y  acknowledged.  I.  A.  INTRODUCTION  . General The  advance of s c i e n c e and t e c h n o l o g y  depends t o a l a r g e degree  upon the development of improved s t r u c t u r a l components. . To t h i s end l a r g e amount o f time and  a  e f f o r t has been a l l o t t e d t o the c r e a t i o n and  i n v e s t i g a t i o n o f composite m a t e r i a l s which e x p l o i t the b e s t p r o p e r t i e s of different individual materials.  . The  greatest strengths  i n composite m a t e r i a l s a r e found i n  those which c o n t a i n a . l a r g e volume f r a c t i o n o f a d i s p e r s e d hard phase c o u p l e d w i t h a h i g h d e n s i t y o f d i s l o c a t i o n s i n the m a t r i x .  This  type  of m i c r o s t r u c t u r e can be produced i n s e v e r a l ways, i n c l u d i n g : p r e c i p i t a t i o n a t low temperatures from a s u p e r s a t u r a t e d d e c o m p o s i t i o n , . m e c h a n i c a l m i x i n g and and  solution, eutectoid  subsequent s i n t e r i n g o f powders,  internal' oxidation of s u i t a b l e a l l o y s .  •A study 'of the s t r e n g t h e n i n g of m i c r o s t r u c t u r e s would, be a c h i e v e d and  solid  has  mechanisms i n v o l v e d i n these  l e d t o the r e a l i z a t i o n t h a t the g r e a t e s t  strong  c o n s i d e r a t i o n s have been g i v e n  methods, of l o a d t r a n s f e r from:the d u c t i l e matrix, t o the h a r d e r phase. . The  strengths  i f the d i s p e r s e d hard phase p a r t i c l e s were v e r y  loaded t o f r a c t u r e C o n s e q u e n t l y ,  types  to  dispersed  r e s u l t o f such i n v e s t i g a t i o n s , has been the c o n c l u s i o n t h a t  g r e a t e r s t r e n g t h s would be  r e a l i z e d i f the d i s p e r s e d p a r t i c l e s were  needle shaped, thus accommodating maximum.load t r a n s f e r .  A c c o r d i n g l y , r e c e n t i n v e s t i g a t o r s have c o n s i d e r e d  combining  f i b r o u s m a t e r i a l s w i t h r e l a t i v e l y weak binder, m a t e r i a l s , thus u t i l i z i n g the f a c t t h a t f i b r e s or w i r e s  can be e x c e e d i n g l y  s t r o n g and  can e x h i b i t  -2  m e c h a n i c a l p r o p e r t i e s s u p e r i o r t o those they a r e d e r i v e d .  Several techniques  -  o f the b u l k m a t e r i a l from which  have been developed f o r i n c o r p o r a t i n g  s t r o n g f i b r e s i n r e l a t i v e l y weaker m a t r i c e s  and  a theory p r e d i c t i n g  composite s t r e n g t h s has been developed.  B.  P r e v i o u s Work; Much o f the r e s e a r c h a s s o c i a t e d w i t h t h e fundamentals o f  reinforcement has  has been i n the f i e l d  statistically  r e l a t e d - the  of individual f i b r e s .  of glass reinforced p l a s t i c s .  s t r e n g t h of bundles of f i b r e s t o the  fibre Coleman"'" strength  Coleman's i d e a l i z e d mathematical-., a n a l y s i s i n d i c a t e d  t h a t the average t e n s i l e s t r e n g t h o f the bundle would b e ; l e s s t h a n average s t r e n g t h o b t a i n e d  the  f o r the i n d i v i d u a l f i b r e s making up t h e b u n d l e .  2 • Paratt  has  s t u d i e d t h e e f f e c t s of d e f e c t s i n g l a s s f i b r e s ' and  v a r i a t i o n s i n l e n g t h t o diameter r a t i o s and  discontinuous  (aspect r a t i o s ) f o r b o t h f u l l  length  fibres.  A method o f p r e d i c t i n g composite s t r e n g t h termed "The Combined A c t i o n " has been developed by D i e t z  from h i s work on  Theory o f fibreglass  4,5,6,7 reinforced plastics.  V a r i o u s workers  i s a l s o a p p l i c a b l e t o m e t a l l i c and What f o l l o w s i n the p r e s e n t  have shown t h a t t h i s  theory  ceramic f i b r e s i n m e t a l l i c m a t r i c e s .  review i s a b r i e f d i s c u s s i o n o f the t h e o r y  p r e d i c t i n g composite s t r e n g t h s p l u s an o u t l i n e o f some e x p e r i m e n t a l  for  results  p e r t a i n i n g to m e t a l l i c systems. F o r a volume f r a c t i o n o f f i b r e s g r e a t e r t h a n a c e r t a i n c r i t i c a l value M" , c  (to be d i s c u s s e d l a t e r ) the b r e a k i n g i s given  by:  s t r e s s of a f i b r e  composite,  - 3 -  %  ^ f  =  where  A  =  •srj^  ^m  +  C  1  )  the!.fracture s t r e s s o f f i b r e s removed from ' the composite the s t r e s s supported, by the m a t r i x when the fibres fracture the volume f r a c t i o n s o f the f i b r e s and m a t r i x respectively.  = = •  AJ^AJJJ  f  g •McDanels e t a l .  have g e n e r a l i z e d e q u a t i o n (1) t o a l l o w f o r  >  the p r e d i c t i o n o f the s t r e s s i n a composite •ft  ^ c  ft  =  „  V  where the  F  A  a t any. v a l u e o f s t r a i n , i . e .  ft f  ....,(2)  +  ^J^'s r e p r e s e n t s t r e s s e s a t a p a r t i c u l a r v a l u e o f  s t r a i n , t a k e n from the s t r e s s - s t r a i n curves o f the i n d i v i d u a l of t h e composite,  i n t h e c o n d i t i o n i n which t h e y e x i s t  i n the  components composite.  McDanels e t a l . i n t h e i r work on t u n g s t e n - f i b r e - r e i n f o r c e d copper d e f i n e d f o u r stages o f t e n s i l e b e h a v i o u r and a p p l i e d e q u a t i o n (2) one  of'them.  The  composites t o each  f o u r s t a g e s were:  I.  E l a s t i c deformation of f i b r e ; e l a s t i c deformation of matrix,  II.  E l a s t i c deformation of f i b r e ; p l a s t i c deformation of matrix,  III. IV.  P l a s t i c . d e f o r m a t i o n o f f i b r e ; p l a s t i c d e f o r m a t i o n o f matrix,. F a i l u r e of the  composite.  R e t u r n i n g t o e q u a t i o n ( 1 ) , i t i s n e c e s s a r y to c o n s i d e r the o f low volume f r a c t i o n s o f f i b r e s . s m a l l , then f a i l u r e the composite  I f the volume p e r cent o f f i b r e s i s  o f the f i b r e s need not l e a d t o immediate f a i l u r e  s i n c e t h e m a t r i x may  effects  work-harden-sufficiently.  of  Expressing  : t h i s m a t h e m a t i c a l l y , e q u a t i o n (1) h o l d s o n l y i f the b r e a k i n g s t r e s s o f the composite  i s g r e a t e r than t h a t o f the m a t r i x , i . e .  - 3 -  %  =  f  A  where SJ~£  the \,f r a c t u r e s t r e s s , o f f i b r e s removed from the composite the s t r e s s supported, by the m a t r i x when the fibres fracture the volume f r a c t i o n s o f the f i b r e s and m a t r i x respectively.  = =  Af,^  (!)  Ai  +  = •  g McDanels e t a l .  have g e n e r a l i z e d e q u a t i o n (1) t o a l l o w f o r  the p r e d i c t i o n o f the s t r e s s i n a composite ^ c  =  V  where the  F  ^rj^'  s  A  f  +  TT  m  a t any v a l u e o f s t r a i n , i . e . ,(2)  ^  represent stresses at a p a r t i c u l a r value of  s t r a i n , taken from the s t r e s s - s t r a i n curves o f t h e i n d i v i d u a l components o f t h e composite,  i n the c o n d i t i o n i n which t h e y e x i s t  i n the  composite.  McDanels e t a l . i n t h e i r work on t u n g s t e n - f i b r e - r e i n f o r c e d copper  composites  d e f i n e d f o u r stages o f t e n s i l e b e h a v i o u r and a p p l i e d e q u a t i o n (2) t o each one  o f them.  The  f o u r stages were:  I.  E l a s t i c deformation of f i b r e ; e l a s t i c deformation of matrix,  II.  - E l a s t i c deformation of f i b r e ; p l a s t i c deformation of matrix,  III.  P l a s t i c . d e f o r m a t i o n of f i b r e ; p l a s t i c deformation of matrix,  IV.  F a i l u r e o f the  composite.  R e t u r n i n g t o e q u a t i o n (1), i t i s . n e c e s s a r y to c o n s i d e r the o f low; volume f r a c t i o n s o f f i b r e s .  I f the volume p e r cent o f f i b r e s i s  s m a l l , then f a i l u r e o f the f i b r e s need not- l e a d t o immediate f a i l u r e the composite  s i n c e t h e m a t r i x may  effects  work-harden s u f f i c i e n t l y .  of  Expressing  t h i s m a t h e m a t i c a l l y , e q u a t i o n (1) h o l d s o n l y i f the b r e a k i n g s t r e s s o f the composite  i s g r e a t e r than t h a t o f t h e m a t r i x , i . e .  - k  .where XTu  i s the u l t i m a t e t e n s i l e s t r e n g t h o f the  -  matrix.  6 Combining-equations  (1) and  (3)  c r i t i c a l volume p e r  cent  fibres.  ef  g i v e s r i s e t o a n ~ e x p r e s s i o n f o r the  •A  ( ^"u  "  )  9 Dow -the  has  done a d e t a i l e d study o f the r e l a t i o n s h i p s between  a p p l i e d load,. i n t e r f a c i a l shear s t r e s s e s , and  i n a f i l a m e n t - r e i n f o r c e d composite m e t a l . 1.  t h e s e q u a n t i t i e s i s shown in- F i g u r e alignment of. the  fibre, t e n s i l e  stresses  A schematic r e p r e s e n t a t i o n  Assuming-uniform p a c k i n g  f i b r e s and. e q u a l s t r a i n i n g i n / t h e f i b r e s and  t h e i r i n t e r f a c e , a . p l a u s i b l e d i s t r i b u t i o n o f shear and  of  and  m a t r i x at  t e n s i l e .stresses i s  15 as shewn i n F i g u r e  lb  . . From.this.model, i t becomes e v i d e n t  f i b r e length,. designated are t o be  achieved.  :  Dow  L , c  i s required  that a  i f maximum f i b r e t e n s i l e  stresses  r e p o r t s t h a t L .depends on the e l a s t i c and c  p r o p e r t i e s o f the f i b r e s and matrix'. . The mechanism by which a . f i b r e c o n t r i b u t e s  critical  shear  i t s strength to a  •k composite i s one  of shear .  Thus, f o r a g i v e n . p a i r  l e n g t h o f f i b r e t h a t i s bonded:to the. m a t r i x must be • a.shear s t r e s s t h a t i s e q u i v a l e n t E q u a t i n g the  of m a t e r i a l s , sufficient-to  t o t h e - t e n s i l e s t r e s s on-the  shear load- ©n t h e . i n t e r f a c e t o the  %y-  W f ^ f  .=  ^  f  L  c  r  support  fibre.  t e n s i l e load necessary  -'to cause f a i l u r e ; of .the f i b r e g i v e s the . s o - c a l l e d , c r i t i c a l a s p e c t '  the  ratio,  Schematic Relation Between Stress i ^ } ^  Interfacial  and  Length  Rbre  Fibre Tensile  Shear Stress {Z ),  (L)  - 6-  o  r  ''L  l  c  k  where d  f  (5)  ^ f  r  i s the d i a m e t e r o f . t h e f i b r e , and T  i s the shear  s t r e s s a t the i n t e r f a c e .  Equation  (1) p r e d i c t s a l i n e a r r e l a t i o n s h i p between s t r e n g t h  and volume f r a c t i o n o f f i b r e s . predicted load o n l y - i f L ^  The f i b r e s however, w i l l  .L « •  F  o  c a r r y the f u l l  s h o r t e r f i b r e s t h e p r o p o r t i o n of  r  c  the l o a d c a r r i e d by the f i b r e s w i l l he l e s s and t h e r e s u l t s w i l l be a weaker composite.  T h i s concept i s shown s c h e m a t i c a l l y i n F i g u r e  v o l u m e percent  2.  fibres,of constant  diameter ( d ) f  F i g u r e 2.  Relationship.Between Composite T e n s i l e S t r e n g t h and Volume Per'Cent F i b r e s f o r V a r i o u s F i b r e L e n g t h s .  F i g u r e 2 , however,  i s o v e r - s i m p l i f i e d . s i n c e the  a s p e c t r a t i o may. be c o m p l i c a t e d by v a r i a t i o n s ..The bond at the f i b r e - m a t r i x relative  interface  in interfibre  restrains  from. the  interface  :  is increased.  p o s s i b i l i t y , t h a t . t h e aspect r a t i o  spacing  movement of" the  t o the f i b r e but the e f f e c t of t h i s r e s t r a i n t  the d i s t a n c e  critical  Thus,, t h e r e e x i s t s  h i g h volume percentages o f f i b r e and w i l l become h i g h e r  low.fibre  contents.  A l o n g t h e s e l i n e s , , Koppenaal and" Parikh" "^ s t a t e t h a t 1  silver-infiltrated, felts strengthening for slip,  i n some r e s p e c t s ,  i n p o l y c r y s t a l l i n e metals.  increasing.fibre  d e n s i t y the a v a i l a b l e  hardening accordingly increases since l a r g e r new d i s l o c a t i o n s  i n t o each p i l e - u p .  their  obstacles  interfaces.  -With larger  The r a t e o f work-  s t r e s s e s are  required to  force  . P a r i k h , u s i n g the H a l l - P e t c h . type  of r e l a t i o n s h i p :  -j/2 ^  and a s s o c i a t i n g  as  s l i p . l e n g t h d e c r e a s e s and a  number o f d i s l o c a t i o n s p i l e up f o r a g i v e n s t r a i n .  at  t o g r a i n boundary  The f i b r e s a c t  and d i s l o c a t i o n s p i l e up at the m a t r i x - f i b r e  the  the  i n the m i c r o s t r a i n i n g r e g i o n o f  i s analogous  as  w i l l be  lowered at  s t r e n g t h e n i n g mechanism p r e v a l e n t  .  matrix  i s reduced  f o r a g i v e n f i b r e diameter  8  y  =  + ,K d "  .(6)  d w i t h the average d i s t a n c e  the f i b r e - i n d e p e n d e n t p o r t i o n o f ^J*  between f i b r e s and ST  Q  , has shown t h a t v a r y i n g the  with available  y s l i p l e n g t h by changing, the f i b r e d e n s i t y ; i s q u i t e analogous t o the g r a i n s i z e  i n p o l y c r y s t a l l i n e metals.  was e s t a b l i s h e d e x p e r i m e n t a l l y f o r the  • The v a l i d i t y o f e q u a t i o n (6)  0.2%. y i e l d s t r q n g t h i n s i l v e r -  i n f i l t r a t e d , f e l t s , o f m i l d s t e e l , . molybdenum, t u n g s t e n and stainless  steel, f i b r e s .  changing  martensitic  ;  - 8 -  The r e s u l t s o f v a r i o u s workers a r e somewhat c o n t r a d i c t o r y on the e f f e c t o f w i r e d i a m e t e r i n r e i n f o r c i n g m e t a l l i c systems. J e c h et-.al found a s i z e e f f e c t i n t u n g s t e n - f i b r e - r e i n f o r c e d copper.  Their results  showed t h a t t h e composites c o n t a i n i n g f i n e r w i r e s had h i g h e r s t r e n g t h s  7 f o r a g i v e n volume f r a c t i o n of t h e components.  Cratchley  found, t h a t  0.002 i n . diameter f i b r e s gave s t r o n g e r composites than 0.005 i n . diameter f i b r e s but a t t r i b u t e d t h i s s t r e n g t h i n c r e a s e t o d i f f e r e n c e s i n w i r e drawing c o n d i t i o n s .  The l o a d t r a n s f e r , f o r a g i v e n a s p e c t r a t i o ,  actually slightly less efficient  f o r the t h i n n e r f i b r e s but t h i s  was was  a t t r i b u t e d t o e f f e c t s due t o o r i e n t a t i o n . . Of the s e v e r a l methods used t o produce  fibre-reinforced  composites,  k 11  the i n f i l t r a t i o n t e c h n i q u e has been used most w i d e l y . .Sutton '  has  used vacuum i n f i l t r a t i o n t o i n c o r p o r a t e alumina whiskers i n s i l v e r aluminum.  Jech  5  et a l  and K e l l y  6  and  have used i n f i l t r a t i o n t e c h n i q u e s i n  t h e i r i n v e s t i g a t i o n s o f the t u n g s t e n w i r e - c o p p e r m a t r i x system.  Koppenaal  10 and P a r i k h  a l s o c o n c e n t r a t e d on i n f i l t r a t i o n as a means o f p r o d u c i n g  metal-wire f e l t s w i t h a s i l v e r m a t r i x . Some o t h e r t e c h n i q u e s which have been s u c c e s s f u l l y employed t o produce f i b r e - r e i n f o r c e d systems  i n c l u d e : (a) the compacting  and  s i n t e r i n g . o f m e t a l l i c powders around m e t a l l i c and n o n - m e t a l l i c f i b r e s  7,12  ;  (b) the p r o d u c t i o n o f f i b r e s o f an i n t e r m e t a l l i c i n s i t u i n the m a t r i x m e t a l by s u i t a b l e s o l i d i f i c a t i o n  6  13 or heat treatment ^; and  (c) the working  i n t o wire o f c e r t a i n c o p p e r - i r o n a l l o y s i n which an excess o f i r o n over the s o l i d s o l u b i l i t y l i m i t i n copper i s p r e s e n t as i r o n d e n d r i t e s i n the o r i g i n a l cast  alloy  lk  - 9 -  C.  Scope For the purpose of the p r e s e n t  i n v e s t i g a t i o n i t was  t h a t use might be made o f the f a c t t h a t the t e n s i l e drawn from many m e t a l l i c elements, diameter  (Figure  increase  strength  with decreasing  felt of wires  wire  3).  »  F i g u r e 3»  2  t  4 DIAMETER. MILS  I  10  T e n s i l e S t r e n g t h s of Wires Drawn From S e v e r a l Alloys. Reproduced from Roberts-*-".  - 10 -  Thus, i f s t e e l o r i r o n w i r e s c o u l d be i n c o r p o r a t e d i n t o a d u c t i l e m a t r i x and the r e s u l t i n g  composite  swaged and drawn t o s m a l l  s i z e s , a study c o u l d be. made o f t h e s t r e n g t h e n i n g e f f e c t diameter  (whisker s i z e and below) p o l y c r y s t a l l i n e  o f a system would a l l o w v a r i a t i o n s  wires.  of very small Proper c h o i c e  t o be o b t a i n e d i n t h e r e l a t i v e  p r o p e r t i e s o f t h e m a t r i x and t h e f i b r e s by s u i t a b l e , heat  treatments.  In t h i s way a study o f the d e f o r m a t i o n b e h a v i o u r o f f i b r e s and m a t r i c e s o f v a r y i n g r e l a t i v e s t r e n g t h s c o u l d be made.  . Two p o s s i b l e methods, o f p r o d u c i n g the d e s i r e d type o f m i c r o s t r u c t u r e were  (a)  visualized:  I n f i l t r a t i o n o f a bundle  of i r o n o r s t e e l wires with  copper f o l l o w e d by swaging and drawing' o f t h e r e s u l t i n g (b) molten in  I n f i l t r a t i o n o f porous,  composite, and  s i n t e r e d , i r o n powder compacts w i t h  copper f o l l o w e d by swaging and drawing t o produce  copper.  molten  fibrous  iron  -  II.  A.  1  . -  EXPERIMENTAL PROCEDURE  Materials  '  The h i g h carbon s t e e l w i r e used i n t h i s p r o j e c t P r e c i s i o n Steel-Warehouse,"spring.grade"  1  Inc.,  and was 0 . 0 1 2  as r e c e i v e d , ' w a s  (Downers. Grove,  inches i n - d i a m e t e r .  1  1  1  .  )  .  was s u p p l i e d . b y -The w i r e was. o f  The c h e m i c a l  analysis,  as f o l l o w s :  Carbon  0 . 8 6 <fo  •Manganese  O.kk^o.  -Silicon  0 , 2 0 - f  Sulphur  0  .  0  1  0  5  %  Armco i r o n powder, h a v i n g n e a r l y p e r f e c t l y  spherical  particles  was s u p p l i e d by the F e d e r a l - M o g u l , Power P l a n t D i v i s i o n . , of Ann A r b o r , - M i c h . .The nominal c o m p o s i t i o n of the powder was: .: I r o n  9 9 . 9k <f m i n . 0  Carbon  0 . 0 1 2  Manganese  0  Phosphorus  0  Silicon  a minus 3 2 5  1  7  '  .  0  2  5  Trace  Two screened (a)  0  0 . . 0 0 5  Sulphur  t h i s work;  .  $  fractions  a ..minus 1 0 0  mesh f r a c t i o n  %  %  1°  max.  only.  of the a s - r e c e i v e d  mesh ( T y l e r )  plus: 1 5 0  of average p a r t i c l e  • The m a t r i x m e t a l f o r a l l composites copper,  analyzing  9  9  '  9  2  %  powder were used i n  mesh f r a c t i o n ,  size 2 5  ;  and  (b)  microns.  was " E l e c t r o l y t e  copper w i t h a nominal, oxygen c o n t e n t of  Tough P i t c h " Q.Ok°jo.  - 12 -  An e q u i l i b r i u m diagram Appendix  I.  T h i s system was  f o r t h e Fe-Cu system i s g i v e n i n  chosen f o r s e v e r a l r e a s o n s .  I t was  f e l t t h a t i r o n - c o p p e r composites would respond w e l l t o t h e r e q u i r e d swaging and drawing o p e r a t i o n s , w i t h the copper a c t i n g as a n a t u r a l " l u b r i c a n t " f o r d e f o r m a t i o n o f the i r o n and s t e e l .  Furthermore, t h e  system, a f t e r s a t u r a t i o n o f t h e i r o n w i t h copper, would be heat t r e a t a b l e and t h u s the r e l a t i v e varied.  s t r e n g t h s o f t h e m a t r i x and f i b r e c o u l d be  readily  The s o l u b i l i t y o f each component i n t h e o t h e r i s l i m i t e d  and  18,19 well defined  and no i n t e r m e t a l l i c compounds a r e p r e s e n t i n the  20 system  which might d e t r a c t from a sharp m a t r i x - f i b r e i n t e r f a c e .  a d d i t i o n , i t was  a p p r e c i a t e d t h a t the system s a t i s f i e s t h e b a s i c  necessary f o r i n f i l t r a t i o n  i n that  copper a r e s u b s t a n t i a l l y d i f f e r e n t  In conditions  (a) m e l t i n g p o i n t s o f pure i r o n and (1,527* C and 1,083°'C r e s p e c t i v e l y ) , !  (b) no phases o f h i g h e r m e l t i n g p o i n t e x i s t which might o b s t r u c t the c o n t i n u i t y o f ^ . i n f i l t r a t i o n , and (c) i r o n i s known t o be wetted  readily  21" by l i q u i d  copper  B. Composite 1.  Preparation  Wire  Composites  Bundles o f 0.012  i n c h d i a m e t e r h i g h carbon s t e e l w i r e were  : i . i n f i l t r a t e d w i t h copper u s i n g the f o l l o w i n g p r o c e d u r e s : (a) W i  r e s  of  a p p r o x i m a t e l y 9 i n c h e s i n l e n g t h were c l e a n e d i n an  aqueous s o l u t i o n c o n t a i n i n g U0 g . p . l . N a C 0 , 13 2  N a P 0 . 1 2 H 0 , 13 2  4  2  3  g.p.l..NaOH, 13  g . p . l . NaCN, and 6 g . p . l . N a S i 0 2  3  g.p.l.  a t about 80°C.  (b) One-hundred and twenty w i r e s were p l a c e d i n s i d e a.copper tube measuring  8 i n c h e s l o n g by 0.250 i n c h e s o u t s i d e d i a m e t e r .  The  wall  - 13 -  t h i c k n e s s o f the t u b i n g used was 0.040 i n c h e s . (c) The r e s u l t i n g assembly was drawn.through a 0 . 2 0 0 i n c h d i a m e t e r hardened s t e e l d i e t o i n c r e a s e t h e c l o s e n e s s o f p a c k i n g and. t o a i d i n the alignment o f t h e w i r e s p r i o r t o i n f i l t r a t i o n . (d) I n f i l t r a t i o n was c a r r i e d out i n a c l o s e d - e n d , f u s e d q u a r t z tube of i n s i d e d i a m e t e r s l i g h t l y g r e a t e r t h a n t h e drawn s t e e l w i r e - c o p p e r tube assembly. -The f u s e d q u a r t z tube was so p l a c e d i n a G l o - B a r f u r n a c e t h a t a l l but the t o p one i n c h of the copper tube melted.  The geometry o f the  system i s as shown i n F i g u r e k.  All  i n f i l t r a t i o n s were performed a t 1150°C . f o r 9 minutes under  fore-pump vacuum f o l l o w e d by 1 minute under a s l i g h t p o s i t i v e p r e s s u r e o f argon.  (The argon treatment was found n e c e s s a r y t o e l i m i n a t e  the o u t s i d e l a y e r o f copper.)  blistering  C o o l i n g t o room temperature was done under  a p o s i t i v e p r e s s u r e o f argon.  The r e s u l t i n g composite was e s s e n t i a l l y f r e e o f v o i d s .  The p a r t  o f t h e copper tube which d i d n o t melt kept t h e w i r e s t o g e t h e r and i n the c e n t e r o f t h e f u s e d q u a r t z tube d u r i n g . t h e time the r e m a i n i n g cdpper was i n t h e molten s t a t e .  The r e l a t i v e l y t h i c k c o a t i n g o f copper-which r e s u l t e d  on t h e o u t s i d e s u r f a c e o f the composite was d e s i r a b l e from.the p o i n t o f view o f subsequent r e d u c t i o n by wire-drawing.  2. Powder Composites Compacts o f -100 +150 mesh Armco i r o n powder were w i t h copper u s i n g the f o l l o w i n g p r o c e d u r e :  infiltrated  -.Ik -  ^.quortz tube  o  y  o  copper tube  steel wo res  o || s '  I  s I  i>  I  o O  Figure 4  o  I!  s  ^  molten copper  I B  !;  o  furnace  O  System For Infiltration of Steel Wwre Bundles  elements  - 15 (a)  Powders were p r e s s e d h y d r o s t a t i c a l l y i n bags made f r o m Gooch  t u b i n g , a t a p r e s s u r e o f a p p r o x i m a t e l y 25,000 (b) S i n t e r i n g of g r e e n compacts was  p.s.i.  e f f e c t e d i n 10 minutes a t  1150°C under d r y hydrogen. (e)  I n f i l t r a t i o n f o r 10 .minutes a t II10°C'. was c a r r i e d out-under  fore-pump,, vacuum i n a V i t r e o s i l  t u b e , p r o v i d i n g an e x c e s s o f copper  o v e r t h a t needed t o f i l l t h e v o i d s i n t h e i r o n s k e l e t o n .  The t e c h n i q u e ,  used was d e v e l o p e d by K r a n t z ' ^ . . T h i s p r o c e d u r e y i e l d e d composites 3 t o k i n c h e s l o n g by 0.460 i n c h e s i n diameter w i t h the f o l l o w i n g  characteristics:  - d e n s i t y o f s i n t e r e d i r o n s k e l e t o n 7^.0  ± 2% o f t h e o r e t i c a l  - d e n s i t y o f i n f i l t r a t e d compact 96.7 * 1% °f t h e o r e t i c a l . The c o m p o s i t e s were a n n e a l e d f o r one hour a t 680°C under d r y hydrogen t o ensure t h a t the:,matrix was n o t s u p e r s a t u r a t e d i n i r o n ; i . e . t h a t t h e m a t r i x was as d u c t i l e as p o s s i b l e f o r subsequent f o r m i n g o p e r a t i o n s . The p r o c e d u r e used f o r t h e -325 mesh Armco i r o n powder was e s s e n t i a l l y i d e n t i c a l t o t h a t d e s c r i b e d above e x c e p t t h a t no p r e s s u r e was used t o p r e p a r e g r e e n "compacts".  -A tube o f t h e l o o s e powder was  s i m p l y v i b r a t e d by t a p p i n g u n t i l no f u r t h e r change i n volume was and t h e r e s u l t i n g mass s i n t e r e d a t 1150°C.  observed  S i n t e r i n g i n t h i s case  was  done i n a fore-pump vacuum.  The c o m p o s i t e s p r o d u c e d f r o m -325 mesh powder had t h e f o l l o w i n g characteristics: - d e n s i t y o f s i n t e r e d i r o n s k e l e t o n 57•3% o f t h e o r e t i c a l - d e n s i t y o f i n f i l t r a t e d compact 96.5% o f t h e o r e t i c a l .  - 16 C.  -Swaging and Drawing The r e d u c t i o n i n s i z e o f t h e wire and powder composites was  c a r r i e d out u s i n g t h e schedule shown i n T a b l e I .  - TABLE;I. Swaging and Drawing' Schedule  Operation  • Annealing "... Treatment* *  Original Diameter (in.)  Final Diameter (in.)  o.46c*  •ft 0.270  Swaging  1 h r . a t 680°C  0.163  Swaging  1 h r . a t 680°C  0.126  Drawing Drawing Drawing Drawing Drawing Drawing Drawing Drawing  1 1 1 1 1 1 1 1  0.270  (powder)  O.25O ( w i r e s ) 0.163 0.126 O.O98  0.046  O.035 0.028 0.021  O.O35 0.028  D.  O.O77 0.046  0.060  ftft  O.O98  0.060  O.O77  ft  1  :  hr.; a t nr." a t hr. at hr. at hr. at hr..at hr. at hr. at  680°C 680°C 680°C 680°C 680°C 680°C 680°C 680°C  Powder composites o n l y . A l l a n n e a l i n g t r e a t m e n t s were c a r r i e d out i n a f l o w o f d r y hydrogen.  Heat T r e a t i n g Heat t r e a t m e n t s were c a r r i e d out on samples produced from i r o n  •powder composites i n which t h e i r o n component v, • had been c o m p l e t e l y  saturated  w i t h copper a t 1020°C. -Six p i e c e s o f composite, each 3 i n c h e s l o n g , were p l a c e d i n a ceramic b o a t .  S m a l l a l u m i n a spacers were placed-.at each end  t o ensure t h a t t h e w i r e s were n o t i n c o n t a c t . i n a .small tube f u r n a c e under d r y hydrogen gas.  Treatment was c a r r i e d out H e a t i n g f o r 15 h o u r s ' a t  1020°C t o ensure a l l o y e q u i l i b r i u m was f o l l o w e d b y c o o l i n g a t v a r i o u s  rates.  The term " a i r c o o l e d " w i l l be a p p l i e d t o d e s c r i b e t h e r a t e o f c o o l i n g which p r e v a i l e d - w h e n t h e boat was withdrawn from-the hot zone a t a p p r o x i m a t e l y  - 17  -  3 i n c h e s p e r second t o a p o i n t 12 i n c h e s d i s t a n t where the temperature was below 200°C.  The a c t u a l r a t e o f c o o l i n g i s e s t i m a t e d . t o be  t o l80°C./second. • C o o l i n g by t h i s method was  120  entirely effected i n  d r y hydrogen.  S e v e r a l specimens were quenched s o l u t i o n t r e a t m e n t temperature  (1020°C)."  i n l i q u i d , n i t r o g e n from the Specimens which had p r e v i o u s l y  been s o l u t i o n t r e a t e d and " a i r c o o l e d " were, i n t h i s c a s e , r e h e a t e d t o 1020°C f o r 20 minutes i n a v e r t i c a l tube f u r n a c e under a f l o w o f d r y hydrogen gas.  The s u s p e n s i o n was  t o drop i n t o a dewar o f l i q u i d  then c u t , a l l o w i n g . t h e  specimens  nitrogen.  • A f t e r s o l u t i o n treatment a t 1020°C as before,, one group o f specimens was  c a r b u r i z e d u s i n g a commercial pack c a r b u r i z i n g compound.  C a r b u r i z a t i o n f o r v a r i o u s times was at b o t h ends t o the atmosphere.  c a r r i e d out i n a. tube f u r n a c e open  The pack c a r b u r i z i n g compound  was  p l a c e d around, the specimens  i n a ceramic boat and the. f u r n a c e brought  t o a. temperature o f 920°C.  Homogenization was  a t 1020°C f o l l o w e d by  c a r r i e d out f o r 2 hours  "aircooling".  I n a d d i t i o n t o the heat t r e a t m e n t s mentioned above  several  o t h e r a n n e a l i n g and c o o l i n g p r o c e d u r e s were c a r r i e d out on c e r t a i n specimens.  A l l such t r e a t m e n t s were done i n a s m a l l tube f u r n a c e  under d r y hydrogen.  The a c t u a l procedure used f o r each specimen a l o n g  w i t h t h e p e r t i n e n t r e s u l t s w i l l be g i v e n i n " E x p e r i m e n t a l R e s u l t s " .  - 18 -  -E.  Measurement o f F i b r e C o n c e n t r a t i o n The volume percentage o f f i b r e s p r e s e n t i n t h e s t e e l w i r e -  copper m a t r i x composites was- c a l c u l a t e d from c r o s s - s e c t i o n m i c r o graphs u s i n g a random l i n e t e c h n i q u e .  The l e n g t h o f l i n e o c c u p i e d by  one phase was r e l a t e d t o t h e t o t a l l e n g t h o f t h e l i n e and averaged out over 12 random . l i n e s .  The volume percentage o f f i b r e s p r e s e n t i n t h e composites made from i r o n powders was-, r e a s o n a b l y assumed t o be e q u a l t o t h e d e n s i t y o f i r o n i n t h e a s - s i n t e r e d composites, s i n c e no d e t e c t a b l e growth o r s h r i n k a g e o f t h e i r o n compacts accompanied  F. •• T e n s i l e  iinfiltration:-....  Testing  A l l t e s t s were c a r r i e d o u t a t room temperature  on an I n s t r o n  T e n s i l e T e s t i n g machine u s i n g e i t h e r wedge type g r i p s o r f r i c t i o n  grips  22 p l u s s p e c i a l u n i v e r s a l mountings was  0.01  i n c h / minute  .  The c r o s s - h e a d speed i n a l l t e s t s  r e s u l t i n g i n s t r a i n rates of  O.OO67  min  - 1  for a l l  the s t e e l - w i r e composites and 0.01 m i n " f o r t h e composites made from 1  i r o n powder.  P e r c e n t e l o n g a t i o n s r e p o r t e d a r e based on c r o s s - h e a d  motion and thus a r e r e l a t i v e v a l u e s , r a t h e r t h a n a b s o l u t e l y a c c u r a t e . G-. - M e t a l l o g r a p h y An a l t e r n a t i n g p o l i s h - e t c h t e c h n i q u e was found n e c e s s a r y t o e l i m i n a t e smearing o f copper over t h e s u r f a c e s o f m e t a l l o g r a p h i c specimens. Specimens t o be viewed were mounted, i n " b a k e l i t e " and p o l i s h e d on f i v e emery p a p e r s . i n kerosene.  The mounts were then l a p p e d w i t h 1 m i c r o n diamond powder Each l a p p i n g s t e p was f o l l o w e d by e t c h i n g w i t h k^> p i c r i c  a c i d i n e t h a n o l f o r 15 seconds. the d e s i r e d  1  polish.  Four o r f i v e c y c l e s were r e q u i r e d t o g i v e  -.19  -  I I I . • RESULTS  A.  Composites . 1.  Made from.High Carbon S t e e l  Wire-Bundles  •Structures O b t a i n i n g f i b r e composites  o f the d e s i r e d s t r u c t u r e  by'infiltrating  s t e e l w i r e bundles w i t h l i q u i d copper proved t o be o n l y p a r t i a l l y •A r e d u c t i o n o f t h e composite d i a m e t e r t o a f i n a l specimen  successful.  s i z e o f 0.022 i n c h e s  ( c o r r e s p o n d i n g t o i n d i v i d u a l s t e e l w i r e diameters o f 0.0023) was the maximum obtainable.  Attempts  t o draw b e l o w . t h i s dimension l e d t o c r a c k i n g i n t h e  copper c o a t i n g or random ''necking" of. t h e composite.  I t was o r i g i n a l l y  felt  t h a t t h i s problem was a s s o c i a t e d w i t h i m p e r f e c t alignment of the s t e e l w i r e s in. the w i r e composites. difficulties  However, i n l a t e r work w i t h powder  composites  were e x p e r i e n c e d i n the same s i z e range, and i t became  apparent  .that t h e drawing d i e s a v a i l a b l e were n e c e s s i t a t i n g an u n u s u a l l y l a r g e r e d u c t i o n i n one pass a t t h e c r i t i c a l dimension.  M e c h a n i c a l p r o p e r t i e s and s t r u c t u r e s of t h e w i r e composites were examined over t h e range o f s i z e s which c o u l d be f a b r i c a t e d . . T e n s i l e was done on composite  specimens  testing  of 0.100 i n c h e s diameter ( i n d i v i d u a l wire  diameter a p p r o x i m a t e l y 0.00k i n c h e s ) and s m a l l e r .  Micrographs o f a c r o s s -  s e c t i o n and a l o n g i t u d i n a l s e c t i o n o f a t y p i c a l specimen are.shown i n Figure 5.  The r e l a t i v e l y sharp m a t r i x - f i b r e i n t e r f a c e and the e f f e c t o f  a n n e a l i n g a t 680°C are. shown i n F i g u r e 6.  As expected, the a n n e a l i n g  treatment s p h e r o i d i z e d the c a r b i d e i n t h e s t e e l w i r e s .  , . The volume percentage e f f i b r e s p r e s e n t i n these composites measured.using.the the  range  method o u t l i n e d ' i n 'the E x p e r i m e n t a l Procedure.  o f specimen  Over  diameters i n v e s t i g a t e d t h e volume p e r cent f i b r e s  was  F i g u r e 5.  C r o s s - s e c t i o n (a) and L o n g i t u d i n a l S e c t i o n (b) o f Specimen W - l - A - 6 , approximate w i r e d i a m e t e r 0 . 0 0 3 3 i n c h e s , annealed 1 hour a t 680°C, 2$ n i t a l e t c h , (a) X 2 0 0 (b) X 6 0 .  F i g u r e 7-  D i s t r i b u t i o n o f F i b r e s i n t h e Copper M a t r i x , Specimen W-l-12, n i t a l e t c h , X 5 0 .  - 22 -  remained v i r t u a l l y c o n s t a n t a t kk.Ofy.  T h i s v a l u e was c a l c u l a t e d u s i n g  the complete c r o s s - s e c t i o n a l a r e a o f t h e composite, i . e . i n c l u d i n g t h e r e l a t i v e l y t h i c k s u r f a c e l a y e r o f copper.  The f i b r e s were c l o s e l y packed  ( F i g u r e 7)-  a t t h e c e n t r e o f t h e composites  A more r e a l i s t i c  packing  f r a c t i o n o f f i b r e s , based on measurements n e a r t h e c e n t r e , i s  2.  O.75.  Size Effects T e n s i l e t e s t s were made on annealed  composite specimens i n  the s i z e range O.O98 i n c h e s t o 0.022 i n c h e s .  Typical  s t r a i n curves f o r two composites,-W-l-A and W-3-A 8a,and 8b. tensile  stress-plastic  a r e shown i n F i g u r e s  These curves a r e p l o t t e d n o t t o f r a c t u r e , b u t t o t h e u l t i m a t e  s t r e s s o f t h e specimens.  Curves o f composite y i e l d s t r e s s and u l t i m a t e t e n s i l e v e r s u s specimen diameter F i g u r e s 9 and 10.  stress  f o r t h r e e d i f f e r e n t composites a r e shown i n  The diameter  of the i n d i v i d u a l s t e e l wires  i s also  p l o t t e d on t h e a b s c i s s a .  I t was observed apparent  that the Ipad-elongation  curves' e x h i b i t e d two  y i e l d p o i n t s ; an i n i t i a l y i e l d p o i n t ( d e s i g n a t e d  w h i c h c o u l d p o s s i b l y be a t t r i b u t e d t o t h e i n i t i a t i o n  . YP.  of flow i n the  m a t r i x , and a second y i e l d p o i n t , ( d e s i g n a t e d P m p o s i t e ) Y  w  n  i  c  C O  corresponded, t o t h e s t a r t o f p l a s t i c  flow throughout  . . )  n  apparently  t h e composite.  The  method o f o b t a i n i n g t h e s e two y i e l d p o i n t s from l o a d - e l o n g a t i o n curves i s shown i n F i g u r e 11.  (Figures 9  a  n  d 10 do not show t h e two y i e l d p o i n t s ;  t h e y a r e p l o t t e d t o s t a r t a t t h e composite y i e l d a plot  of the "matrix y i e l d s t r e s s " versus  stress.)  specimen  F i g u r e 12 shows  diameter.  6d-  I- *  4o\  o W-l-A D W-2-A O W-3-A A  0.0024 in.  individual wire diameters O.O/O  _L  O.OZO  _L  0030  O.Q40  0-050  10.0037  0.0034  0.0027 0.060  0.070  _L  o.C9o  0.080  Specimen D/ometer (inches)  Figure 9  Compost Yield Stress Vs. Specimen Diameter-Composites  ro  W-i-A,W2-A W-3A. 7  43  •  •  •  •  4  o W-l-A O  •  A  W-2-A O W-3-A A  _  A  P A  O nd. wire  lo.0027  d i a ? s — * - 10.0024in  o.ozo  ^~ also  '  oc*o  1  oioso '  |o.0034 0-060  '  0^070 '  0.080  lo.0037 '  Specimen O i a t v e i e r (inches?  Ultimate Tensile Stress Vs.Specimen Diameter, Composites  WH-A,W2A,W-3-A.  ao9o  ro  - 27 -  Elongation V- \ :  ».  Figure 11 Method of Determining ' Y P ^ ^ d'nd-Y P Load-Elongation Curves. ;  0$Me  From  Specimen Diameter (inche s)  Figure 12 Motrix Yield Stress Vs.Specimen Diameter, Composites W-l-A,W-2-A W-3-A. 7  00  - 29 -  An attempt was made t o r e l a t e the. t h i c k n e s s . o f copper on t h e o u t s i d e o f t h e composites t o t h e c h a r a c t e r i s t i c s curves.  of t h e l o a d - e l o n g a t i o n  To t h i s end t h e d i s t a n c e D ( i n F i g u r e 1 1 )  measured i n percentage  e l o n g a t i o n i s shown p l o t t e d . v e r s u s specimen diameter i n F i g u r e  13.  F i g u r e s 8a and 8b i n d i c a t e t h e heterogeneous y i e l d i n g which was found.to occur i n c e r t a i n specimens.  Both t h e e x i s t e n c e and e x t e n t  ©f'this b e h a v i o u r were specimen s i z e dependent i n t h e manner shown i n F i g u r e lk.  Discontinuous  y i e l d i n g was never observed w i t h  g r e a t e r than 0.070 i n c h e s . • The e x t e n t  specimen diameters  o f the phenomenon i n c r e a s e d t o a  maximum.of about kfy ( i n p e r cent e l o n g a t i o n "over a l l / 2 i n c h gauge  length)  a t a specimen diameter o f 0.C47. i n c h e s and t h e n d i m i n i s h e d a t s m a l l e r diameters as shown.  In an attempt t o determine, t h e work-hardening  characteristics  o f t h e composites, v a l u e s - o f n, t h e work-hardening exponent, i n t h e e m p i r i c a l e x p r e s s i o n f o r the flow T-T-  1  ~ were c a l c u l a t e d versus  3.  =  K  i  €  curve n  -  ;  ....-(7)  from t h e s l o p e s o f l o g - l o g p l o t s o f t r u e s t r e s s 1  t r u e s t r a i n ( £ ).  The r e s u l t s  (Table I I ) show.no d e f i n i t e  )  trends.  S t u d i e s o f Heterogeneous Y i e l d i n g The  appearance o f heterogeneous y i e l d i n g i n c e r t a i n  o f composites made from the i n f i l t r a t i o n further  (^  specimens  o f s t e e l wire bundles prompted  s t u d i e s t o determine t h e cause o f t h e phenomenon.  1  §  3-0  5  t.s  8  •  W-l-A  O.S  • W-2-A O" W-3-A A  _L  o.o/o Figure 13  O.&&O  -A-  O.C30 G.040 O.&SO Specimen Dfometer (inches)  Distance D " (Figure 11) V s . Specimen Diameter V  0.060  ao70  o.oao  o.o30  o.o40  o.oso  Specimen Diameter (inches)  Figure  14 Discontinuous Yield Elongation Vs. Specimen Diameter.  0.060  o.oro  -32  -  • TABLE I I . Work-Hardening' Exponents  W-3-A  . w-r-A Specimen-Diameter  n  j  Specimen"Diameter  n  O.O98  0.297  0.070  0.150  O.O89  O..I77  0.060  0.169  0.081  0.125  O.O53  o.io4  0.075  0.213  0.. 032  0.217  O.O67  O.I79  O.OV7  O.O95  O..054  0.174  •  - 33 -  (a) . E f f e c t  o f Cold-Working  - C o l d working  drawing p r i o r t o t e s t i n g removed any t r a c e Reductions  i n a r e a o f as l i t t l e  specimens by wire  of discontinuous y i e l d i n g .  as 2.5$ gave t h i s  (b) P r o p e r t i e s o f S i n g l e S t e e l Wires  result.  - A s i n g l e p i e c e o f the  h i g h carbon s t e e l w i r e was annealed f o r 5 hours a t 680°C and, t e s t e d i n tension.  The same t y p e o f d i s c o n t i n u o u s y i e l d i n g as found i n t h e  composites was f o u n d t o o c c u r but w i t h somewhat s m a l l e r l o a d (Figure 15).  I t i s a l s o i n t e r e s t i n g t o note t h a t  drops,  the s t r a i n hardening  exponent o f t h e annealed w i r e was found t o be 0.167-  (c) E f f e c t  o f Intemgfted; Loading - S e v e r a l t e s t s were stopped  a f t e r d i s c o n t i n u o u s y i e l d i n g was completed L o a d i n g was immediately r e - a p p l i e d  specimens unloaded.  and the t e n s i l e t e s t was a l l o w e d t o  p r o c e e d t o r u p t u r e o f t h e specimen. characteristics  and,the  The y i e l d s t r e s s  o f t h e s e specimens were n o t a f f e c t e d  and  work-hardening  by i n t e r p j p t i n g t h e  loading.  (d) E f f e c t exhibiting  of S t r a i n Ageing  - S e v e r a l specimens a t a s i z e  t h e maximum amount o f d i s c o n t i n u o u s y i e l d i n g ,  were g i v e n s t r a i n a g e i n g t r e a t m e n t s .  The specimens were s t r a i n e d  u n i f o r m d e f o r m a t i o n and work-hardening unloaded as i n s e c t i o n  ( c ) above.  yield  stresses  The samples were t h e n aged f o r e i t h e r The e f f e c t o f a g e i n g on t h e  i s summarized i n T a b l e I I I .  A d i s c o n t i n u o u s y i e l d r e g i o n Was n o t r e s o l v a b l e 1  until  had commenced, and were t h e n  l / 2 o r 1 hour a t 200°C f o l l o w e d by r e t e s t i n g . m a t r i x and composite  i . e . 0.0*4-7 i n c h e s ,  i n specimens  aged f o r 1/2 hour but was d e f i n i t e l y p r e s e n t i n specimens aged f o r 1 hour. A p p r o x i m a t e l y 70$ o f t h e o r i g i n a l e x t e n t o f d i s c o n t i n u o u s y i e l d i n g had  - 34  Figure 15  Stress-Plastic'Strain Curve For Single Steel Wire, Diameter 0 . 0 4 9 i n , Annealed 5hrs at 6 8 0 ° C .  -  -35  -  r e t u r n e d , but w i t h s m a l l e r l o a d d r o p s .  TABLE I I I . • S t r a i n Ageing  Treatment l/2  Y  hour a t 200°C  S  13,300 p . s . i . 34,500 p . s . i .  • A f t e r Ageing  20,000  43,000  Before Ageing  15,900  39,500  21,400  41,500  •After Ageing  (e) O b s e r v a t i o n s D u r i n g - L o a d i n g - T h e : s u r f a c e o f s e v e r a l was  p o l i s h e d w i t h 4/o  C  B e f o r e Ageing  :  1 hour a t 200°G  Y.S.  - -M.  specimens  emery paper and then - observed d u r i n g a ^ t e n s i l e  test.  Deformation bands appeared a t random p o i n t s a l o n g t h e gauge l e n g t h s o f the specimens, curve.  s i m u l t a n e o u s l y w i t h sudden l o a d drops on the l o a d - e l o n g a t i o n  C o n t i n u e d l o a d i n g caused the d e f o r m a t i o n bands t o widen  u n t i l t b e y i n t e r a c t e d w i t h each o t h e r . shown i n F i g u r e 16.  B.  Composites 1.  A shadowgraph o f such a specimen i s  The d e f o r m a t i o n bands are. b a r e l y d i s c e r n i b l e a t the  p e r i m e t e r o f the specimen. deformation f r o n t  visibly  The arrows  i n d i c a t e observed d i r e c t i o n of  motion.  Made:From- S i n t e r e d Armco I r o n Powder  Structures The p r o d u c t o f i n f i l t r a t i n g pure i r o n powder s k e l e t o n s w i t h  liquid  copper f o l l o w e d by f a b r i c a t i o n t o . p r o d u c e . f i b r o u s i r o n i n a.copper-  m a t r i x p r o v e d . t o be more i n t e r e s t i n g and more, u s e f u l t h a n t h a t o b t a i n e d from,steel wire bundles.  One  advantage  o f the powder composites was t h a t  F i g u r e 16.  Deformation Bands on P o l i s h e d S u r f a c e Specimen W-k-L, X  30.  of  - 37 -  c o m p l i c a t i o n s due t o carbon and i t s p a r t i a l d e p l e t i o n d u r i n g a n n e a l i n g t r e a t m e n t s were n o t p r e s e n t .  Additionally,  i t was c o n v e n i e n t t o o b t a i n  much f i n e r f i b r e s by t h e powder approach.  •Photomicrographs shown i n F i g u r e 17. powder f r a c t i o n s  o f some powder comppsites a f t e r drawing a r e  The m a t e r i a l s shown were made from t h e two d i f f e r e n t  -100  +150  mesh and -325 mesh.  on composite specimens o f d i a m e t e r d i a m e t e r o f the f i b r e s and  M e t a l l o g r a p h i c measurements  0.035 i n c h e s gave, f o r t h e average  (a) 10 microns f o r t h e c o a r s e r powder composites  (b) a p p r o x i m a t e l y 2 microns f o r the f i n e r powder composites.  p r o b a b i l i t y t h a t a f i b r e would l i e i n t h e p l a n e o f p o l i s h i n g e n t i r e l e n g t h was n e g l i g i b l e .  The  over i t s  Consequently,. m e t a l l o g r a p h i c measurements  c o u l d n o t be expected t o g i v e an a c c u r a t e i n d i c a t i o n o f the l e n g t h s o f fibres.  However an e s t i m a t e of f i b r e l e n g t h s can be made from t h e i r  diameters, as w i l l be d i s c u s s e d l a t e r .  2.  • Size  Effects  Tensile  t e s t s were done on  -100 +I50 mesh powder composites a t  v a r i o u s s t a g e s o f r e d u c t i o n t o determine t h e e f f e c t o f s p e c i p e n and f i b r e diameter i n much the same way as f o r the s t e e l w i r e composites. Typical  s t r e s s - p l a s t i c s t r a i n c u r v e s f o r some specimen s i z e s a r e shown  i n F i g u r e s l 8 a and l 8 b .  Plots  o f u l t i m a t e t e n s i l e s t r e s s and composite  y i e l d s t r e s s v e r s u s specimen d i a m e t e r a r e shown i n F i g u r e s 19 and 20. Only a s l i g h t i n c r e a s e i n s t r e n g t h w i t h d e c r e a s i n g composite was suggested by t h e d a t a .  diameter  -  F i g u r e 17.  3  8  S e c t i o n s t h r o u g h I r o n Powder Composites, iSpecimen diameter i n c h e s , annealed hour a t 6 8 0 ° C , 2$ n i t a l e t c h , (a) - 1 0 0 + 1 5 0 mesh, X 2 6 , (b) - 1 0 0 + 1 5 0 mesh, X 2 0 0 , (c) - 3 2 5 mesh, X kj, (d) - 3 2 5 mesh X 2 0 0 . 0  .  0  3  5  1  -  - 39  -  50\0.077  AOr-  30 cL  •n  0 X  b 20  to I  I  I  I  I  l_  IS  16  Figure IB'Stress-PI o she Strom Curves For Various Specimen Dameters - 1 0 0 + 1 5 0 Mesh Powder Composites  -kO -  70  •I a  Powcter No 2 O Powder No 3 A 30  OOJO  O.OSO  &oao  C&fO  O.OS0  0-060  O.OTO  O.OSO  Specimen Diameter (inches)  Figure 19  U.T.S. Vs. Specimen Diameter,-100+150  Mesh Powder Composites  C090  I  -p-  -  4  3  -  The l o a d - e l o n g a t i o n curves f o r a l l t h e powder composites were such as t o i n d i c a t e a s i n g l e y i e l d p o i n t r a t h e r than two as observed f o r the s t e e l wire composites.  Consequently t h i s one y i e l d p o i n t has  been d e s i g n a t e d as YP^ ^ ^ composite i • Work-hardening exponents diameters.  I f heterogeneous  were c a l c u l a t e d a t v a r i o u s  y i e l d i n g was p r e s e n t the  work-hardening  exponent was c a l c u l a t e d from t h a t p a r t o f the. f l o w curve f o l l o w i n g completion of discontinuous y i e l d i n g .  specimen  immediately  F o r t h i s purpose, t h e  p o i n t o f z e r o p l a s t i c s t r a i n was a r b i t r a r i l y t a k e n as b e i n g a t t h e end of the discontinuous y i e l d i n g r e g i o n .  The r e s u l t s a r e t a b u l a t e d i n  T a b l e IV. •TABLE.IV. Work-Hardening Exponents Powder No. 3 Specimen Diameter O.O77 i n c h e s  n  0  .  1  O . O 6 9  0  O.O59 0.046  1 .  5  1  1  7  0.149 0  .  1  4  5  0  .  0  5  4  0  .  1  0  0  0  .  0  2  5  0  .  1  2  1  As i n t h e case o f t h e s t e e l w i r e composites, no d e f i n i t e t r e n d i n these v a l u e s was  3.  apparent.  Heterogeneous Y i e l d i n g D i s c o n t i n u o u s y i e l d i n g was sometimes observed w i t h powder  The e x t e n t o f t h e phenomenon was markedly w i r e composites  composites.  l e s s than that obtained i n s t e e l  and seemed t o be v i r t u a l l y random i n i t s dependence on  - 44 -  specimen d i a m e t e r .  S o l d working o f t h e powder specimens (as l i t t l e as  2%) p r i o r t o t e s t i n g e l i m i n a t e d  any t r a c e o f d i s c o n t i n u o u s  4. Heat Treatments on S a t u r a t e d  yielding.  Iron-Powder Composites  V a r i o u s heat t r e a t m e n t s were c a r r i e d out on t h e powder composites. Specimens were i n i t i a l l y s o l u t i o n t r e a t e d t o s a t u r a t e  the i r o n f i b r e s with  1020°C and were t h e n c o o l e d a t v a r y i n g r a t e s .  copper a t  Several d i f f e r e n t  secondary t r e a t m e n t s were a l s o a p p l i e d i n c e r t a i n c a s e s . t r e a t m e n t was g i v e n  A carburizing  t o one s e r i e s o f specimens i n an attempt t o a s c e r t a i n  the p o s s i b l e e f f e c t o f carbon a d d i t i o n s t o t h e i r o n f i b r e s .  (a). R e s u l t s w i t h  -100 +I50  mesh powder composites - A l l t h e  f o l l o w i n g r e s u l t s a r e from specimens w h i c h had been s o l u t i o n t r e a t e d under d r y hydrogen f o r 15 hours a t 1020°C, t h e n c o o l e d as i n d i c a t e d .  The e l o n g a t i o n s  point t o the ultimate  reported  tensile stress.  a n d . f u r t h e r heat  treated  a r e as measured from t h e y i e l d The gauge l e n g t h used i n a l l cases  was 1 i n c h . (i) "Aircooled"  Specimen Diameter  0.035 0.035 0.035  (120 t o 180°C p e r second)  U.T.S, lbs/in , 2  138,000 140,500 141,500  Y.S. lbs/in  EtLong. 2  108,300 110,200 119,500  $  12.2 14.1  11.7  A photomicrograph o f t h e c o r r e s p o n d i n g s t r u c t u r e Figure  21.  i s shown i n  Figure 21.  Photomicrograph o f - 1 0 0 +150 mesh Powder Composite " a i r c o o l e d " from 1020°C, 2$ n i t a l e t c h , X 2 ^ 0 .  - 46 " A i r c o o l e d " and Reheated 1 hour a t 400°C  (ii)  Specimen Diameter  U.T.S. lbs/in  Y.S. lbs/in  2  135,700 138,000  0.035 0.035  Elong. i  2  123,500 127,700  13.0 13.0  No d i s c o n t i n u o u s y i e l d i n g was observed i n specimens from ( i ) o r ( i i ) above.  " A i r c o o l e d " and Reheated 1 hour a t 750°C  (iii)  D i s c o n t i n u o u s y i e l d i n g o c c u r r e d i n t h e s e specimens.  Specimen Diameter  Y.S. lbs/in  59,600 61,500  47,800 49,000  2  0.035 " 0.035  (iv)  U.T.S. lbs/in :  2  Elong. . i  • Discontinuous; Y i e l d Elong. %  22.7 23.1.  2.2 1,8  " A i r c o o l e d " and C o l d Drawn  S e v e r a l specimens were s a t u r a t e d , " a i r c o o l e d " and drawn c o l d t o obtain--^.n a d d i t i o n a l 40% r e d u c t i o n i n a r e a . • They were t h e n a n n e a l e d 1. hour a t 250°C t o i n d u c e r e c r y s t a l l i z k t i o n o f t h e m a t r i x .  Specimen Diameter' 0.035 O.O35 0.035 0,035  ' U.T.S. lbs/in  Y.S. lbs/in  163,000 173,000 178,000 173,000  .56,200 55,100 79,000 64,300  2  :  Elong. %  2  .  5.8 5.2 5.2 5-1  (v) "Aircooled" Reheated at 400°C, and Cold Drawn Several specimens were saturated, "aircooled", reheated 1 hour at  400°C, drawn an a d d i t i o n a l 40% reduction i n area and annealed 1 hour  at  250°C.  - 4  Specimen Diameter  U.T.S. lbs/in 2  175,500 179,500  O.O35 0.035  Y.S. lbs/in  7  -  Elong. $'  2  88,400. 72,800  4.4 5.4  ( v i ) Quenched i n L i q u i d N i t r o g e n and Aged a t Room Temperature S a t u r a t e d and " a i r c o o l e d " specimens were r e h e a t e d t o 1020°C f o r 20 minutes f o l l o w e d by r a p i d quenching i i i a b a t h o f l i q u i d n i t r o g e n (-196°C). The  specimens were t h e n a l l o w e d t o r e h e a t t o room temperature, and were  h e l d t h e r e f o r v a r i o u s times p r i o r t o t e s t i n g .  A l l specimens were found  t o be magnetic a t -196°C .  Specimen - Diameter 0.035 0.035 0.035 0.055 0.035 0.035  Aging Time 0 hrs 0 -3 24 100 300  U.T.S. lbs/in  2  107,700 104,500 ,120,800 121,000 •133,000 130,500 '  Y.S. lbs/in 84,200 86;200 94,100 106,700 118,500 76,000  Elong. 2  1.0 1.4 6.5 6.0 5.7 2.4  ( v i i ) Slow c o o l e d from 1020°C Two specimens were s e a l e d o f f , i n a f u s e d q u a r t z tube under vacuum. box  The s e a l e d tube was p l a c e d i n the c e n t r e o f a r e s i s t a n c e - h e a t e d  f u r n a c e and surrounded by r e f r a c t o r y b r i c k s .  S o l u t i o n treatment  was c a r r i e d out a t 1020°C f o r 15 hours and., t h e m the f u r n a c e was shut o f f .  ;  power s u p p l y t o t h e  The maximum r a t e o f c o o l i n g e x p e r i e n c e d between  1020°C and 25°C, was 2°C/minute.  -  Specimen Diameter 0  .  0  3  5  0  .  0  3  5  Y.S.  U.T.S. lbs/in 5  0  ,  8  0  0  H - 9 , 9 0 0  Discontinuous Y i e l d E l o n g . <j  3  9  ,  2  0  0  2  8  .  0  2 . 4  3  9  ,  3  0  0  2  6  .  8  2  Representative s t r e s s - p l a s t i c heat t r e a t m e n t s  Elong.  lbs/in2  2  .  1+8 -  0  9  s t r a i n curves f o r t h e v a r i o u s  a r e shown i n F i g u r e . 2 2 .  The work-hardening exponents  a r e shown w i t h each c u r v e .  (b) R e s u l t s w i t h - 3 2 5 solution  treatment  a marked l o s s resulting  mesh Powder Composites - D u r i n g t h e  o f a l l composites  of.continuity  produced  i n t h e f i b r e s was found t o o c c u r .  s t r u c t u r e (shown i n F i g u r e 2 3 ^  .'from t h a t o f composites that disintegration  made from wire o r c o a r s e r powders.  o f the f i b r e s i n f i n e powder composites  f r a c t i o n of the i r o n present during s o l u t i o n discontinuity  It i s likely i s associated  ( i n i t i a l l y not saturated  which might be capable o f d i s s o l v i n g  1 0 2 0 ° C )  The  was c o n s i d e r a b l y d i f f e r e n t  w i t h the r e l a t i v e l y h i g h volume p e r cent o f copper with iron at  mesh i r o n powder,  from.-325  treatment.  an appreciable, Because o f the  o f many o f the f i b r e s i n these composites,  i t may not be  j u s t i f i e d . t o compare the r e s u l t s which f o l l o w w i t h those o b t a i n e d f o r t h e c o a r s e r powder m a t e r i a l s .  •  (i) "Airepoled"  Specimen Diameter  U.T.S. Ibs/in2  0  .  0  3  5  1  2  2  ,  7  0  0  0  .  0  3  5  1  2  0  ,  7  0  0  Y.S. lbs/in  .Elong. 2  .114,000 1  1  1  ,  0  0  0  1  2  .  0  1  2  .  6  160-  n -  0.222 Aircooled From'' 1020°C  140  Oufcnched in Liq N From 1020 °C z  n= 0.167  &  Slow Cooled F r o m I 0 2 0 ° C at ^ l°c/mfn  rvO.179  to  j  Fqure 22  L  J  6  1  T  i S  9  /b,/..  £ (%)  ^  i3  i4  ,4f  13  15  ,e  16  N  Nf  2  5  Stress Plastic Strain Curves For Representative H e a t T r e a t m e n t s M e s h Fbwder  Composites  J  L  *°*7 On-100+150  -  Figure 2 5 .  Photomicrograph of - 3 2 5 mesh Bowder Composite Quenched i n l i q u i d nitrogen and aged f o r 1 hour at - 8 0 ° C . P i c r i c etch, X llkO.  5  0  - 51 ( i i ) . C o o l e d a t Rates o f i t o  25 C/second q  Whereas the "aircooled'.! specimens were withdrawn a d i s t a n c e o f 12 i n c h e s from the hot zone o f the f u r n a c e i n 4 seconds, f o r a c o o l i n g r a t e o f 120 t o l80°G/§eeond,  ( E x p e r i m e n t a l Procedure,. S e c t i o n  t e s t s were a l s o made on specimens which were withdrawn  D.)  from the f u r n a c e  a t slower r a t e s t o determine the e f f e c t o f r a t e o f c o o l i n g from the s o l u t i o n temperature.  i - 30 seconds w i t h d r a w a l time ( e s t i m a t e d c o o l i n g r a t e l g t o 25°'C/sec.) Specimen Diameter  0.035 0.035  U.T.S. lbs/in 2  122,800 116,300  Y.S. lbs/in  Elong.  i  2  113,700 110,100  15.5 1A.5  - 14 minutes w i t h d r a w a l time ( e s t i m a t e d c o o l i n g r a t e l / 2 t o l C / s e c . ) q  Specimen Diameter  0.035 0.035  U.T.S. lbs/in 2  78,000 78,000  Y.S. lbs/in  Elong.  i  2  Discontinuous Y i e l d Elong. %  10.5 9-9  66,700 67,900  0.7 0.7  ( i i i ) Furnace C o o l e d . A f t e r s o l u t i o n t r e a t m e n t i n a tube f u r n a c e , some specimens left  i n the hot zone a f t e r t h e power t o the f u r n a c e was  r a t e o f c o o l i n g was  were  c u t o f f . The average  500°C p e r hour f o r the f i r s t hour, and became  increasing-  \ ly  slower as 30°C was  approached.  Specimen Diameter  0.035 0.035  U.T.S. lbs/in 2  64,500 64,500  Y.S. lbs/in  52,600 52,000  •Elong 2  •*  28.3 26.6  Discontinuous Y i e l d Elong. %  3.5 2.8  -52. ( i v ) . Quenched i n L i q u i d ' N i t r o g e n S e v e r a l s o l u t i o n t r e a t e d specimens were quenched i n n i t r o g e n from 1020°C, then; brought t o room temperature and  liquid  tested within  5 minutes. Specimen • Diameter  0.035 0.035  (v)  U.T.S. lbs/in  Y.S. lbs/in  2  at  ••*  6.1 8.0  105,000  110,400 110,400  104,000  Quenched i n L i q u i d N i t r o g e n and  Specimens were quenched t o age  Elong. 2  -80°C f o r v a r i o u s t i m e s as  Specimen Diameter  0.035 0.035 0.035 0.055 0.035  Aged a t  -196°C, t h e n a l l o w e d t o  i n d i c a t e d below,, (see  Ageing • Time  U.T.S. lbs/in  Y.S. lbs/in  10 30 .1 3 6  118,700 111,000 117,000 114,700 111,200  111,800 105,000 110,200 106,800 106,500  min. hr.  -80°C.  2  reheat  also' Figure  and 25).  Elong. 2  11.2. 10.5 10.7 11.7 7.9  ( v i ) C a r b u r i z e d a t 920°C. Specimens were "pack" c a r b u r i z e d as  outlined i n Experimental  Procedure f o r v a r i o u s t i m e s . Specimen Diameter  Carburizing Time  U;T,S. lbs/in  = . 5 min. on  125,900 118,000 118,800 126,500 109,800 110,100  0.035 0.035 0.035 O.O55  0.055 0.035  ,  o n  2  Y.S. lbs/in  119,500 109,700 105,000 109,200 73,800 72,200  Elong. 2  16.9 10.2 7.0 6.8 1.6 1.3  The  e f f e c t o f l o n g c a r b u r i z i n g times  i s shown i n F i g u r e 24. associated  on t h e m i c r o s t r u c t u r e  I t seems l i k e l y t h a t t h e l a r g e pores a r e  w i t h t h e l i b e r a t i o n o f d i s s o l v e d gas o n - c o o l i n g from t h e  carburizing  temperature.  R e p r e s e n t a t i v e s t r e s s - p l a s t i c s t r a i n curves f o r t h e above mentioned heat t r e a t m e n t s  a r e shown i n F i g u r e J  25 a l o n g w i t h t h e  c o r r e s p o n d i n g work-hardening exponents. • F i g u r e 26 shows t h e v a r i a t i o n of the y i e l d cooling  rate.  stress  of s o l u t i o n t r e a t e d  i r o n powders composites  with  -  F i g u r e 2k.  5  4  -  Photomicrograph o f -325 mesh Powder Composite, Pack c a r b u r i z e d a t 920°C f o r 100 minutes, unetched. X 65.  n = 0-047  hgure25_ Stress-Plastic Strain  Curves-Representative Heat Treatments O n - 3 2 5 Mesh Powder Composites  Log Cooling Rote °C/Sec.  Figure 2 6  Y. S . V s . C o o l i n g R a t e For S a t u r a t e d  !  lron Powder C o m p o s i t e s  57  -  IV.  A.  -  DISCUSSION  . S t r u c t u r e s and A s p e c t R a t i o s o f  Composites  B o t h methods used t o produce a m e t a l f i b r e r e i n f o r c e d p r o v e d t o be s u i t a b l e t o some e x t e n t .  F o r t h e purpose o f  o b j e c t i v e o f t h i s work, however, t h e powder t e c h n i q u e was  composite  fulfillingithe~ superior.  Much  f i n e r f i b r e s c o u l d be p r o d u c e d and a s p e c t r a t i o s and i n t e r f i b r e s p a c i n g s c o u l d be e a s i l y v a r i e d o v e r a wide range.  In a d d i t i o n , the m a t e r i a l p r e -  p a r e d from pure i r o n powders" i n v o l v e d . o n l y two components, and was t u r a l l y s i m p l e r t h a n t h a t p r e p a r e d from h i g h c a r b o n s t e e l w i r e .  struc-  That t h e  f i b r e s i n specimens made f r o m t h e c o a r s e r i r o n powder compacts d i d i n f a c t have f a v o u r a b l e a s p e c t r a t i o s can r e a d i l y be p r o v e d .  The d i a m e t e r s o f t h e  f i b r e s a r e known as. t h e y were measured m e t a l l o g r a p h i c a l l y .  .However  >  as  mentioned p r e v i o u s l y , t h e l e n g t h s o f t h e f i b r e s c o u l d n o t be o b t a i n e d by metallographic examination.  None t h e l e s s , t h e volume o f each i r o n p a r t i c l e  i s c o n s t a n t , and assuming t h a t d u r i n g t h e f a b r i c a t i o n p r o c e s s t h e shape o f t h e i r o n p a r t i c l e changes f r o m a sphere t o an e l l i p s o i d o f minor a x i s  a=b  and major a x i s c, t h e n ,  Volum^e o f f i b r e  V  f  =  h fjTabc 3  =  k 3  Tf a c 2  =  k rf r 3  3  where r i s t h e o r i g i n a l i r o n sphere d i a m e t e r . . T h e r e f o r e t h e a s p e c t  4  *  r a t i o of the f i b r e s i s «  £ = r ^ . I f t h e d i a m e t e r o f a specimen was a a3 ' reduced by a f a c t o r o f 10 t h e n " a " o f t h e f i b r e = r _ , t h e r e f o r e e,, ='1000. 10 • a" ( I t s h o u l d be n o t e d t h a t a . i s t h e . maximum d i a m e t e r o f t h e f i b r e . . The  average d i a m e t e r would be somewhat s m a l l e r . )  Using t h i s treatment, the  a s p e c t r a t i o o f t h e f i b r e s a t a specimen d i a m e t e r o f  0;080 i n c h e s isv,ih ...  t h e o r y , n o t l e s s t h a n 185:1. . S u b s t i t u t i n g . t h i s v a l u e i n t o t h e e q u a t i o n f o r t h e c r i t i c a l a s p e c t r a t i o ( e q u a t i o n 5) g i v e s f o r t h e s h e a r s t r e n g t h r e q u i r e d  - 58-  at the f i b r e - m a t r i x i n t e r f a c e  nr '•  L  where  •  1  rr  l  IB5  ?  f =  f  7H0"  Xl^. is. the t e n s i l e s t r e s s i n the f i b r e s .  Thus, o v e r  the specimen s i z e range i n v e s t i g a t e d a.maximum shear s t r e n g t h o f i s required i n theory f o r f u l l f i b r e reinforcement. i n an i r o n f i b r e encountered  240,000 a  0.080  psi.  The h i g h e s t s t r e s s  i n t h i s i n v e s t i g a t i o n i s i n the order of  Consequently,..the  maximum shear s t r e s s r e q u i r e d , even f o r  .inch-diameter specimen i s i n t h e o r d e r o f  325 p s i .  shear y i e l d s t r e s s f o r pure annealed p o l y c r y s t a l l i n e copper  5,000  Since the i s approximately  p s i , t h e a s p e c t r a t i o s i n a l l coarse i r o n powder composites  i n v e s t i g a t i o n a r e b e l i e v e d t o be f a v o u r a b l e . the f i b r e s remain continuous  in.this  The above a n a l y s i s assumes t h a t  d u r i n g . f a b r i c a t i o n , which may n o t be t r u e ^  However, t h e e s t i m a t e o f shear s t r e n g t h i s c o n s e r v a t i v e l y h i g h due t o t h e n a t u r e o f t h e o t h e r assumptions  used.  C l e a r l y t h e a s p e c t r a t i o s o f f i b r e s i n s a t u r a t e d composites duced, from  pro-  ^325 mesh i r o n powder were much l e s s than d i s c u s s e d above  ( F i g u r e 23).  An e s t i m a t e o f t h e a s p e c t r a t i o i n t h i s case i s v e r y  difficult  t o make, s i n c e t h e c o a r s e r o f t h e f i b r e s p r e s e n t d i d r e t a i n a h i g h r a t i o . Another f e a t u r e o f the f i n e r powder composites f r a c t i o n o f i r o n was p r e s e n t  (  57$) •  The a s p e c t r a t i o i n composites  prepared  w i r e s was a p p r o x i m a t e l y 200. i n a s - i n f i l t r a t e d l e n g t h (2 i n c h e s ) .  is. t h a t a s m a l l e r volume  from h i g h carbon  steel  specimens o f normal t e s t  W i t h r e d u c t i o n o f t h e i n f i l t r a t e d m a t e r i a l by swaging  and drawing t h e l e n g t h o f f i b r e s i n a t e s t specimen cannot  i n c r e a s e , and  - 59  the a s p e c t r a t i o i s t h e n p r o p o r t i o n a l t o d ^  "2  (d^ = f i b r e diameter).  .Thus a 90 p e r cent r e d u c t i o n i n a r e a o f the composite most a 90 p e r cent i n c r e a s e i n the a s p e c t r a t i o .  produces a t  A g a i n , however, t h e r e  i s the p o s s i b i l i t y t h a t the o r i g i n a l w i r e s do not remain d u r i n g r e d u c t i o n o f t h e composite.  -  continuous  Indeed, 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  o f as-drawn m a t e r i a l i n d i c a t e t h a t some w i r e breakage  d i d occur during  f a b r i c a t i o n . Thus i t seems u n l i k e l y t h a t the a s p e c t r a t i o i n w i r e composites was.ever much g r e a t e r than-200.  A t t h i s r a t i o , the maximum  shear s t r e n g t h r e q u i r e d a t the f i b r e m a t r i x i n t e r f a c e s h o u l d not have .exceeded  .B.  300-psi.  Y i e l d i n g Behaviour o f U n s a t u r a t e d Powder  Composites  1. . Heterogeneous Y i e l d i n g Heterogeneous y i e l d i n g , i n v o l v i n g r e l a t i v e l y s m a l l l o a d drops, was  d e t e c t e d i n some composites produced  o f the phenomenon was  from i r o n powder.  not r e l a t e d t o specimen  size.  The  In the case o f  s a t u r a t e d , h e a t - t r e a t e d m a t e r i a l , i t o n l y o c c u r r e d i n annealed of l o w . y i e l d s t r e s s . y i e l d i n g was  There was  i n any way  occurrence  specimens  no e v i d e n c e t o suggest t h a t the d i s c o n t i n u o u s -  due t o breakage  of i n d i v i d u a l f i b r e s or t o a l o s s  o f bonding a t the f i b r e m a t r i x i n t e r f a c e s . - In f a c t , f i b r e breakage cause  s e r r a t i o n s i n the s t r e s s - s t r a i n curve a t the u l t i m a t e s t r e s s  would (as Q  observed by McDanels e t a l . w i t h c o p p e r - r e i n f o r c e d t u n g s t e n f i l a m e n t s ) and not a t t h e y i e l d s t r e s s . powder composites  Thus, the heterogeneous  y i e l d i n g observed.in  i s b e l i e v e d , t o be o f the type n o r m a l l y observed i n  annealed i r o n and low-carbon  s t e e l , and t o be a t t r i b u t a b l e t o the l a r g e  volume f r a c t i o n o f i r o n ( o r the b . c . c . s o l u t i o n o f copper i n i r e n } which i s p r e s e n t i n these  composites.  - 60 -  2.  S i z e Dependence o f Y i e l d  Stress  F i g u r e 20 r e v e a l s - t h a t o n l y a s l i g h t o c c u r r e d i n u n s a t u r a t e d powder composites d e c r e a s i n g specimen  increase i n y i e l d  stress  (from coarse powders) w i t h  d i a m e t e r over the s i z e range  investigated; i . e .  c o r r e s p o n d i n g t o a range o f i n d i v i d u a l f i b r e diameters o f a p p r o x i m a t e l y 26 t o 7 m i c r o n s .  There a r e s e v e r a l . p o s s i b l e reasons f o r t h e i n c r e a s e  observed. a) There i s a t r u e s i z e e f f e c t w i t h i n . t h e i r o n f i b r e s t h i s s i z e range,  over  (a t r u e s i z e e f f e c t b e i n g one which i s d i r e c t l y a f u n c t i o n  o f t h e d i a m e t e r such as t h e s t r e n g t h o f a w h i s k e r . ) .  There was no  a p r i o r i r e a s o n , however, t o expect such a s i z e e f f e c t  i n a mixture o f  d u c t i l e phases, and i t i s u n l i k e l y t h a t such an e f f e c t  i s involved.  b) The m a t r i x mean f r e e p a t h d e c r e a s e s as t h e composite i s reduced i n d i a m e t e r .  Thus, s t r e n g t h e n i n g o f t h e m a t r i x might be e x p e c t e d "  due t o a r e d u c t i o n i n t h e p a t h l e n g t h a v a i l a b l e f o r d i s l o c a t i o n p i l e - u p during i n i t i a l p l a s t i c  strain  c) As t h e composite  (i.e. a grain size effect  exists),  i s reduced i n s i z e , t h e d i s s o l v e d  copper  c o n t e n t o f t h e i r o n f i b r e s i n c r e a s e s w i t h t h e acciamulationnQf a n n e a l i n g time a t 680°C.  However, t h e maximum s o l u b i l i t y o f copper i n i r o n a t  680°C i s r e p o r t e d t o be 0 . 5 p e r c e n t . i s e x h i b i t e d by a l l o y s effect  i n this  in this  system i s s m a l l .  Moreover, a l t h o u g h age-hardening  c o m p o s i t i o n range, t h e s o l u t i o n h a r d e n i n g "  '  I t t h e r e f o r e seems p r o b a b l e t h a t much o f t h e 17.5-. V increase i n y i e l d  er  cent  s t r e n g t h shown i n F i g u r e 20 i s due t o (b) w i t h a  c o n t r i b u t i o n from ( c ) .  - 61 C.  Yield. Behaviour o f Wire  Composites  1. • O r i g i n o f Two Y i e l d P o i n t s The l o a d - e l o n g a t i o n c u r v e s f o r t h e w i r e composites two apparent y i e l d p o i n t s , ^Pmatrix  a n <  ^ ^composite*  exhibited  The c o r r e s p o n d i n g  "matrix y i e l d s t r e s s " i n c r e a s e d f a i r l y r a p i d l y w i t h d e c r e a s i n g diameter  (Figure 12).  specimen  C o u p l i n g t h i s w i t h t h e o b s e r v a t i o n s shown i n  F i g u r e 1 J , i n which t h e t h i c k n e s s o f t h e copper c o a t i n g on the o u t s i d e o f t h e specimen  i s r e l a t e d t o specimen  diameter,, suggests t h a t t h e  i n i t i a l y i e l d i n g observed was due t o a g r i p e f f e c t .  I t i s suggested  t h a t t h e copper c o a t i n g y i e l d e d i n t h e g r i p s g i v i n g r i s e t o . Y P ^ - t r i x • -As e v i d e n c e o f t h i s , a t s m a l l e r specimen;.; d i a m e t e r s c o r r e s p o n d i n g t o t h i n n e r copper c o a t i n g s , t h e m a t r i x y i e l d s t r e s s r o s e , p r o b a b l y due t o increasing restraint  from t h e s t e e l f i b r e s .  diameters t h e m a t r i x y i e l d stress.became which has. been termed  t h e composite  In f a c t , at small  specimen  very close i n value t o that  yield stress.  Consequently,  i t is  believed that only the l a t t e r y i e l d stress i s t r u l y i n d i c a t i v e of t h e p r o p e r t i e s o f t h e composites.  2.  Heterogeneous Y i e l d i n g The  e x t e n t o f heterogeneous  d i s t i n c t l y r e l a t e d : t o composite  y i e l d i n g i n wire composites  diameter  (Figure 14).  was  The phenomenon  was a l s o much more marked i n w i r e than i n powder composites.  Since  d i s c o n t i n u o u s y i e l d i n g was o n l y observed i n m a t e r i a l s o f r e l a t i v e l y low composite  y i e l d s t r e s s , i t i s u n l i k e l y t h a t i t can be a t t r i b u t e d even  p a r t i a l l y t o a grip effect) i . e . irregular grip slippage. o f f i b r e s would be expected, t o cause s e r r a t i o n s t o appear s t r a i n curve a t h i g h e r s t r e s s e s  8  Also,  breakage  i n the s t r e s s  ratherr. than j u s t a t t h e onset o f y i e l d i n g .  - 62 -  I t was  demonstrated t h a t a s i n g l e , s p h e r o i d i z e - a n n e a l e d , s t e e l  w i r e e x h i b i t e d d i s c o n t i n u o u s y i e l d i n g o f the type observed i n m i l d  steel.  23  I t has been s t a t e d elsewhere  that a spheroidized eutectoid i n a high  carbon s t e e l can e x h i b i t the phenomenon, whereas a p e a r l i t i c o f t h e same o v e r a l l c o m p o s i t i o n does n o t .  structure  Bredz and Schwartzbart  have  observed a d e c a r b u r i z i n g phenomenon when copper was melted i n c o n t a c t w i t h s t e e l s o f v a r i o u s carbon c o n t e n t s .  The carbon (due. t o the i n f l u e n c e o f  the copper) became c o n c e n t r a t e d a t the g r a i n b o u n d a r i e s of,'the s t e e l . i  The Q.012  i n c h e s d i a m e t e r s t e e l w i r e s c o n t a i n e d i n the composites  used i n t h i s i n v e s t i g a t i o n were i n c o n t a c t w i t h l i q u i d copper a t 2100°F f o r 10 minutes f o l l o w e d by quenching.  I r o n a t t h i s temperature can c o n t a i n 17  up t o 8.5 p e r c e n t copper i n s o l u t i o n .  I t has been s t a t e d  elsewhere  t h a t a -100 +150 mesh pure i r o n powder composite becomes s a t u r a t e d w i t h copper i n a p p r o x i m a t e l y 200 minutes  o f i n f i l t r a t i o n time a t 1100°C, . Thus,  due t o t h e l a r g e s i z e o f t h e i n d i v i d u a l w i r e s and r e l a t i v e l y s h o r t time i n contact w i t h l i q u i d . c o p p e r , i t i s f e l t that only the surface of t h e wires Vas i n i t i a l l y s a t u r a t e d with copper. p r i o r t o the i n i t i a l  The s t r u c t u r e o f the s t e e l f i b r e s t h e n ,  swaging o p e r a t i o n , was  tempered  m a r t e n s i t e (quenching  from 1150°C f o l l o w e d by tempering a t 680°C). Experiments i n v o l v i n g t h e e f f e c t o f c o l d work and s t r a i n a n n e a l i n g i n d i c a t e d , t h a t heterogeneous y i e l d i n g i n the wire composites might be o f the normal m i l d s t e e l type observed i n s p h e r o i d i z e d : h i g h - c a r b o n s t e e l s . However, the s i z e dependence o f the phenomenon i s not a d e q u a t e l y e x p l a i n e d on t h i s b a s i s .  Moreover,  the f a c t t h a t a marked decrease i n w i r e  y i e l d s t r e n g t h o c c u r r e d a t s i z e s where heterogeneous suggests t h a t a n o t h e r mechanism may  y i e l d i n g was  be i n v o l v e d i n the p r o c e s s .  composite a maximum  I t i s proposed; t h a t much o f the d i s c o n t i n u o u s  y i e l d i n g i n wire  composites i s a t t r i b u t a b l e t o s h e a r i n g a t t h e m a t r i x - f i b r e i n t e r f a c e s . W i t h p r o g r e s s i v e r e d u c t i o n and a n n e a l i n g  o f t h e composite, carbon-segregates 24,  to the s t e e l wire  surfaces  (as p e r Bredz and Schwartzbart  appears as g r a p h i t e a t t h e i n t e r f a c e .  ) and e v e n t u a l l y  The f a c t t h a t t h i s phenomenon would  be dependent on t o t a l ' . a n n e a l i n g time and hence specimen diameter accounts f o r the o b s e r v e d - v a r i a t i o n i n e x t e n t specimen s i z e shown i n F i g u r e lk.  o f the discontinuous  Thus, w i t h d e c r e a s i n g  yielding  with  composite diameter,  down, t o about Q'i046 i n c h e s , t h e f r a c t i o n o f t o t a l i n t e r f a c e a r e a on which s h e a r i n g can occur i s i n c r e a s i n g . the m a t r i x  Below t h i s s i z e , s e p a r a t i o n over a l l  f i b r e i n t e r f a c e s occurs a f t e r p r o g r e s s i v e l y l e s s t o t a l  strain.  T h i s argument p r e d i c t s t h a t below,0.046 i n c h e s diameter, t h e t e n s i l e on t h e composites i s b e i n g c a r r i e d e n t i r e l y by t h e m a t r i x of flow.'  load  i n the e a r l y  The s t r a i n - h a r d e n i n g b e h a v i o u r ( T a b l e I I , page 32) does, not  stages support  t h i s model t o o w e l l , however. The  observed e f f e c t s o f a g e i n g and c o l d work can be r a t i o n a l i z e d  i n terms o f t h e proposed i n t e r f a c e - s h e a r mechanism. which e x h i b i t e d t h e maximum amount o f d i s c o n t i n u o u s c o l d working o f t h e specimen t o a r e d u c t i o n o f 4-1/2 eliminated the discontinuous  A t t h e specimen d i a m e t e r y i e l d i n g , i . e . 0.6k6  inches,  p e r cent not o n l y  y i e l d i n g but a l s o r a i s e d the y i e l d s t r e s s t o  44,000 p s i which i s an i n c r e a s e o f a p p r o x i m a t e l y annealed c o n d i t i o n ( F i g u r e 9 ) .  33 p e r cent o v e r the  T h i s i m p l i e s t h a t c o l d w o r k i n g has p a r t i a l l y  r e s t o r e d t h e bond between the f i b r e s and t h e m a t r i x , down g r a p h i t e o r o t h e r i n t e r f e r i n g l a y e r s .  by m e c h a n i c a l l y  breaking  A g e i n g o f specimens i n t h i s  s i z e range f o r 1 hour a t 200°C p a r t i a l l y r e s t o r e d t h e d i s c o n t i n u o u s  yielding  - 6k w h i l e a l s o s l i g h t l y r a i s i n g t h e composite 6 per cent).  y i e l d s t r e s s (by a p p r o x i m a t e l y  A c c o r d i n g t o t h e i n t e r f a c e - s h e a r argument a b o v e , t h i s  would i m p l y t h a t the a g e i n g treatment has a l l o w e d the c r e a t i o n o f new  ;  shear p o i n t s o r a r e a s which shear a t h i g h e r s t r e s s v a l u e s t h a n i n the initial  specimen.  . O p t i c a l m i c r o s c o p y / u n f o r t u n a t e l y , f a i l e d t o r e v e a l c l e a r l y the f o r m a t i o n o f the weakening i n t e r f a c e l a y e r s p o s t u l a t e d above. was  Also, there  no p o s i t i v e evidence i n the m i c r o s t r u c t u r e o f p a r t i a l l y deformed o r  f r a c t u r e d w i r e composites operative.  t h a t the shear mechanism had o r had not been  The main b a s i s f o r the p o s t u l a t i o n t h a t i n t e r f a c i a l shear must  have o c c u r r e d i n . t h e s e m a t e r i a l s was y i e l d s t r e s s on specimen  3•  s i z e , as d i s c u s s e d i n the f o l l o w i n g  composite  section.  S i z e Dependence o f Y i e l d S t r e s s The composite  y i e l d s t r e s s v e r s u s specimen  t h e s t e e l w i r e composites c r i t i c a l size  The  ( F i g u r e 9)  diameter curve f o r  shows a d i s t i n c t anomaly w i t h i n a  range.  composites used i n t h i s i n v e s t i g a t i o n were g i v e n one  a n n e a l s a t 680°C subsequent area.  the observed dependence o f  hour  t o each kO p e r cent r e d u c t i o n i n c r o s s s e c t i o n a l  T h i s a n n e a l i n g tended t o f u r t h e r s p h e r o i d i z e and c o a r s e n the c a r b i d e  i n the s t e e l w i r e s ( F i g u r e 6).  A s s o c i a t e d w i t h s p h e r o i d i z a t i o n would be  expected a s l i g h t l o w e r i n g o f the y i e l d decreasing f i b r e diameter  s t r e n g t h o f the f i b r e s w i t h  (increasing t o t a l annealing time).  The  matrix,  on the o t h e r hand, would be expected t o show an i n c r e a s e i n s t r e n g t h w i t h d e c r e a s i n g specimen  diameter due t o a m a t r i x mean f r e e p a t h e f f e c t  t o the major s t r e n g t h e n i n g mechanism proposed f o r the i r o n powder  analogous composites.  - 65, -  Based on o b s e r v a t i o n s r e p o r t e d f o r o t h e r systems, y i e l d s t r e s s i n c r e a s e s N  with  (\  -1/2  The  where  x  f ) = mean f r e e  path.  f i b r e s t r e n g t h c u r v e , i t i s suggested,  s h e a r i n g a t the m a t r i x r f i b r e i n t e r f a c e .  i s i n t e r r u p t e d by  The m a t r i x c a r r i e s t h e  entire  l o a d on t h e composite once s h e a r i n g o f the i n t e r f a c e i s complete.  However,  r e l a t i v e l y h i g h s t r e s s e s (approaching the t r u e f r a c t u r e s t r e s s of the .  .  i  .  m a t r i x a l l o y ) can be c a r r i e d s i n c e n e c k i n g o f the m a t r i x i s r e s t r a i n e d by the f i b r e s , i . e . t h e r e i s a h y d r o s t a t i c p r e s s u r e e f f e c t . i n , t h e 'matrix. Superimposing the above e f f e c t s g i v e s the schematic  summation, curve  shown i n F i g u r e 2 7 , . which i s o f the g e n e r a l form o f the experimental, y i e l d s t r e s s . c u r v e o b t a i n e d f o r w i r e composites ( F i g u r e D.  9)•  E f f e c t o f Heat Treatment on S a t u r a t e d Powder Composites The  s t r e n g t h s observed  i n powder composites a f t e r s a t u r a t i n g the  i r o n f i b r e s w i t h copper a t 1020°C were extremely dependent on c o o l i n g r a t e from 1020°C.  C o n s i d e r a t i o n of the p o s s i b l e phase t r a n s f o r m a t i o n s i n v o l v e d  became n e c e s s a r y  i n o r d e r t o e x p l a i n t h i s b e h a v i o u r and t o e x p l a i n the  r e l a t i v e l y high strengths obtainable i n saturated  The  composites.  s o l u b i l i t y o f copper i n o<.-iron a t 1020°C has been r e p o r t e d  . 1 7 a t 7-8  p e r cent by weight^Krantz  has  shown t h a t s a t u r a t i o n o f -100  p a r t i c l e s of i r o n w i t h copper w i l l occur a t 1100°C i n a p p r o x i m a t e l y Thus, powder composites which were s o l u t i o n . t r e a t e d i n the p r e s e n t as d e s c r i b e d p r e v i o u s l y , i n v o l v e d .copper^saturated i r o n  +150  mesh  200 minutes. studies  fibres.  P r e v i o u s r e p o r t e d studies, o f n o n - e q u i l i b r i u m phase t r a n s f o r m a t i o n s i n t h e i r o n - c o p p e r system have been l a r g e l y confined: t o a l l o y s c o n t a i n i n g up t o k weight p e r c e n t copper.  I t i s r e c o g n i z e d t h a t these a l l o y s can  be  32  /  /\  matrix shears from fibres  / / /  specimen diameter  *~  .. ON  1  Figure 2 /  S p e c i m e n Diameter  Vs. P r e d i c t e d  Matrix a n d F i b r e  Strengths  ON  -  67 -  s o l u t i o n t r e a t e d and quenched from above or below t h e e u t e c t o i d temperature, 20 then p r e c i p i t a t i o n - h a r d e n e d a t a few hundred degrees C e n t i g r a d e no s t u d i e s have been r e p o r t e d i n the l i t e r a t u r e o f t h e decomposition  However,  non-equilibrium  o f t h e e u t e c t o i d a t 4 weight p e r cent copper.  t h e r e i s no r e f e r e n c e t o a m a r t e n s i t e  .  Specifically,  t r a n s f o r m a t i o n in, t h i s system i n the  26 e x t e n s i v e s t u d i e s o f such t r a n s f o r m a t i o n s by Zackay e t a l Christian  or B i l b y  and  28 25 White  performed some u n p u b l i s h e d work on i r o n  copper, a l l o y s p r e p a r e d  by m e l t i n g and  t o o b t a i n s t r i p m a t e r i a l which was  casting.  He  - 6 weight p e r  hot and c o l d r o l l e d  cut i n t o shaped t e n s i l e specimens.  ingots These  were homogenized ( s o l u t i o n t r e a t e d ) a t 1100°C, c o o l e d a t v a r i o u s r a t e s t o 20°C, and t e s t e d i n t e n s i o n w i t h the f o l l o w i n g r e s u l t s : 1. Water Quenched From 1100°C  Y.S. lbs/in  U.T.S. lbs/in 2  109,ooo 107,000 2.  Elong.  i  2  6.0 6.0  n.a.  1100,000  " A i r c o o l e d " From  C B  5 90  1100°C  U.T.S. lbs/in  Y.S. lbs/in  153,000 151,000 156,000  143,000 l4l,000 146,000  2  Hardness Rockwell  Elong, 2  *  4.0 4.0 5.0  Hardness Rockwell  c 31 c 31 c 32  cent  -68 -  3.  Furnace C o o l e d From: 1100°C  Y.S. lbs/in  U.T.S. lbs/in 2  72,000 76,700 72,500  Elong 2  Hardness Rockwell  •*  61,600 64,800 61,600  B 66 B 67 B 65  15 •16 18  White a l s o examined t h e e f f e c t o f r e h e a t i n g a i r c o o l e d  specimens  f o r 1 hour a t v a r i o u s t e m p e r a t u r e s , f o l l o w e d by a i r c o o l i n g t o 20°C.  .4.  5.  " A i r c o o l e d " From 1100°C,. Reheated t o 400°C f o r 1 hour.  Y.S. lbs/in  130,000 127,000 135,000  119,000 117,000 123,000  2  •*  10 10 7  " A i r c o o l e d " From 1100°C, Reheated t o 600°C f o r 1 hour.  U.T.S. lbs/in  Y-.S. Ibs/in2  Elong  89,000 91,000 95,000  80,000 84,000 86,000  13 13 13  2  6.  Elong  U.T.S. Ibs/in2  *'  . " A i r c o o l e d " From 1100°C, Reheated t o 750°C f o r 1. hour.  U.T.S. lbs/in  84,000 85,000 80,000  2  Y.S. lbs/mn  Elong. 2  74,000 79,000 72,000  ••*  •  16 16 15  These r e s u l t s b e a r a c l e a r r e l a t i o n s h i p t o t h o s e o b t a i n e d i n t h e p r e s e n t s t u d i e s by h e a t - t r e a t i n g powder composites.  I n view o f t h e known  and r a t h e r s m a l l e f f e c t s o f age-hardening the o& s o l i d s o l u t i o n i n Fe-Cu, the  enormous d i f f e r e n c e between the a i r - c o o l e d and f u r n a c e - c o o l e d 6-8$  Cu  a l l o y s cannot be e x p l a i n e d i n such terms. • I n - f a c t , c o n s i s t e n t w i t h t h e phase diagram f o r Fe-Cu, i t i s d i f f i c u l t aircooled  ( o r even quenched) m a t e r i a l s by o t h e r t h a n a m a r t e n s i t e t r a n s -  formation. •to  t o e x p l a i n the h i g h s t r e n g t h o f  I t remains t o e x p l a i n why, the p r o p e r t i e s o f t h e s e a l l o y s  respond  c o o l i n g r a t e i n t h e manner observed.  There a r e s e v e r a l known m a r t e n s i t e t r a n s f o r m a t i o n s i n c l u d i n g  07  26 Cu-Al  and F e - N i  dependent  1  i n which the M  on s l i g h t v a r i a t i o n s i n t h e c o n c e n t r a t i o n s o f t h e minor  components.  Of p a r t i c u l a r i n t e r e s t  i n A l c o n c e n t r a t i o n o f from 11 , 2 6 •M -by a p p r o x i m a t e l y 450 C s  the  and Mf temperatures a r e s t r o n g l y  g  .  i s the C u ^ A l system where a change  t o 15$  ( h y p e r e u t e c t o i d range) lowers t h e  I t i s f e l t that a s i m i l a r e f f e c t occurs i n  Fe-Cu system, w i t h i n c r e a s i n g copper c o n t e n t s l o w e r i n g . t h e For  M. g  purposes o f d i s c u s s i o n , c o n s i d e r t h e quenching o f a homo-  geneous Fe-7$ Cu a l l o y from 1020°C.  Quenching  a t a r a t e greater than  some c e r t a i n c r i t i c a l v a l u e would allow, v i r t u a l l y f u l l r e t e n t i o n o f the copper i n s o l u t i o n . the  v a l u e o f the M  concentration.  s  The h i g h copper c o n c e n t r a t i o n , however, w i l l  and Mf from t h o s e which would e x i s t a t a lower copper  Thus, t h e amount o f m a r t e n s i t e t h a t would be formed a t a  p a r t i c u l a r temperature between M  s  and Mf f o r the 7$ copper a l l o y would  l e s s t h a n t h a t r e s u l t i n g from quenching t o t h e same temperature an of  depress  lower copper c o n c e n t r a t i o n .  be  alloy  Compare t h i s r e s u l t w i t h t h a t p r e d i c t e d  f r o m c o o l i n g the same a l l o y a t a lower r a t e  (i.e.  below the c r i t i c a l  rate).  -70.  -  T h i s would a l l o w . p a r t i a l p r e c i p i t a t i o n o f t h e e p s i l o n phase d u r i n g cooling. solid  I n t h i s manner, t h e copper content  t h a t would be r e t a i n e d i n  s o l u t i o n on f u r t h e r c o o l i n g would be somewhat reduced and t h e  residual X  would have a higher" M  g  and M|.,  a s u b s t a n t i a l l y g r e a t e r amount o f m a r t e n s i t e  The n e t consequence i s t h a t would r e s u l t  on f u r t h e r  c o o l i n g t o t h e r e f e r e n c e temperature, p r o v i d e d t h e r a t e o f c o o l i n g was  r a p i d enough i n t h i s range o f temperature.  F i g u r e - 2 8 shows a suggested c o o l i n g - t r a n s f o r m a t i o n diagram f o r the  iron~7$  argument.,,  copper a l l o y , t h e form-of which i s c o n s i s t e n t w i t h t h e above and. t h e use o f which p e r m i t s  observations  i n the present  i n v e s t i g a t i o n t o be e x p l a i n e d .  It  i s i n t e r e s t i n g t o note t h a t i n t h e C u - A l . s y s t e m  martensite 28  transformations  are reported only f o r hypereutectoid  compositions  . If  s i m i l a r b e h a v i o u r i s e x h i b i t e d by t h e Fe-Cu system, t h i s c o u l d e x p l a i n t h e absence o f p r e v i o u s  observations  a l l e a r l i e r work w i t h t h i s k weight p e r cent  o f a martensite  r e a c t i o n , since nearly  system has been w i t h a l l o y s o f l e s s  than  copper.  Some o f t h e s a t u r a t e d powder composites s t u d i e d i n t h e p r e s e n t work were quenched i n l i q u i d n i t r o g e n from t h e s o l u t i o n treatment tempe r a t u r e and.then t e s t e d - i n t e n s i o n a t room temperature. mechanism t o e x p l a i n the. r e s u l t s o b t a i n e d , , t h e would be r e q u i r e d t o be c o m p l e t e l y  martensite  F o r t h e above transformation  r e v e r s i b l e , a.condition.that exists i n  most o t h e r systems which e x h i b i t m a r t e n s i t i c type  transformations ^. 2  I n t h e powder composites t h e r a t e o f c o o l i n g due t o " a i r c o o l i n g " i s apparently  such as;, t o produce t h e maximum amount o f m a r t e n s i t i c phase  c o n s i s t e n t w i t h t h e proposed- t r a n s f o r m a t i o n .  Reheating o f " a i r c o o l e d "  -11>  Time  Figure 28  Cooling Rate -Transformation Diagram For an Iron7 % Copper Alloy  -  - 72 specimens a t kOO°C  f o r one hour i s presumed t o have p a r t i a l l y  the m a r t e n s i t e , whereas a one hour treatment a t rJ c^Q°C t r a n s f o r m e d t h e m e t a s t a b l e m a r t e n s i t i c phase  -  tempered  has a p p a r e n t l y  i n t o a r e l a t i v e l y coarse ,  m i x t u r e o f low-copper <oC and t h e e p s i l o n phase..- The l a t t e r t r a n s f o r m a t i o n would be expected t o a l l o w a . r e t u r n o f heterogeneous y i e l d i n g i n t h e f e r r i t e , a c o n d i t i o n which was, i n f a c t ,  observed.  An i n t e r e s t i n g r e s u l t o f t h e heat t r e a t m e n t s o f " s a t u r a t e d " composites  (and one which cannot be e x p l a i n e d i n terms o f a simple  m a r t e n s i t i c t r a n s f o r m a t i o n ) i s the apparent-age-hardening  o f specimens  quenched  In studies o f  i n l i q u i d n i t r o g e n a n d h e l d a t room temperature.  precipitation of £  oC  from  i t has been r e v e a l e d t h a t maximum hardness  o c c u r s as a r e s u l t o r a g e i n g a t temperatures between kOO and "JQ0°C. In a d d i t i o n , measureable  p r e c i p i t a t i o n o f oC  from  £  20  occurs only a t 19  temperatures above 600°C and then o n l y t o a v e r y l i m i t e d e x t e n t it  .  Thus  i s apparent t h a t t h e normal p r e c i p i t a t i o n phenomenon g e n e r a l l y observed  i n t h e Fe-Cu system does n o t a p p l y i n t h i s c a s e . I t i s p o s s i b l e t h a t some tempering o f t h e h i g h copper m a r t e n s i t e formed by auenching t h e s a t u r a t e d  (7-8$ copper) )£ o c c u r s a t 20°C i n view  o f the h i g h degree o f s u p e r s a t u r a t i o n i n v o l v e d . retained V  may o c c u r .  A l s o , p r e c i p i t a t i o n from  T h i s c o u l d i n t u r n cause h a r d e n i n g o f t h e e x i s t i n g  m a r t e n s i t e by t h e f o r m a t i o n o f coherency s t r a i n s , and/or r e s u l t i n t h e c o n v e r s i o n o f some r e t a i n e d  ¥  t o lower-copper m a r t e n s i t e .  Of p a r t i c u l a r i n t e r e s t i s F i g u r e 2 6 , which shows t h e v a r i a t i o n of t h e y i e l d s t r e s s o f t h e composites w i t h changes t h e s a t u r a t i o n temperature.  i n c o o l i n g r a t e from  I t i s apparent t h a t the maximum s t r e n g t h s i n  the composites o c c u r a s a r e s u l t  o f c o o l i n g r a t e s o f between 20 and P j C C / s e c .  The  curve a l s o shows v i r t u a l l y a l i n e a r dependence o f y i e l d s t r e s s w i t h  v a r i a t i o n s i n c o o l i n g r a t e s l e s s than the v a l u e s j u s t mentioned.  This  i s c o n s i s t e n t w i t h what would would he expected from a c o n s i d e r a t i o n o f the c o o l i n g - t e m p e r a t u r e curve shown i n F i g u r e 2 8 .  Slower c o o l i n g r a t e s  would a l l o w d i f f u s i o n - c o n t r o l l e d phase t r a n s f o r m a t i o n s t o o c c u r d u r i n g c o o l i n g w i t h a subsequent  E.  Deformation  softening effect.  Behaviour- o f M e t a l F i b r e R e i n f o r c e d M e t a l s 17  Krantz  1  has examined the p r o p e r t i e s i n the b u l k form.of a  c o p p e r - i r o n a l l o y e s s e n t i a l l y i d e n t i c a l t o the m a t r i x a l l o y i n these composites.  fibre  He found, the u l t i m a t e t e n s i l e s t r e n g t h t o be 4 7 , 0 0 0 p s i w i t h  an e l o n g a t i o n t o f r a c t u r e o f 3 0  p e r cent i n 1 i n c h .  - The t r u e f r a c t u r e  stress  however, can be t a k e n as a p p r o x i m a t e l y 118,000 p s i on the b a s i s o f a r e a a t the  fracture. The  s a t u r a t e d and h e a t - t r e a t e d powder composites  p r o v i d e d an  e x c e l l e n t o p p o r t u n i t y t o examine the e f f e c t o f the r e l a t i v e s t r e n g t h s o f f i b r e and m a t r i x on composite  properties.  the y i e l d and u l t i m a t e s t r e n g t h s were low and the e l o n g a t i o n t o f r a c t u r e was in.fact  Thus i n f u r n a c e - c o o l e d m a t e r i a l , and  (39,000  high ( 2 7  5^,000  p s i respectively)  p e r c e n t ) . - These p r o p e r t i e s are  s i m i l a r t o those o f u n s a t u r a t e d composites  of s i m i l a r s i z e .  Clearly,  i n t h i s case, d e f o r m a t i o n o f the m a t r i x i s n o t b e i n g r e s t r i c t e d a p p r e c i a b l y by t h e f i b r e s ,  since the l a t t e r are f e r r i t e  (Q£)  o f low d i s s o l v e d  copper  c o n t e n t w i t h d e f o r m a t i o n b e h a v i o u r s i m i l a r t o t h a t o f the m a t r i x . By c o n t r a s t , a i r c o o l e d composites  c o n t a i n e d f i b r e s f o r which the  y i e l d and u l t i m a t e s t r e n g t h s c o u l d be expected t o be a t l e a s t 142,000 and 152,000  p s i r e s p e c t i v e l y a c c o r d i n g t o White's r e s u l t s . . The  composites  fact that  e x h i b i t e d s t r e n g t h s o f 110,000 p s i ( y i e l d ) and 140,000 p s i  such  • - Ik  ( u l t i m a t e ) can be accounted than i n the f i b r e s .  f o r by a " s i z e e f f e c t " i n the m a t r i x r a t h e r  The h i g h - s t r e n g t h f i b r e s c o n s t i t u t e s t r o n g b a r r i e r s  t o flow i n the m a t r i x . stages o f p l a s t i c  That i s , d i s l o c a t i o n p i l e - u p i n the v e r y e a r l y  s t r a i n i n the m a t r i x  ( p r i o r t o the a t t a i n m e n t  reported y i e l d s t r e s s ) leads t o very rapid.matrix hardening. t h a t the l e n g t h of p i l e > u p s  of the  The  i s s e v e r e l y r e s t r i c t e d a t the s m a l l  and. f i b r e diameters  i n v o l v e d , . means t h a t t h e ' m a t r i x s i z e e f f e c t "  realised i a large.  The m a t r i x a c c o r d i n g l y can support  fact composite being  s t r e s s e s much  h i g h e r than i t s b u l k u l t i m a t e s t r e n g t h , perhaps a p p r o a c h i n g fracture  -  i t s true  stress.  - S i m i l a r arguments p r o v i d e an e x p l a n a t i o n . f o r the s t r e n g t h p r o p e r t i e s o f composites  w i t h o t h e r t h e r m a l h i s t o r i e s i n the p r e s e n t work.  It  remains,  however, t o compare the t h e o r i e s advanced by p r e v i o u s i n v e s t i g a t o r s w i t h the arguments proposed  above. 5  The  " f i b r e s i z e e f f e c t " r e p o r t e d by J e c h e t a l .  r e i n f o r c e d copper  i n tungsten  fibre-  can probably, be p a r t l y a t t r i b u t e d t o the m a t r i x s i z e  effect  discussed previously. On the b a s i s o f s e v e r a l assumptions, d i c t e d v a r i a t i o n of composite developed  an e x p r e s s i o n f o r ' t h e p r e -  s t r e n g t h w i t h m a t r i x mean f r e e p a t h can  be  mathematically.  Assuming t h a t the f i b r e s i n the composite t h e u n i f o r m l y packed a r r a y shown i n F i g u r e 2 9 , can be r e l a t e d t o the t o t a l composite  a r e continuous and  t h e n the a r e a o f a  a r e a as f o l l o w s :  fibre  have  -7,5-  Figure 29.  Assumed F i b r e  Distribution  -  . 76 -  T o t a l a r e a o f t r i a n g l e i n F i g u r e 29  A  1 2  =  t  S  S  f  2  Area o f f i b r e i n s i d e  • A  =  F  i  2 f  k  triangle  / f  2 ^  Thus, t h e i n t e r f i b r e  S  d  2  ^t  S  =  t  Tt  TT  =  Tf CLT  "8"  Volume F r a c t i o n F i b r e s =  S 2 f  N, f  s p a c i n g (S^.) i s :  f  2 j  N  f  A l s o , s i n c e t h e r e i s a l i n e a r r e l a t i o n s h i p between  interfibre  s p a c i n g and m a t r i x mean f r e e p a t h f o r t h e case o f c o n t i n u o u s f i b r e s ,  .M.F-.P.  c*  . d  then:  f  YN"f Gensamer,. working  w i t h s t e e l s , has shown.that t h e s t r e n g t h o f a  m a t r i x c o n t a i n i n g a hard d i s p e r s e d phase i s p r o p o r t i o n a l t o t h e l o g o f r e c i p r o c a l mean f r e e p a t h .  Other  -1/2  systems have found a . (M.F.P.)  i n v e s t i g a t o r s , w i t h v a r i o u s two-phase dependence o f s t r e n g t h .  both these f u n c t i o n s a r e q u i t e s i m i l a r .  M a t h e m a t i c aJl l y ,  T h e r e f o r e , assuming a .(M.F.P.)  -1/2  relationship,  strength o f matrix  (^ V )  -1/2 o<  (M.F.P.)  o<  N °" f  d  2 5  .....(7)  f  I t now becomes n e c e s s a r y t o modify t h e t h e o r y o f combined which assumes t h a t t h e m a t r i x s t r e n g t h SJ~  m  i s independent  action,  o f the volume  -77 -  fraction  or diameter  XT  o f the f i b r e s p r e s e n t , i . e .  =  A  ST  f  f  .+  A  T  f f i  • C o n s i d e r the e f f e c t o f i n c r e a s i n g . t h e volume f r a c t i o n o f the fibres  (i.e.  A^) w h i l e k e e p i n g d^ c o n s t a n t .  T h i s w i l l decrease the  v a l u e o f A ,. t h e volume f r a c t i o n o f t h e m a t r i x .  The t h e o r y o f combined  m  a c t i o n i n d i c a t e s t h a t t h e composite  strength increase i s l i n e a r , i . e .  t h e r e i s no accompanying change i n . the v a l u e s . o f t h e . f i b r e and m a t r i x stresses.  The t h e o r y proposed.however, i s t h a t t h e matrix, s t r e n g t h  i s p r o p o r t i o n a l t o (volume f r a c t i o n o f f i b r e s ) ' 0  2 5  and, thus any- i n c r e a s e  i n . t h e volume f r a c t i o n o f f i b r e s causes an i n c r e a s e i n . t h e s t r e n g t h o f t h e m a t r i x . - The e f f e c t , a l t h o u g h ' r e l a t i v e l y s m a l l , has maximum i n f l u e n c e a t low volume f r a c t i o n s . o f f i b r e s p o s s i b l y account  ( i . e . . l e s s than 2 0 % ) ;  This could  f o r t h e d i s c r e p a n c y between t h e e x p e r i m e n t a l p o i n t s and 8  the c a l c u l a t e d s t r a i g h t l i n e observed by McDanels e t a l . p l o t s o f composite  I n t h e i r work,  u l t i m a t e t e n s i l e s t r e s s v e r s u s volume p e r cent  f o r t h r e e s e p a r a t e f i b r e diameters  fibres  gave e x p e r i m e n t a l v a l u e s a t low volume  p e r cent f i b r e s t h a t were g r e a t e r than t h e v a l u e s c a l c u l a t e d , from t h e t h e o r y o f combined a c t i o n . Equation.(7)  i n d i c a t e s an i n v e r s e square  m a t r i x s t r e n g t h w i t h f i b r e diameter. the diameter  of the f i b r e .  e v i d e n c e t o support t h i s  The e f f e c t  r o o t dependence o f  i s g r e a t e r , the s m a l l e r  U n f o r t u n a t e l y , t h e r e i s no d i r e c t  experimental  premise.  I t i s thus p r o p o s e d . t h a t  the e x i s t i n g t h e o r y ' f o r p r e d i c t i n g the  s t r e n g t h o f f i b r e - r e i n f o r c e d composites  s h o u l d be m o d i f i e d . t o become:  ^  =  A  f ^ " f  +  \  ^m  +  V  K  d  (8)  f  where K i s a c o n s t a n t depending on t h e r e l a t i v e s t r e n g t h s ' o f t h e f i b r e and.the m a t r i x .  A v a l u e o f K c a n be c a l c u l a t e d from one s e t o f r e s u l t s  obtained  i n t h i s i n v e s t i g a t i o n , namely, t h e " a i r c o o l i n g " o f t h e c o a r s e i r o n powder composites.  S u b s t i t u t i n g p e r t i n e n t values i n t o equation  gives; K e q u a l t o 2 8 l l b s / i n '  a t a . f i b r e diameter  (8) and s o l v i n g  o f 10 m i c r o n s .  IfK  depends only- on t h e r e l a t i v e s t r e n g t h s o f t h e f i b r e and. t h e matrix, then e q u a t i o n (8) s h o u l d g i v e the composite mesh powder composites A^,, A  m  and d^.  s t r e n g t h f o r t h e " a i r c o o l e d " -325  with a s u b s t i t u t i o n of the corresponding values of  Such a c a l c u l a t i o n g i v e s a v a l u e f o r t h e composite  of 137>600-psi, which i s 13 p e r cent g r e a t e r t h a n t h a t determined mentally  (122,000 p s i ) .  strength.  c a l c u l a t e d v a l u e o f t h e s t r e n g t h i s based  on t h e assumption  t h a t t h e mean f r e e p a t h i s l i n e a r l y dependent on t h e diameter ( i . e . continuous -525  experi-  The t h e o r y o f combined a c t i o n , on t h e other hand,  p r e d i c t s 109,500 p s i . as t h e composite  The  strength  f i b r e s a r e assumed).  mesh powder composites  of the f i b r e  T h i s i s n o t t r u e f o r the case o f  (Figure 23).  A p p a r e n t l y t h e mean f r e e  path  i s s e v e r a l times g r e a t e r than has been assumed i n the mathematical  develop-  ment. - T h i s w i l l have t h e e f f e c t o f l o w e r i n g t h e v a l u e o f t h e t h i r d  term  i n equation ( 8 ) , thus.bringing the c a l c u l a t e d value c l o s e r t o that determined e x p e r i m e n t a l l y . additional effect  On t h e o t h e r hand, i t i s hard t o v i s u a l i z e any  i n c r e a s i n g t h e s t r e n g t h as c a l c u l a t e d from the. t h e o r y  of combined a c t i o n ,  ( a p a r t from i n c r e a s i n g t h e s t r e n g t h o f t h e f i b r e s due  t o a " s i z e e f f e c t " , a c o n d i t i o n w h i c h h a s not been found t o occur investigation).  in.this  - 79 V.  CONCLUSIONS  No s t r e n g t h e n i n g e f f e c t  1.  has been observed i n f i b r e - r e i n f o r c e d  composites i n t h i s work which c a n . b e a t t r i b u t e d t o f i b r e " s i z e  effects".  However, the s t r e n g t h of m e t a l f i b r e r e i n f o r c e d m e t a l composites i s b e l i e v e d t o be g r e a t l y i n f l u e n c e d by a . " s i z e Any. f a c t o r which a f f e c t s  2.  effect"  matrix.  the m a t r i x mean f r e e p a t h ( e . g . volume  f r a c t i o n of f i b r e and f i b r e diameter) strength.  i n the  can be expected t o a f f e c t  .However,. the e x t e n t t o which such e f f e c t s  are important  c o n t r o l l e d by the r e l a t i v e hardness or s t r e n g t h o f - t h e f i b r e ; e f f e c t i v e n e s s as a b a r r i e r t o flow, i n the . 3.  composite is  i . e . by< i t s  matrix.  The f o l l o w i n g m o f i d i c a t i o n of the t h e o r y of combined a c t i o n  is  proposed f o r p r e d i c t i n g the s t r e n g t h of a f i b r e - r e i n f o r c e d . c o m p o s i t e : ^~c  =  A  —  *t  f  +  Ai  —-  ^ m  + 1 +  A  f  A K  d  f  -1/2  where A i s volume f r a c t i o n , f r e f e r s t o f i b r e ,  m refers  to m a t r i x ,  df i s f i b r e diameter and-K i s a c o n s t a n t whose v a l u e depends on the hardness . o f the k.  fibre. •In composites of copper r e i n f o r c e d by s t e e l w i r e s , weakening  o f the m a t r i x - f i b r e i n t e r f a c e t o the i n t e r f a c e .  can o c c u r as a consequence o f carbon  T h i s l e a d s t o s h e a r i n g a t the i n t e r f a c e  segregation  i n the e a r l y  stages  of t e n s i l e deformation. 5.  A l l o y s c o n t a i n i n g 6 t o 8 weight p e r cent copper i n i r o n e x h i b i t  a m a r t e n s i t e t r a n s f o r m a t i o n when c o o l e d from the phase d i a g r a m .  The m a r t e n s i t e  V  r e g i o n of the Fe-Cu  formed at 6 p e r cent copper has an u l t i m a t e  s t r e n g t h of a p p r o x i m a t e l y 1 5 0 , 0 0 0 p s i and e x h i b i t s a p p r e c i a b l e d u c t i l i t y . This martensite  t r a n s f o r m a t i o n a p p a r e n t l y has not been observed h e r e t o f o r e  i n s t u d i e s by o t h e r i n v e s t i g a t o r s  of Fe-Cu a l l o y s .  -  80  -  V I . - SUGGESTED FUTURE WORK  T h i s work has been p r i m a r i l y o f an exploratory, nature  and t h e  r e s u l t s have suggested d i r e c t i o n s o f f u t u r e work which might be p r o f i t a b l y explored.  I t i s recommended: t h a t f u r t h e r s t u d i e s be c a r r i e d out-on. t h e phase.transformations  Experimental  i n h y p e r e u t e c t o i d Fe-Cu a l l o y s o f b u l k  v e r i f i c a t i o n o f the proposed r u l e f o r p r e d i c t i n g  composite s t r e n g t h i s recommended. of experimental  form.  T h i s c o u l d be done by t h e e x t e n s i o n  work t o o t h e r systems and by means o f experiments i n which  t h e f i b r e s i z e , d^, i s v a r i e d - w i t h o u t  varying the inherent f i b r e  strength.  In a d d i t i o n , i t i s f e l t t h a t t h i s work c o u l d be extended t o even s m a l l e r f i b r e s i z e s and/or s m a l l e r m a t r i x mean f r e e p a t h  distances  by a j u d i c i o u s c h o i c e o f w i r e drawing equipment, powder s i z e s , and heat treating conditions.  S a t u r a t i o n o f t h e f i b r e s w i t h copper p r i o r t o f i n a l  drawing c o u l d h e l p t o o b t a i n t h e d e s i r e d r e s u l t .  - 81 VII.  BIBLIOGRAPHY  1,  Coleman, B.D., J . Mech and Phys. o f S o l i d s , 7,  2.  P a r r a t t , N. J . , Rubber and P l a s t i c  .3.  D i e t z , A. G. H., "Design Theory Reinforced P l a s t i c s ,  60 (I958).  Age, 4 l ( 3 ) , 263  (I960).  of Reinforced P l a s t i c s " ,  Fiberglass.  Chapter 9 , R e i n h o l d , New York, N.Y., (1954). S o c i e t y , A p r i l I.962, 593.  k.  S u t t o n , W. H., J . Amer. Rocket  5.  J e c h , R. W., McDanels, D. L., and Weeton, J . W., "Composite M a t e r i a l s and Composite S t r u c t u r e s " , P r o c . S i x t h Sagamore Ordnance M a t e r i a l s C o n f e r e n c e , August 1959, 116.  6.  K e l l y , A., P r i v a t e  7.  C r a t c h l e y , D., Powder Met., (11),  8.  McDanels, D. L., J e c h , R. W., Weeton, J . W., T e c h n i c a l Note D - l 8 8 l ,  communication. 59 ( I 9 6 3 ) .  N.A.S.A., Washington D.C., October 9.  1963.  Dow, N.F., T e c h n i c a l I n f o r m a t i o n S e r i e s , R 63SD6I, G e n e r a l (I96I).  Space S c i e n c e s L a b o r a t o r y , 10..  Koppenaal,  11.  S u t t o n , W. H., Rep. No. R  A . , P a r i k h , N., T r a n s . A.I.M.E., 224, I I 7 3  12.  Whitehurst,  6  2  H. B., Michener,  S  D  6  Electric,  5  Class  (I963).  1, G e n e r a l E l e c t r i c ,  (I962).  J . W., Lockwood, P., Proc. S i x t h Sagamore  Ordnance M a t e r i a l s C o n f e r e n c e , August 1959, 248. 13.  C r a t c h l e y , D., Heywood, D. M., t o be p u b l i s h e d .  14.  Wagner, H . J . , B a t t e l l e T e c h n i c a l Review, 12 (12)  15.  S u t t o n , W. H., Chorne, J . , M e t a l s E n g i n e e r i n g Q u a r t e r l y , 3 ( 1 ) , 1963.  16.  R o b e r t s , D. A., Memorandum 80, Defence M e t a l s I n f o r m a t i o n C e n t e r ,  17.  January 1 9 6 I . K r a n t z , T., P r i v a t e communication based of B r i t i s h Columbia.  18.  W r i e d t , H. A., Darken, L. S., T r a n s . A.I.M.E. 218,  19.  Newkirk, J . B., T r a n s . A.I.M.E. 209, 1214 (1957).  20.  Hornbogen, E . , Glenn, R.C., T r a n s . A.I.M.E., 218, 1064  8 (1963).  on M.A.Sc. p r o j e c t ,  University  (i960).  (i960).  82  -  Bibliography Continued....  21.  B e n d i , A . , Chem.. Rev.  ^2, 4 1 7 ( 1 9 5 5 ) . "  22.  S n o w b a l l , R . F . , • M . A . S c . T h e s i s , U n i v e r s i t y of B r i t i s h C o l u m b i a ,  23.  Gensamer,  M . , P e a r s a l l , , E . B . , • P e l l i n i , , W.S.  Low J r . ,  J.R.,  1961.  Trans „  , A . S . M . 30, 983 (1942). 24.  B r e d z , . N . , S c h w a r t z b a r t , H . , Welding Research Supp. 4 l ,  25.  White,  26.  Zackay, V . F . , J u s t u s s o n , M . W . , Schmatz, D . J . , " S t r e n g t h e n i n g Mechanisms i n S o l i d s " , - S t r e n g t h e n i n g by M a r t e n s i t i c T r a n s f o r m a t i o n s , Chapter J,A . S . M . (I960)-. •  129-S  H . , U n p u b l i s h e d work, U n i v e r s i t y o f B r i t i s h C o l u m b i a ,  (1962). 1965.  :  27.  Kaufman,• L . Cohen, M . , " T h e Mechanism of Phase T r a n s f o r m a t i o n s i n Metals", Nucleation i n Martensitic Transformations, I n s t i t u t e M e t a l s , London, (I956) I87.. . -  28.  Bilby, B.A.,, Christian, J.W.,  Ibid.  29.  Troiano, A . R . , 'Greninger, A . B . , A . S . M .  121. Handbook  (1948) 263.  of  V I I I . APPENDICES APPENDIX I . . Iron-Copper System  950  -OANILOFF DIAGRAM -WRIEDT AND DARKEN"  1  900 O  850  a. z>800 < cr  UJ  a. s  Ul  750  700  650  3  I 2 , 4 WEIGHT PERCENT COPPER  F e - r i c h End Reproduced from W r i e d t and Darken, T r a n s . A.I.M.E., 218,  Reproduced from B u t t s ,  (i960)  C u - r i c h End "Copper, t h e M e t a l , I t s A l l o y s and Compounds New York, U7I ( 1 9 5 4 ) .  - 84 •APPENDIX I I . A.  Data f o r S t e e l W i r e - R e i n f o r c e d Composites  Composite Number  W-l-A  W-2-A  W-3-A  Specimen Diameter (in)  Y.S. Matrix psi  Y.S. Composite psi  O.O75 O.O67 0.052 0.051 0.047 0.047 0.043 O.O38 0.034  5,800 8,600 10,500 18,200 '21,500 26,100 16,800 23,600 18,200 19,500 24,000  0.057 0.047 0.047 0.047  15,000 18,700 16,800 15,900  21,600 26,500' •31,300 35,100 34,300 32,000 38,300 •39,200 •34,000 36,300 .45,400 42,700 53,800 31,900 34,500  0.070 0.063 0.060  14,500 12,300 13,900 18,300 15,200 14,000 21,400 •25,500 24,500 31,400 4o,ooo .45,200  34,400 39,200 .41,300 38,600. 35,300 32,000 .33,000 33,500 36,300 35,400 •44,100 ,50,800  O.O98 O.O89  •O.O58 0.053 0.051 0.042 0.040 0.036 0.036 0.032 0.022  :  U.T.S, psi  47,200 48,700 68,500 63,100 54,400 53,700 53,400 54,700 61,700 64,500 74,500 49,600 42,8oo •37,800 42,600 63,400 68,600 66,400 56,100 52,50048,100 46,400 4o,000 44,200 54,800 74,700 71,200  Disc. Y i e l d Unit Strain (in) 0  0  0  0  .  0  2  3  0.040 0  .  0  3  6  0  .  0  6  3  0  .  0  6  3  0.047 O0O34 0  .  0  2  8  0  .  0  4  6  0  .  0  5  0  n.a. 0  .  0  4  3  0  .  0  3  9  0  .  0  3  5  0  .  0  3  0  0  .  0  3  8  0  .  0  3  5  0  .  0  4  6  7  0  .  0  1  0  .  0  3  0  0  .  0  2  7  0  .  0  1  8  0  .  0  0  0  0  .  0  2  0  •Appendix II„ C o n t i n u e d . B. •Data f o r I r o n Powder Composites  Composite • Number  Powder 2  Specimen Diameter (in)  O.O96 O.076  ,  2 2  9 8  , ,  7 5  0 0  0  •Disc. Yield-Elong.  '(%•) ,.,1  .1,41,100 45,600. 45,700  0  0 ' 0 0.1 •••  57,200  0.057  33,600  42,200  29,100  44,800  0 . 0 5 0  33,000  0.027  49,400  ,4.2  3  48,800  4.1  33,100  46,800  3  45,800  -2..1 •. 0  0 . 0 7 7  0.074 0.071 0.069 0.063 0.059 0.051 0.046  o.o4o 0.038 0.034 0.028 0.025  ft  .  .U-.T-.S. psi  0.073 0.061  o.o46  Powder 3  Composite Yield- Stress psi  2  9  3  2  ,  ,  ,  4  5  9  0  0  0  40,000  0  0  0  2  8  ,  7  0  0  2  9  ,  8  0  0  27,900 26,200 34,000 30,600 .38,000 33,200 ' 33,000  34,700 34,700  42,400  42,600 .45,400 ^  3  ,  5  0  0  ft •ft  ft  ft  -1.4  1.8 0.8  39,960 43,500 ,47,500  ,1.0  .41,800  3,0  45,600 :42,300 4l,600  2.9  3.2  2.5  -ft  ft  D i s c o n t i n u o u s Y i e l d i n g was p r e s e n t but range over which i t a c t e d c o u l d not be c l e a r l y d e f i n e d .  

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