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UBC Theses and Dissertations

A study of infiltration in metallic systems. Parkinson, Frederick Lloyd 1964

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A STUDY OF INFILTRATION IN METALLIC SYSTEMS  by  FREDERICK LLOYD PARKINSON  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 standard  t h e s i s as  conforming to  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 of the Department  of Metallurgy  THE UNIVERSITY OF BRITISH COLUMBIA April,  1964  In p r e s e n t i n g t h i s t h e s i s the requirements British  Columbia,  f o r an advanced degree  at the U n i v e r s i t y of  I agree t h a t the L i b r a r y s h a l l make i t  a v a i l a b l e f o r reference f o r extensive  in p a r t i a l fulfilment of  and s t u d y .  I f u r t h e r agree t h a t p e r m i s s i o n  c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be  g r a n t e d by the Head o f my Department o r by h i s It  freely  representatives.  i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s  for  f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n .  Department o f  Metallurgy  The U n i v e r s i t y o f B r i t i s h Columbia, Vancouver 8, Canada. Date  A p r i l 20.  1964  ii ABSTRACT  Porous s k e l e t o n s p r e p a r e d by s i n t e r i n g l o o s e m e t a l powders have been i n f i l t r a t e d with l i q u i d  The systems copper,  iron-copper,  metals.  i n v e s t i g a t e d were n i c k e l - l e a d , n i c k e l - s i l v e r , i r o n - s i l v e r and i r o n - s i l v e r / c o p p e r .  nickel-  Contact angle  periments- f o r the above systems were a l s o performed u s i n g the s e s s i l e  ex-  drop  technique. -  I t was f o u n d t h a t the r e s u l t a n t  d e n s i t y o f the i n f i l t r a t e d  composite  depends d i r e c t l y upon the amount of p r e v i o u s d e o x i d a t i o n of the s k e l e t o n and a l s o the  shrinkage p o r o s i t y which r e s u l t s  infiltrant.  from s o l i d i f i c a t i o n of the molten  I t was f o u n d t h a t the thermodynamic d r i v i n g f o r c e f o r i n f i l t r a -  t i o n i s the p r o d u c t  ~S  In the systems  Ly-cos © where  73gy  Ti'^ycos 9 =  - "^SL*  i n which i n f i l t r a t i o n o c c u r r e d the c o n t a c t angle was  l e s s than 28° u s u a l l y b e i n g much lower b u t not z e r o . where the c o n t a c t angle i s 36°,  In s i l v e r - i r o n system  i n f i l t r a t i o n d i d not o c c u r a t a l l .  The i n -  f i l t r a t i o n o f s i l v e r - c o p p e r a l l o y s i n t o an i r o n s k e l e t o n was more f a v o u r a b l e as the copper content that  I_iV  was i n c r e a s e d .  cos 9 i n c r e a s e s  T h i s was shown t o be due t o the  as the copper c o n c e n t r a t i o n  fact  increases.  In o r d e r to determine the r a t e of i n f i l t r a t i o n experiments  were  per-  formed whereby the drop i n h e i g h t o f a molten column of i n f i l t r a n t as a result  of i n f i l t r a t i o n was measured w i t h movie camera.  v e r y r a p i d as porous s k e l e t o n s in less to the  than 0.3  sec.  of the order of 5  c m  i  n  I n f i l t r a t i o n was l e n g t h were  infiltrated  The h e i g h t o f i n f i l t r a t i o n was f o u n d t o be p r o p o r t i o n a l  square r o o t of time and the r a t e o f i n f i l t r a t i o n ,  r a p i d l y w i t h time o f i n f i l t r a t i o n .  d h/  dt,  decreased  vii ACKNOWLEDGEMENT The author i s grateful f o r the advice and encouragement given by his research d i r e c t o r , Dr. J . A. Lund.  Thanks are also extended to  other faculty members and fellow graduate students f o r many helpful discussions.  F i n a n c i a l assistance i n the form of Defence Research Board Grants No. 7501-02 and No. 7501-03 i s g r a t e f u l l y  acknowledged.  iii TABLE OF CONTENTS Page A.  B.  1.  Wettability  2. 3. h. 5» 6. 7. 8.  D r i v i n g Force f o r I n f i l t r a t i o n Surface Films S u r f a c e Roughness • E f f e c t o f Temperature on I n f i l t r a t i o n Rate o f I n f i l t r a t i o n Solubility S o l u t e A d d i t i o n s t o the L i q u i d Phase  1  .  ,  .  k 6 7 8 10 12 13  .  EXPERIMENTAL 1.  2. 3. h. 5. 6. 7. 8.  C.  1  INTRODUCTION  Materials a. Powder b. Infiltrant Skeleton Preparation I n f i l t r a t i o n Procedure Rate Measurement D e n s i t y Measurements Metallography S e s s i l e Drop Experiments Measurement of Contact Angle a. B a s h f o r t h and Adams Technique b. Volume o f Drop Method  lh  • • •  21  RESULTS AND DISCUSSION 1. 2.  3.  h. 5.  I n f i l t r a t i o n Mechanism Rate of I n f i l t r a t i o n a. A n a l y s i s o f E x p e r i m e n t a l Geometry b. Rate E q u a t i o n s • c. Rate o f I n f i l t r a t i o n R e s u l t s • Density • • • a. D e n s i t y G r a d i e n t s Due t o Uneven D e o x i d a t i o n b. S o l i d i f i c a t i o n Porosity c. Copper-Silver I n f i l t r a t i o n i n t o Iron d. E f f e c t of Temperature on R e s u l t a n t D e n s i t y o f P b - N i - . System , • E f f e c t of Temperature on H e i g h t o f C a p i l l a r y R i s e . . . . . Contact Angle . • • a. Ag-Cu A l l o y s on Fe Base Sheet b. Contact angle o f Ag on N i Sheet c. C a l c u l a t i o n o f $*SL • • • • d.  lh lh lh 15 15 16 16 18 19 19 19 20  21 27 27 30 3^ h2 h2 h2 h'J 5h 57 62 62 64 66 67  Secondary D i f f u s i o n •  68  D.  CONCLUSIONS  E.  BIBLIOGRAPHY  69  F.  APPENDICES  71  iv  LIST OP FIGURES 1  Figure  Page  1.  Vector Diagram of Surface Forces  2  2.  I n f i l t r a t i o n Experiment  4  3»  Grain Boundary Grooving  4.  Diagram of Apparatus  17  5>  I n f i l t r a t i o n of Specimen 86 with 30$ Required S i l v e r  23  6.  Specimen 74 Showing Residual Porosity at Regions of High .  . . . . .  7  25  Tortuosity 7»  Geometry of I n f i l t r a t i o n Mold and Porous Skeleton  8.  Height of I n f i l t r a t i o n vs Time f o r S o l i d Nickel Rod "Infiltrated"  with S i l v e r  26  28  1  " I n f i l t r a t i o n " of S o l i d Nickel Rod with S i l v e r  29  10.  Plot of H  ve R  32  11.  F i s t of ^ dt  V B t for R  12.  9.  e  f o r t = 3/24 seconds 2.39, 29.5 and 78.5 x 10"^ em . . .  33  Height of I n f i l t r a t i o n vs t / f o r  -50+100 Nickel and Copper .  3?  13.  Height ©f I n f i l t r a t i o n ve t / f o r  -50+100 Nickel and S i l v e r .  38  14.  Hoight of I n f i l t r a t i o n ve t / f o r -20+35 Nickel and Copper  15*  Plot of t r at Plot of  16.  e e  1  1  1  2  2  2  .  t f o r -50+100 Nickel and S i l v e r vs t f o r  -20+35 Nickel and.Silver  39 40  4l  dt  68 . . . . . . . . . . . . .  I?.  Density vs Distance f o r Specimen  1-8<  Density ve Distance f o r Specimen 66  19.  Percent Reduction i n Skeleton Porosity vs Copper Content i n  20.  Copper-Silver I n f i l t r a n t . . . . . . . . . . Contact Angle vs Copper Content f o r Copper-Silver A l l e y s on Armco Iron Sheet . . .  21. • 22.  Plot of  ?5"LV  COS 9  44 45  51 53  vs Copper content f o r Copper-Silver Alloys  on Armco Iron Sheet . . . . . . . . . . . . . . . . . . . . Density of Lead I n f i l t r a t e d Nickel composites vs Temperature ©f I n f i l t r a t i o n . . . . . . . . . . . . .  55 56  V  L i s t of F i g u r e s Continued Figure  Page  23•  Contact Angle f o r L e a d - N i c k e l System vs Temperature  2k.  Cosine of the C o n t a c t Angle f o r L e a d - N i c k e l System vs Temperature  . . . . . .  .  58  59  25.  H e i g h t o f I n f i l t r a t i o n f o r L e a d - N i c k e l System vs Temperature.  6l  26.  Contact Angle f o r N i c k e l - S i l v e r System vs Time a t 985°C" . . .  65  vi  LIST OF TABLES Table  Page  1.  Sintering Conditions f o r Skeleton Preparations . . .  15  2.  .Density D i s t r i b u t i o n f o r Specimen 74  24  3.  Values of Parameters i n Equation 17  4.  Calculated and Experimental Slope Values of h vs t ^ / ^ Plots  5.  Resultant Density with Non-Uniforn Dsoxidation  43  6.  /O  46  7.  Resultant Density Under Uniform D.eoxidation Conditions . . . .  8.  Comparison of Experimental and Theoretical S o l i d i f i c a t i o n  . •"  30 .  i l / / O i s f o r Various Metals  48  49  Porosity.. .: 9. 10.  Values of " 5 " L V 75" •  c o s  9  f o r  c o s  t l i e  36  § ^  o r  50  Various Systems  Copper-Silver-Iron System f o r Various Copper 5^  Concentrations 11.  Calculated Height of C a p i l l a r y Rise Using Equation 10  12.  Values of Parameters i n Equation 11  13»  Results of Sessile Drop Experiments  Ik.  Composition of Armco and Stelco M i l d Steel  15.  Calculated Values of l£SL  . . .  .  60 62  . . . . .  63 62  • •  ^7  INTRODUCTION  The  use  of i n f i l t r a t i o n  as a m e t a l l u r g i c a l p r o c e s s  has been  recognized  1 for  over t h i r t y - f i v e  converted  years.  However, o n l y r e c e n t t e c h n o l o g i c a l developments have  i t from an a r t t o a s c i e n c e . The  term i n f i l t r a t i o n r e f e r s t o the p r o c e s s where a l i q u i d  a porous s o l i d  s k e l e t o n r e s u l t i n g i n a dense two  phase m a t e r i a l .  penetrates  The  driving  f o r c e i s the r e s u l t a n t decrease i n o v e r a l l s u r f a c e f r e e energy of the system i s d i r e c t l y r e l a t e d t o the s u r f a c e e n e r g i e s  1.  and  of the i n d i v i d u a l components.  Wettability Any  d i s c u s s i o n of i n f i l t r a t i o n  w e t t a b i l i t y , which i s the a b i l i t y  phenomena must i n c l u d e an a n a l y s i s o f  o f the l i q u i d  phase to e l i m i n a t e the  solid-  vapour i n t e r f a c e by p e n e t r a t i n g through the channels of the porous s o l i d wetting  the s o l i d  the phases b e f o r e  phase.  E s s e n t i a l l y a c o n s i d e r a t i o n of the s u r f a c e e n e r g i e s  The  s u r f a c e e n e r g i e s o f the t h r e e i n t e r f a c e s can  r e p r e s e n t e d by the f a m i l i a r c o n t a c t angle r e l a t i o n s h i p which equates the t e n s i o n f o r c e s or s u r f a c e e n e r g i e s contact W i t h a s o l i d  sideration.  or  of  and a f t e r i n f i l t r a t i o n w i l l determine whether i n f i l t r a t i o n i s  thermodynamically f e a s i b l e .  t h i s simple  and  f o r a system of a s p h e r i c a l l i q u i d  and vapour phase.  c a s e i s i n e q u i l i b r i u m and  any  From f i g u r e 1 i t can be  cos  9  be  surface  drop i n  I t must be r e a l i z e d t h a t the system i n k i n e t i c e f f e c t s are not taken i n t o con-  seen t h a t  =  "ffsV  -  TTSL  () 2  - 2 where  = solid-vapour i n t e r f a c i a l  energy  "^SL = s o l i d - l i q u i d i n t e r f a c i a l  energy  2JLV  =  liquid-vapour i n t e r f a c i a l  energy  9 = c o n t a c t angle  F i g u r e 1:  ,  V e c t o r Diagram of Surface  Hence the c o n t a c t angle 9 i s a d i r e c t measure involved, system.  Forces  of the w e t t a b i l i t y o f the  system  the lower the c o n t a c t angle the h i g h e r i s the w e t t a b i l i t y f o r a g i v e n It  can be seen d i r e c t l y from e q u a t i o n 1 t h a t the c o n t a c t angle w i l l be  lower f o r : . (a)  a h i g h e r v a l u e of  iSsv  (b)  a lower v a l u e of  ~$*SL  (c)  a lower v a l u e o f  T^LV  - 3 -  U s u a l l y a c o n t a c t angle o f z e r o i s i n d i c a t i v e of a system t h a t wets t h i s i s a rather f i n e d at  9 4  although  a r b i t r a r y v a l u e as o t h e r authors have chosen w e t t i n g t o be d e -  30°  and even 9  ^ 9 0 °  The v a l u e s o f 1$ JJJ f o r metals  .  are the b e s t known of the t h r e e above  s u r f a c e e n e r g i e s w i t h l e s s b e i n g known about  a  -r  r  a n  TTQT  d  V  D  order.  2  f °  r  metals  i n that  DJ_i  T a y l o r ^ has t a b u l a t e d the known and e s t i m a t e d v a l u e s o f these t h r e e p a r a -  meters and i n g e n e r a l i f two of the t h r e e s u r f a c e e n e r g i e s are known a c o n t a c t angle experiment f a c i l i t a t e s  d e t e r m i n a t i o n of t h e . t h i r d .  A more  theoretical  treatment i s p r o v i d e d by Inman and T i p l e r ^ on the i n t e r f a c i a l e n e r g i e s metals  and a l l o y s .  iS^y  In g e n e r a l  cm^ and have temperature  i n c r e a s e with- i n c r e a s e  Combining t h i s f a c t w i t h the a n a l y s i s of m e t a l l a t t i c e mate can be made of  7^  JJJ^'.  from 1 0 - 3 0 $ h i g h e r than  r  the same m e t a l .  i s known about s o l i d - l i q u i d i n t e r f a c i a l e n e r g i e s tems have been d e t e r m i n e d .  The v a l u e o f  i s r e p o r t e d as 340 e r g s / c m 430 e r g s / c m  2  .  ~&sL ^  ergs/cm /°C.  c o h e s i v e energy, Du  "k i n g e n e r a l v a l u e s  Finally,, relatively  T  <  ^  o r  ^  n e  sys-  Jl  s o l i d - l i q u i d interface  is  of a p a r t i a l l y  l i q u i f i e d s i n g l e m e t a l system have been t a b u l a t e d ^ and t h e y range from 2 2 - 2 6 0 ergs/cm^ f o r those metals  studied.  These v a l u e s u s u a l l y can be c o r r e l a t e d  to  o n e - h a l f the heat o f f u s i o n of the m e t a l i n q u e s t i o n and i n t u i t i v e l y t h i s can be a s s o c i a t e d ^wteL-eh an i n t e r f a c e state.  produced when o n e - h a l f the atoms are  range  little  1^ ¥ ^ l e a d and s o l i d copper  and t h a t of l i q u i d c o p p e r . a n d s o l i d i r o n  V a l u e s of  an e s t i -  although values f o r c e r t a i n O  The  2  i n m e l t i n g temperature.  ?$"sv  L e s s i s known about  T ^ y f °  solid  v a l u e s range f o r metals from 1 0 0 - 1 8 0 0 e r g s /  c o e f f i c i e n t s i n the range of - . 0 1 to".k  s u r f a c e t e n s i o n s o f l i q u i d metals  of  i n the molten  2.  D r i v i n g Force f o r  Infiltration  The v a l u e of the d r i v i n g f o r c e f o r i n f i l t r a t i o n can be determined by a simple thermodynamic  -argument  i n v o l v i n g the  of the t h r e e i n t e r f a c e s t h a t are  important  s u r f a c e e n e r g i e s and s u r f a c e areas  in infiltration^namely,  solid-vapour,  ae"L op solid-liquid  and l i q u i d - v a p o u r .  I f we B O t u g * a n i n f i l t r a t i o n experiment  i n f i g u r e 2, where a porous^ s i n t e r e d m e t a l at  the b o t t o m ,  favourable, skeleton;  it  skeleton i s placed i n contact with a  i s evident that i f  c a p i l l a r y a c t i o n w i l l draw the  i.e.  infiltration will  as shown  s u r f a c e e n e r g i e s are l i q u i d up i n t o the  liquid  thermodynamically  channels  of  the  occur.  (,:,'/•, y ,  v />  i"  F i g u r e 2:  If particles  the  the  s o l i d metal  Infiltration  Skeleton  Liquid  Infiltrant  Experiment  skeleton i s constructed  s u r f a c e a r e a o f the  Porous  of 10 m i c r o n  s o l i d - v a p o u r i n t e r f a c e of a 2" x  spherical .326"  diameter  c y l i n d e r w i l l "be 8200 cm  which i s t h e a r e a of one 10 m i c r o n s p h e r i c a l  m u l t i p l i e d b y the number o f s p h e r i c a l The s o l i d - l i q u i d i n t e r f a c e a r e a ,  particles i n a cylinder  after i n f i l t r a t i o n ,  particle  of the s i z e  i s a l s o 8200 cm .  specified.  The l i q u i d -  2 vapour i n t e r f a c e b e f o r e i n f i l t r a t i o n i s "J .6k cm l"  x .325" diameter c y l i n d e r .  l i q u i d metal w i l l j u s t f i l l  and a f t e r  B  =  7-64 ~ t f  o f the s k e l e t o n  the v o i d s i n t h e s k e l e t o n .  energy b e f o r e i n f i l t r a t i o n F  I f the p o r o s i t y  which i s the s u r f a c e a r e a o f a i s 50$ a l l the  Hence,  the t o t a l  surface  is L V  Hf  8200  +  (3)  sv  infiltration  .  F  A  =  8200 " t f L S  +  l  where t h e l a s t term i n e q u a t i o n  k  -  2  "^LV  1  k i s a r e s u l t o f the l i q u i d - v a p o u r  interfacial  a r e a a f t e r i n f i l t r a t i o n and i s e q u a l t o the s u r f a c e a r e a o f a 2" x .326" d i a meter dense c y l i n d e r .  F  l n f  Hence,  thermodynamic  = can be approximated  F Using equation  8200  +  (75  sv  8  2  0  ~^SV "  0  -  tf ) SL  8  2  0  0  ^SL "  l  k  2  1  tf V  - 6.57  L  ^ L V  (5)  as  8200  ( tf  s  -  v  tf L)  ( ) 6  S  =  8200  - (  tf  Ly  cos 9  )  (7)  the d r i v i n g f o r c e f o r i n f i l t r a t i o n i s d i r e c t l y  r e l a t e d t o the p r o d u c t  ~L^LV cos 9 and n o t o n l y the c o n t a c t angle as g i v e n b y e q u a t i o n therefore,  '  1, E q u a t i o n 6 now becomes  F  Hence,  =  ^ i n f = Fg - F ^ o r  . 7.6k LV  this  driving force,  i s a necessary b u t not a s u f f i c i e n t  2.  Wetting,  condition f o r a large d r i v i n g  - 6 -  f o r c e f o r i n f i l t r a t i o n as not o n l y must 9 be s m a l l ^ t h i s b e i n g the s o l e requirement f o r wetting.but /  T$J_iV„ must T  be l a r g e .  T h i s i s e q u i v a l e n t t o s a y i n g t h a t the  the d i f f e r e n c e between the s o l i d vapour i n t e r f a c i a l energy and the s o l i d  larger  liquid  i n t e r f a c i a l energy the more f a v o u r a b l e w i l l be the c o n d i t i o n s f o r i n f i l t r a t i o n . 3-  Surface Films Any g r e a s e , a d s o r b e d - g a s e s ,  c h e m i c a l compound or any type of  f i l m p r e v e n t s t r u e m e t a l t o m e t a l c o n t a c t and thus d e c r e a s e s w e t t i n g . f i l m or adsorbed gas w i l l decrease 75* gy and hence i n f i l t r a t i o n .  surface Any oxide  Often there  a d i f f e r e n c e between the c o n t a c t angle when l i q u i d m e t a l i s a d v a n c i n g over a metal surface  and when i t  i s r e c e d i n g . The r e c e d i n g c o n t a c t angle i s  s m a l l e r due t o the a d s o r p t i o n o f l i q u i d s p e c i e s onto the case where the adsorbed s p e c i e s  increases  wetting.  solid,  this being a  However, i n g e n e r a l the  t o r e a c h the s o l i d s u r f a c e and hence a t t a i n an e q u i l i b r i u m c o n t a c t a n g l e , process  systems least  it  often i n v o l v i n g a s u b s t a n t i a l p e r i o d of time. i s i m p o s s i b l e t o get c o m p l e t e l y c l e a n s u r f a c e s  a stable  s u r f a c e monolayer p r e s e n t . o  pressure  .  surfilm  the  lat-  When d e a l i n g w i t h r e a l as t h e r e i s always  at  F o r example the b u l k . d e c o m p o s i t i o n  H  of Ag20 a t 9 3 0 C i s 1 . 7  at 9 3 0 C and 1 atm  solid  generally  f a c e s p e c i e s e i t h e r must be removed or the l i q u i d must d i f f u s e through the  ter  is  x 10  atm y e t t h e r e i s alwajjja t h i n o x i d e  layer  L i q u i d m e t a l - - m e t a l o x i d e systems do not g i v e a low  c o n t a c t angle u n l e s s some r e a c t i o n o c c u r s  i n Which the l i q u i d m e t a l d i s s o l v e s the  s o l i d metal oxide. The removal of greases and o x i d e f i l m s can be f a c i l i t a t e d by the  use  9  Of f l u x e s or d e t e r g e n t s .  Some work has been done i n t h i s r e g a r d  but there  is  ho g e n e r a l r u l e t h a t can be a p p l i e d t o a l l or even most systems as many e x p e r i ments u s u a l l y are r e q u i r e d t o determine the most s u i t a b l e f l u x .  Commercial f l u x i n g  procedure has almost always f o l l o w e d t h i s p r a c t i c e b u t nono the l e e s  is  well  - 7 -  established.  F l u x e s u s u a l l y are b e n e f i c i a l because  they c h e m i c a l l y d i s s o l v e any  oxide or grease on the s o l i d s u r f a c e b u t e l e c t r o c h e m i c a l t r a n s f e r f l u x has been o b s e r v e d .  The t r a n s f e r  through the  of t i n t o a copper s u r f a c e through a z i n c -  2 ammonium c h l o r i d e f l u x has been r e p o r t e d by B a i l e y and Watkins . k.  Surface,Roughness In p r e v i o u s c o n s i d e r a t i o n s o f c o n t a c t angle the s o l i d s u r f a c e was  assumed to be smooth b u t i n a c t u a l f a c t can be v e r y rough and i r r e g u l a r . the macroscopic roughness of any m e t a l s u r f a c e as  Besides  t h e r e i s another phenomenon known  g r a i n boundary w e t t i n g t h a t produces an even more n o n - p l a n a r s u r f a c e .  Because  g r a i n b o u n d a r i e s have a s s o c i a t e d w i t h them a h i g h e r f r e e energy than the b u l k lattice,  w e t t i n g and even p e n e t r a t i o n of them w i l l occur over and above t h a t of  the m e t a l s u r f a c e .  The e q u i l i b r i u m c o n d i t i o n can be d e s c r i b e d by the  dihedral  a n g l e which i s the angle produced at the g r a i n - b o u n d a r y - l i q u i d i n t e r f a c e when t h e g r a i n boundary i s  p r e f e r e n t i a l l y e t c h e d by the l i q u i d m e t a l .  seen i n f i g u r e 3*  F i g u r e 3-  G r a i n Boundary G r o o v i n g  T h i s can be  -8 T h i s angle i s d e f i n e d by the f o l l o w i n g e q u a t i o n from which i t when cos  0/2  complete p e n e t r a t i o n o f the g r a i n s ' b o u n d a r i e s w i l l O c c u r .  = 1,  = where It  $S  ^  s  (8)  4  the s o l i d - s o l i d i n t e r f a c i a l energy or g r a i n boundary energy.  i s e a s i l y seen t h a t t h i s phenomenon w i l l i n c r e a s e  liquid interface.  ....  cos 0'  It  can.be  the t r u e  5'  solid-  roughness  10  was f i r s t d i s c u s s e d by Wenzel  , who proposed the r e l a t i o n s h i p  -  r cos 9  9'  -•- observed c o n t a c t angle  9  •- t r u e  r  the s u r f a c e a r e a o f the  The r e l a t i o n s h i p between c o n t a c t angle and s u r f a c e  . .  where  can be seen t h a t  (9)  contact angle , ., . tapparent r u e s u r f ascuer f aacree a a r e a = roughness r a t i o =  seen from e q u a t i o n 9 t h a t the apparent c o n t a c t angle i s always l e s s  than  contact angle.  E f f e c t of Temperature on I n f i l t r a t i o n The temperature  c o e f f i c i e n t of l i q u i d s u r f a c e t e n s i o n s f o r metals  varies  2from -.0') t o  =.k  ergs/cm/°C.  Very l i t t l e i s known about the temperature  cient of solid-vapour tension i n metals, of s i m i l a r s i g n as t h a t f o r l i q u i d s . such as G r e o n o u g h ' s of the temperature able. as "73  11  estimate  b u t i n t u i t i v e l y the c o e f f i c i e n t  T h i s i s i n agreement  would be  with i s o l a t e d Values  of -0.6 e r g s / c m / ° C f o r s o l i d n i c k e l . 2  coeffi-  No v a l u e s  dependence of the s o l i d - l i q u i d - i n t e r f a c i a l energy are t & v a i l -  In g e n e r a l , however, the temperature c o e f f i c i e n t would l i k e l y be n e g a t i v e i s a measure of the d i s r e g i s t r y between the two phases, and i n c r e a s i n g  DIJ  the temperature  would i n g e n e r a l i n c r e a s e  the d i s r e g i s t r y o r  l^at .  the  s o l u b i l i t i e s and hence decrease  From e q u a t i o n 2 i t as the temperature  increases  can be seen t h a t . i f  a l l three  the c o n t a c t angle w i l l p r o b a b l y d e c r e a s e ,  v a l u e o f 9 depending upon the magnitude of the temperature consistent with experimental  surface energies the  coefficients.  actual This  is  findings.  An i n t e r e s t i n g phenomenon o c c u r s w i t h some systems m e t a l l i c compounds are formed at  the  of the c o p p e r - t i n - ^ 7 u  phase.  i n which  solid-liquid interface.  l e a d a l l o y g i v e s a s t a b l e c o a t i n g on copper below 3 8 0 ° C , erature  decreased  inter-  F o r example a t i n -  the d e c o m p o s i t i o n temp-  Above t h a t temperature  the c o n t a c t angle .  2 increases  and d e w e t t i n g o c c u r s  f o r m a t i o n of the if  .  The- i n c r e a s e  i n c o n t a c t angle i s due t o  phase which does not f a v o u r a h i g h degree of w e t t i n g .  w e t t i n g d a t a are  g i v e n f o r one temperature  and may w e l l decrease  Hence  i n a system i n which an i n t e r -  m e t a l l i c compound i s f o r m e d , i n c r e a s i n g the temperature increase,  the  does not  necessarily  wetting.  E q u a t i o n 10 below g i v e s a f o r m u l a f o r the e q u i l i b r i u m h e i g h t t o which a l i q u i d w i l l r i s e i n a c a p i l l a r y of radius r . respect  Simple d i f f e r e n t i a t i o n w i t h  t o temperature w i l l g i v e the c o r r e s p o n d i n g temperature  h  =.  2  T& L V /O  C  O  S  coefficient.  9  g r  (10)  and  "KLVCOS 9 d / ° ' dT  where  = the d e n s i t y of the l i q u i d m e t a l g = acceleration  If  \(ll)  d t f L Y and cbQ "dT  dT  of  gravity  are known a simple experiment y i e l d i n g the v a r i a t i o n of  - 10 -  c o n t a c t angle w i t h temperature  w i l l g i v e the d e s i r e d temperature  h e i g h t of r i s e of a l i q u i d i n a c a p i l l a r y .  The s i g n of t h i s parameter  w i t h the a c t u a l magnitude of the t h r e e temperature i n equation  11.  6.  Infiltration  Rate of  It  coefficient  of  w i l l vary  dependent terms on the  right  i s g e n e r a l l y known t h a t . i n f i l t r a t i o n i n a f a v o u r a b l e system t a k e s 12  p l a c e i n a r e l a t i v e l y s h o r t time  .  Where*s,\ i n commercial p r a c t i c e  porous  s k e l e t o n s are o f t e n h e l d i n the l i q u i d b a t h f o r s u b s t a n t i a l time i n t e r v a l s , is  o n l y to change the p r o p e r t i e s  sintering.  Because  of the composite by a l l o y i n g or l i q u i d  the d r i v i n g f o r c e  this  phase  i n i n f i l t r a t i o n i s i d e n t i c a l to that i n  l i q u i d phase s i n t e r i n g any knowledge of the r a t e or mechanism o f i n f i l t r a t i o n may be d i r e c t l y a p p l i e d t o l i q u i d phase  sintering.  L i g e n z a and B e r n s t e i n -> have d e r i v e d a d i f f e r e n t i a l e q u a t i o n o f motion for  the f l o w of l i q u i d s through f i n e c a p i l l a r i e s assuming P o i y s e u i l l e ' s Law h o l d s  and t h a t w e t t i n g i s v e r y r a p i d . (.002 -  They used v e r y f i n e c a p i l l a r y r a d i u s g l a s s  .005 cm) w i t h s e v e r a l o r g a n i c l i q u i d s .  mental r e s u l t s  and t h e o r y was e x c e l l e n t .  Agreement between t h e i r  tubes  experi-  The d i f f e r e n t i a l e q u a t i o n which they  d e r i v e d i s as f o l l o w s .  = 2TT R ?X C  dt  where  h = h e i g h t of r i s e  cos  9  of the column o f l i q u i d a t time  = radius of c a p i l l a r y 1 = length of c a p i l l a r y  (12)  t  - 11 ffts = v i s c o s i t y o f /7L  = v i s c o s i t y of  &  = density of  yO /O  liquid  = density of  a  air  liquid air  = l i q u i d - v a p o u r surface 9 = contact  angle  g = acceleration  It  energy  due t o  gravity  can be seen from the above e q u a t i o n t h a t the term on the r i g h t hand  s i d e i s the d r i v i n g f o r c e  f o r i n f i l t r a t i o n , namely,  the change i n s u r f a c e  energies  due t o w e t t i n g o f the  C a p i l l a r y tubes by the l i q u i d .  The r e s i s t a n c e f o r c e s  the terms on the l e f t  hand s i d e and a r e ,  f o r c e due to the change  momentum o f the l i q u i d mass,  end d r a g e f f e c t ,  E q u a t i o n 12 i s not amenable to e x p l i c i t ; s m a l l r a d i u s the r a t e o f change neglected.  respectively  v i s c o u s r e s i s t a n c e and  are in  gravity.  s o l u t i o n b u t f o r a tube of s u f f i c i e n t l y  of momentum and the end d r a g e f f e c t terms may be  The v a l i d i t y of t h i s assumption was e s t a b l i s h e d by L i g e n z a " and B e r n s t e i•n 1 3  by g r a p h i c a l d i f f e r e n t i a t i o n of t h e i r e x p e r i m e n t a l  data.  lk Semlak and Rhines  a p p l i e d the above a n a l y s i s t o a system  of a porous m e t a l powder s k e l e t o n and a l i q u i d m e t a l i n f i l t r a n t . t h a t the t o r t u o u s analogous system.  channels r e s u l t i n g from the  consisting  They assumed  s i n t e r i n g of m e t a l powders  to f i n e c a p i l l a r i e s and t h a t e q u a t i o n 12 c o u l d be a p p l i e d t o T h e i r approximate  are  this  s o l u t i o n o f the above d i f f e r e n t i a l e q u a t i o n y i e l d e d  an e x p r e s s i o n f o r the h e i g h t of i n f i l t r a t i o n as a f u n c t i o n of time as f o l l o w s ;  f R ^ M h  The 2/rr  =  #  {  correction  cos  - 3 ^  9  t ^  l  /  g  (13)  J  i s made to a l l o w f o r the  c a p i l l a r i e s i n a powder s k e l e t o n compared £ 0 * the  s e m i - c i r c U l a r i t y of  straight  the  c a p i l l a r i e s used by  -  L i g e n z a and B e r n s t e i n R ,  13  .  the c a p i l l a r y r a d i u s .  D i f f i c u l t y arises  i n the e v a l u a t i o n o f the  In a powder compact the r a d i i  powder p a r t i c l e are c o n s t a n t l y  12  -  parameter  of the pores between  the  changing b o t h i n shape and s i z e and any s i n g l e v a l u e 13  o f t h i s parameter a value o f R  c  can o n l y be an a p p r o x i m a t i o n .  e q u a l t o one q u a r t e r  s k e l e t o n was a r e a s o n a b l e ations.  felt  J  of the measured mean f r e e p a t h o f the  a p p r o x i m a t i o n and t h i s v a l u e was used i n t h e i r  T h e i r e x p e r i m e n t a l t e c h n i q u e was t o s i n t e r  a porous s k e l e t o n which was immersed at g i v e n s h o r t p e r i o d s of t i m e . by  Semlak and Rhines  l o o s e m e t a l powders  that sintered calculto.obtain  one end i n t o a b a t h of l i q u i d m e t a l  They t h e n e v a l u a t e d the h e i g h t of i n f i l t r a t i o n s i m p l y  s e c t i o n i n g the composite l o n g i t u d i n a l l y and measuring the h e i g h t of r i s e  metal with a r u l e r .  The times used i n t h e i r experiments  from 1 to 7 seconds. with theory,  for  Although t h e i r r e s u l t s  were v e r y s h o r t v a r y i n g  were a p p a r e n t l y i n good  t h e i r technique i n h e r e n t l y lends i t s e l f to large e r r o r s  w i t h the d i f f i c u l t y of measuring these s h o r t times a c c u r a t e l y . r a t e o f i n f i l t r a t i o n Of l i q u i d l e a d a t  of  v a r i o u s temperatures  agreement associated  By c a l c u l a t i n g  the  t h e y o b t a i n e d an  a c t i v a t i o n energy of 4000 + 660 c a l / m o l e which compares f a v o u r a b l y w i t h those for  v i s c o u s f l o w and s e l f d i f f u s i o n i n l i q u i d l e a d . However,  and  strictly  t h e i r a c t i v a t i o n energies  were b a s e d on a r a t e of ^ l / g  speaking t h i s i s not a t r u e r a t e compared t o  ~ . The t r u e dt a c t i v a t i o n energy must be determined at v a r i o u s temperatures u s i n g an Arrhenius , i . , ,. . ,. p l o t and at constant times as  7.  dh ... dh ( 2 t / ) TT ~ tT dt dt X  2  Solubility. In  i n f i l t r a t i o n the c o m p o s i t i o n of the i n f i l t r a n t i s g e n e r a l l y  by  the s o l u b i l i t y o f the  s o l i d phase i n the l i q u i d m e t a l phase.  is  made to p r e s a t u r a t e the l i q u i d i n f i l t r a n t w i t h the  s o l i d at  governed  I f no p r o v i s i o n the  temperature  of i n f i l t r a t i o n then s u b s t a n t i a l e r o s i o n Or s o l u t i o n Of the porous s k e l e t o n aild even c o l l a p s e of the  s k e l e t o n may o c c u r .  occurs  - 13 -  It  i s g e n e r a l l y agreed t h a t some s o l u b i l i t y between the l i q u i d and s o l i d  phases i s r e q u i r e d b e f o r e good w e t t i n g o c c u r s .  Increased  solubility will  decrease  the magnitude o f the s o l i d - l i q u i d i n t e r f a c i a l energy and as d i s c u s s e d b e f o r e w i l l promote a lower c o n t a c t a n g l e .  However, i n the  system c o p p e r - t u n g s t e n  this there  i s v i r t u a l l y no s o l u b i l i t y y e t i n f i l t r a t i o n o c c u r s r e a d i l y .  8.  S o l u t e A d d i t i o n s t o the L i q u i d Phase I n c e r t a i n cases the a d d i t i o n o f minor amounts of a s o l u t e t o the  phase r e s u l t s eristics results  liquid  i n s u r f a c e phenomena which f a v o u r a b l y change the w e t t i n g c h a r a c t -  o f a system.  The a d d i t i o n of a s u r f a c e a c t i v e m e t a l t o the l i q u i d  i n p r e f e r e n t i a l a d s o r p t i o n and a l o w e r i n g o f the  surface free  phase  energy.  T h i s can be d e s c r i b e d q u a n t i t a t i v e l y b y the Gibbs a d s o r p t i o n i s o t h e r m : d ~£ LV RT I n d a i  where \~± = s u r f a c e excess of component d  -rf  i  . LV = change i n l i q u i d - v a p o u r s u r f a c e  tension  d-ai = change i n a c t i v i t y of the i . t h component I f the a d d i t i o n of a s u r f a c e  active  s o l u t e produced o n l y a decrease i n the  liquid  vapour s u r f a c e t e n s i o n , t h i s would r e s u l t i n an u n f a v o u r a b l e change w i t h r e s p e c t to i n f i l t r a t i o n . change i n the  But a s s o c i a t e d w i t h t h i s  surface  a c t i v i t y of the s o l u t e i s  s o l i d - l i q u i d i n t e r f a c i a l energy and b o t h these f a c t o r s  c o n s i d e r e d when d e t e r m i n i n g the net e f f e c t  on i n f i l t r a t i o n .  must be  a  - Ik -  EXPERIMENTAL  1.  Materials a.  Powder In o r d e r t o produce a porous s k e l e t o n of w e l l d e f i n e d geometry,. s p h e r i c a l  i r o n and n i c k e l powders were used i n t h i s work.  The f l i c k e l was s u p p l i e d by  S h e r r i t t - G o r d o n Mines L i m i t e d i n t h r e e s i z e f r a c t i o n s ; mesh and 10 m i c r o n s .  -20 +35 mesh,  -50 +100  A -100 +150 mesh f r a c t i o n of Armco i r o n powder was o b t a i n e d  by s c r e e n i n g a s - r e c e i v e d  powder s u p p l i e d by F e d e r a l Mogul C o r p o r a t i o n .  Composi-  t i o n of these powders was as f o l l o w s :  Iron  Nickel  99-9+  Fe  Ni"*  C  .012  Co  .16  Mn  .017.  Cu  .005  S  .025  Fe.-  P  .010  s  .003  C  .006  *  b.  99-9  .004  i n c l u d e s Co.  Infiltrant High p u r i t y c o p p e r ,  c o n t a c t angle  lead,  and s i l v e r were used as i n f i l t r a n t s and f o r  studies.  Pb  99-99  ( C o n s o l i d a t e d M i n i n g and S m e l t i n g Company)  Ag  99'99  ( C o n s o l i d a t e d M i n i n g and S m e l t i n g Company)  Cu  99'90  (Metals D i s i n t e g r a t i n g Company)  - 15 2. . S k e l e t o n P r e p a r a t i o n N i c k e l or i r o n powder was p l a c e d i n a 2 i n . l o n g x  .325 i n . I . D .  q u a r t z tube w i t h a t a p e r e d carbon p l u g and s i n t e r e d under a f l o w o f ammonia-in a v e r t i c a l r e s i s t a n c e tube f u r n a c e .  cracked  The f i n e r powders were  first  v i b r a t e d f o r two minutes on a S y n t r o n v i b r a t o r t o minimize b r i d g i n g and t o e n sure u n i f o r m i t y .  About 25 minutes was r e q u i r e d t o b r i n g the f u r n a c e up to  t e r i n g temperatures.  sin-  S i n c e no d e n s i f i c a t i o n of the compact was d e s i r e d the  t e r i n g , c o n d i t i o n s chosen were b a s e d on the p a r t i c l e g i v e n i n T a b l e I were found t o be  size.  The  sin-  temperatures  satisfactory. TABLE I  S i n t e r i n g Conditions f o r Skeleton Preparations  Powder  Sintering Conditions  -100 +150 Fe  1 hr.  -20  +35 N i  1 h r . 1000°C  -50  +100 N i  1 hr.  900°C  1 hr.  750°C  10 u  Ni  900°C  D e n s i t i e s o b t a i n e d under these c o n d i t i o n s ranged from 53$ of t h e o r e t i c a l f o r f i n e r powders t o 64$ of t h e o r e t i c a l 3-  the  f o r the c o a r s e powders.  I n f i l t r a t i o n Procedure I n f i l t r a t i o n was c a r r i e d out u s i n g a v e r t i c a l K a n t h a l A - l - w o u n d  tance f u r n a c e w i t h a c e n t r a l 1" q u a r t z t u b e .  The i n f i l t r a n t was p l a c e d i n the  bottom o f a 0.8" diameter x 3" l o n g carbon mold w i t h a .3^0" mold c a v i t y t rally drilled.  resis-  cen-  I n the e a r l i e r work the porous s k e l e t o n was p l a c e d on t o p o f  the i n f i l t r a n t ' i n s i d e the carbon mold and the temperature t r o l l e d by a v a r i a b l e powerstat  of the f u r n a c e c o n -  and a Model 4o4 Wheelco c o n t r o l l e r w i t h a  - 16 - , c h r o m e l - a l u m e l thermocouple.  Hydrogen.  d i z e d and d r i e d tank d e o x i d a t i o n of the restricted  A hydrogen atmosphere  was o b t a i n e d by u s i n g d e o x i -  However t h i s procedure d i d not f a c i l i t a t e  s k e l e t o n as the f l o w of hydrogen through the  by the m o l d .  In l a t e r work the  uniform  s k e l e t o n was  same f u r n a c e was u s e d , b u t the  skeleton  was supported b y two chromel wires r u n n i n g through a f i n e d o u b l e - h o l e d 16" alumina r o d .  T h i s r o d was a t t a c h e d to a s m a l l winch by a f i n e t h r e a d which a l -  lowed the l o w e r i n g of the s k e l e t o n i n t o the m o l d .  A f t e r the  s k e l e t o n had been  d e o x i d i z e d f o r 15 minutes i n the f r e e hydrogen f l o w , i t was lowered i n t o the mold and h e l d at  a p o s i t i o n 2 mm. above the m o l t e n . b a t h .  severed a l l o w i n g i n f i l t r a t i o n to o c c u r .  The f i n e t h r e a d was t h e n  A m i l l i m e t e r s c a l e was a t t a c h e d t o  top of the q u a r t z tube b e h i n d the alumina r o d such t h a t the motion o f the t o n i n t o the molten i n f i l t r a n t c o u l d be r e c o r d e d . i s shown i n F i g u r e  k.  A diagram of the  the  skele-  apparatus  h.  Rate Measurements The r a t e o f i n f i l t r a t i o n was measured by r e c o r d i n g the motion o f  alumina r o d a g a i n s t  the m i l l i m e t e r s c a l e w i t h a 16 mm B e l l and Howell Canonet  movie camera r u n n i n g a t of.the  a speed of 24 frames per second.  i n d i c a t o r i n each frame o f the movie f i l m when  i t was p o s s i b l e t o determine creased.  the  skeleton.  5•  D e n s i t y Measurements  d e v e l o p e d and  projected,  the r a t e at which the h e i g h t of the molten b a t h d e -  T h i s was then r e l a t e d  the  By n o t i n g the p o s i t i o n  to the r a t e of i n f i l t r a t i o n o f molten m e t a l  into  The d e n s i t y of the f i n a l i n f i l t r a t e d specimen was determined by the f o l l o w i n g procedure.  The d e n s i t y of the  by measuring a c c u r a t e l y then w e i g h i n g i t ,  s k e l e t o n was f i r s t  determined s i m p l y  the volume o f the c y l i n d i c a l s k e l e t o n w i t h c a l i p e r s  the d e n s i t y b e i n g e x p r e s s e d  as a percentage o f a s i m i l a r  and solid  - 17 -  RV  -Winch  L  u  -Thread  Vernier  Scale  Alumina  o lo o o o o o  H  F i g u r e k:  Schematic  Porous  Indicator  Skeleton  Carbon Mold Liquid  2  Diagram o f I n f i l t r a t i o n Apparatus  Infiltrant  - 18 -  cylinder.  A f t e r i n f i l t r a t i o n the composite was machined i n t o a c y l i n d e r and the  volume and weight a c c u r a t e l y d i d not change  measured.  The assumption was made t h a t the  shape upon i n f i l t r a t i o n and u s i n g t h i s ,  weight of the h i g h e r m e l t i n g p o i n t phase,  skeleton  the volume and hence  was d e t e r m i n e d .  The weight of the  phase was simply the d i f f e r e n c e between the t o t a l weight and t h a t o f the m e l t i n g point phase. phase.  density,  as a percentage o f t h e o r e t i c a l ,  Volume phase 1 + volume phase 2 T o t a l volume  the r a t i o  . x  1 0 0  . /°-  other  higher  T h i s e n a b l e d the d e t e r m i n a t i o n of the volume of the  The f i n a l r e s u l t a n t  the  second  i s simply  An e s t i m a t i o n of  the  a c c u r a c y o f t h i s method i s g i v e n i n Appendix I .  6.  Metallography In o r d e r t o determine  the mean f r e e path i n the porous s k e l e t o n a met2k  a l l o g r a p h i c a n a l y s i s was made.  The t e c h n i q u e used was t h a t o u t l i n e d by G u r l a n d  which g i v e s the mean f r e e path as a f u n c t i o n " o f the volume p e r c e n t number o f p a r t i c l e s relation is  intersected  by a random s t r a i g h t  and the  average  l i n e of unit length.  This  shown i n e q u a t i o n l U .  A  where  = mean f r e e V  a  =  1  - Va %  (Ik)  path  = volume f r a c t i o n o c c u p i e d by the  N-p = number o f p a r t i c l e s  The porous s k e l e t o n s  intersected  particles by a random l i n e o f u n i t  length  c o u l d not be mounted and p o l i s h e d as the p a r t i c l e s would  t e a r away due t o the weakly s i n t e r e d b o n d s .  Hence the  s k e l e t o n s were f i r s t i n -  f i l t r a t e d w i t h t i n and subsequent p o l i s h i n g and l a p p i n g was s u c c e s s f u l .  An  o c u l a r l e n s w i t h a c r o s s h a i r attachment was used on a R e i c h e r t microscope the number of p a r t i c l e s  intersected  by t h i s  cross h a i r ,  whose l e n g t h was  and  later  - 19 d e t e r m i n e d , was r e a d d i r e c t l y from the m i c r o s c o p e , mean f r e e p a t h .  T h i s mean f r e e p a t h was used i n l a t e r  culations.  7.  e n a b l i n g the c a l c u l a t i o n of  the  r a t e of i n f i l t r a t i o n c a l -  !  S e s s i l e Drop Experiments C o n t a c t angle experiments were c a r r i e d out under hydrogen i n a s m a l l  h o r i z o n t a l q u a r t z tube f i t t e d w i t h a h i g h f r e q u e n c y i n d u c t i o n c o i l .  A s m a l l semi-  c y l i n d r i c a l s t e e l b o a t was f i t t e d w i t h a chrome1-alumel thermocouple from which the temperature  was r e a d by means o f a Pye p o t e n t i o m e t e r .  Armco i r o n and S t e l c o m i l d s t e e l  Sherritt-Gord<on  sheet were used as the s u b s t r a t e s i n these  The n i c k e l sheet was p r e p a r e d by S h e r r i t t - G o r d o n f r o m powder by d i r e c t and subsequent p r o c e s s i n g . essary  to sinter  -325  p r i o r t o the  tests.  rolling  In o r d e r to produce t h i n Armco i r o n sheet i t was n e c -  mesh Armco i r o n powder f o r  l6 hours  at  1300°C i n c r a c k e d  ammonia and then t o c o l d r o l l the s i n t e r e d body a p p r o x i m a t e l y 80$. the s u b s t r a t e  nickel,  In each case  was p o l i s h e d t o a 2/0 f i n i s h and reduced i n hydrogen immediately s e s s i l e drop  experiment.  0.6 cm  Small d i s c s approximately  i n diameter  phase were produced by c a s t i n g and m a c h i n i n g .  xO.25 cm of the m e l t i n g  Each d i s c was a c c u r a t e l y  weighed  and the a r e a o f spread r e s u l t i n g from w e t t i n g was measured w i t h a compensating polar planimeter a f t e r s o l i d i f i c a t i o n .  8.  Measurement of C o n t a c t Angle  l8 a.  B a s h f o r t h and Adams  Technique/  The c o n t a c t angle f o r most m e t a l l i c systems and Adams t e c h n i q u e i s q u i t e simple to a p p l y .  i s a c u t e , and the B a s h f o r t h  The c o n t a c t angle i s g i v e n by  e q u a t i o n 15. 9 = 2 tan  - 1  x  /,.->,  (15)  - 20 where h and x are substrate,  the h e i g h t of the drop and r a d i u s of the c i r c u l a r  respectively.  d r o p i s a segment  The assumption i n e q u a t i o n 15  i s t h a t the shape of  the  of a sphere and t h i s assumption i s q u i t e v a l i d f o r s m a l l drops  where d i s t o r t i o n from s p h e r o i d i c i t y by g r a v i t y i s i s measured d i r e c t l y w i t h  b.  a r e a on the  small.  The h e i g h t of the drop  calipers.  Volume o f Drop Method " Another method can be d e v e l o p e d to determine  9 by c a l c u l a t i n g the volume  of the drop and knowing the a r e a under the drop and d e n s i t y o f the l i q u i d The formulaea f o r t h i s method are d e r i v e d i n Appendix I I . B a s h f o r t h and Adams t e c h n i q u e the  The area,  metal.  A g a i n as i n the  shape of the drop i s assumed to be  spherical.  under the drop was measured u s i n g a K e u f f e l and E s s e r  comp-  2 e n s a t i n g p o l a r planimeter w i t h ' a n a c c u r a c y o f +  .02 cm .  I t was f e l t t h a t  greater  a c c u r a c y would be o b t a i n e d i n the B a s h f o r t h and Adams t e c h n i q u e by t a k i n g r = where A i s the a r e a as determined w i t h the p l a h i m e t e r r a t h e r than measured v a l u e s o f r d i r e c t l y from the d r o p .  averaging  - 21 RESULTS AND DISCUSSION  1.  I n f i l t r a t i o n Mechanism By a n a l y s i n g the f l o w of the l i q u i d I n f i l t r a n t  i n t o and through the  channels o f the porous s k e l e t o n an i n f i l t r a t i o n mechanism can be e s t a b l i s h e d . C o n c e i v a b l y the l i q u i d m e t a l c o u l d i n f i l t r a t e the s k e l e t o n i n two ways. t h e l i q u i d c o u l d wet the s u r f a c e o f the p a r t i c l e s c o a t i n g on a l l the p a r t i c l e s  with a t h i n f i l m replaces  l i q u i d interface than the f o r m e r .  resulting in a thin liquid  a f t e r which i n f i l t r a t i o n of the l i q u i d i n t o t h e s e  i n f i l t r a n t - c o a t e d channels would o c c u r . the p a r t i c l e s  First  T h i s i s f e a s i b l e s i n c e the c o a t i n g the s o l i d - v a p o u r i n t e r f a c e  with a  of  solid  and, as has been shown, the l a t t e r i s n o r m a l l y of lower energy S i n c e the channels o f the s k e l e t o n now c o n s i s t  l i q u i d m e t a l as the i n f i l t r a n t , w e t t i n g i s p e r f e c t  of the same  and i n f i l t r a t i o n w i l l  occur.  In t h i s case i n f i l t r a t i o n w i l l be n o n - u n i f o r m and t h e r e w i l l be no p l a n a r  inter-  f a c e of advancing l i q u i d as i n f i l t r a t i o n o c c u r s .  The second i n f i l t r a t i o n mechanism i s i n a single wetting process.  s i m p l y the f i l l i n g  There i s no p r i o r p a r t i c l e  mechanism and the i n f i l t r a t i o n i n t e r f a c e  of the  channels  c o a t i n g as i n the  i s assumed t o be p l a n a r .  In o r d e r t o determine which of the above mechanisms i s o p e r a t i n g e r a l s k e l e t o n s were i n f i l t r a t e d w i t h l e s s pores i n the m e t a l s k e l e t o n .  l i q u i d than r e q u i r e d to f i l l  sevthe  particles  of c a p i l l a r y r a d i u s on i n f i l t r a t i o n mechanisms.  N e i t h e r i n the case o f the f i n e (10 u p a r t i c l e  size)  nor the  (-50 +100 mesh) c a p i l l a r y s k e l e t o n d i d p r i o r c o a t i n g o f the p a r t i c l e s Sample 86 i s  all  S k e l e t o n s i n v o l v i n g two d i f f e r e n t s i z e s o f  were used t o determine the e f f e c t  above  coarse occur.  -50 +100 mesh n i c k e l i n f i l t r a t e d w i t h s u f f i c i e n t s i l v e r to f i l l  30$ of the a v a i l a b l e p o r e s ,  only  t h i s c o r r e s p o n d i n g t o a h e i g h t of r i s e of- s i l v e r o f  - 22 -  0.6k i n c h e s i n the s k e l e t o n i f no p r i o r c o a t i n g o c c u r r e d .  F i g u r e 5 shows t h a t  the s i l v e r rose t o o n l y 0.6k i n c h e s of a p o s s i b l e 1 . 9 5 inches- and no s i l v e r was i n evidence above t h i s l e v e l .  The i n t e r f a c e  was p l a n a r and the i n f i l t r a t e d r e -  g i o n was c o m p l e t e l y dense.  In the p r i o r c o a t i n g argu/ment i t  i s d i f f i c u l t t o envisage the  trans-  p o r t of s u f f i c i e n t mass o f l i q u i d i n f i l t r a n t through a t h i n c o a t i n g to a l l o w the advance of f i l m f o r m a t i o n on the s k e l e t o n c h a n n e l s . does a l l o w the replacement  t i o n of a liquid-vapour interface Hence i t  process  of the s o l i d - v a p o r i n t e r f a c e b y a s o l i d - l i q u i d  f a c e r e s u l t i n g i n a decrease i n surface  s u r f a c e -energy.  A l t h o u g h the c o a t i n g  f r e e energy,  inter-  t h e r e i s however, the  w i t h which t h e r e i s a s s o c i a t e d . a n  i s b e l i e v e d t h a t p r i o r c o a t i n g does n o t ,  crea-  increase  of  i n general,  occur.  Whereas i n the c o a r s e r p a r t i c l e o b t a i n e d was p l a n a r ,  s k e l e t o n s the i n f i l t r a t i o n i n t e r f a c e  t h i s was not the case i n the f i n e ( 1 0 )x)  skeletons.  Samples  7^ and 75 were i n f i l t r a t e d w i t h 1+3$ and 2k°fo of the amount o f s i l v e r r e q u i r e d t o fill.the  pores.  I n b o t h cases i n f i l t r a t i o n was u n i f o r m .  Table II  d e n s i t y as a f u n c t i o n o f d i s t a n c e up the composite f o r sample 7 5 t h e presence later,  shows the i n spite  o f the p r e f e r e n t i a l o x i d a t i o n phenomenon which w i l l be d i s c u s s e d  the d e n s i t y does not v a r y a g r e a t d e a l , the average b e i n g 7 5 - 3 $ of  retical.  of  S i n c e the amount of s i l v e r used was s u f f i c i e n t t o i n c r e a s e  2 ^ . 0 $ and the d e n s i t y of the n i c k e l compact was o r i g i n a l l y 5 2 ' ^ the  the  theodensity  average  d e n s i t y s h o u l d be 7 6 . 4 $ ' w h i c h compares f a v o r a b l y , w i t h . t h e e x p e r i m e n t a l l y  deter-  mined v a l u e .  The e x p l a n a t i o n f o r the u n i f o r m low d e n s i t y i n the f i n e s k e l e t o n s and the c o m p l e t e l y p l a n a r i n t e r f a c e relative  tortuosities  i n the c o a r s e r s k e l e t o n s  o f the two s k e l e t o n s .  is felt  to l i e i n the  Since the 1 0 micron powder was not  F i g u r e 5;  Infiltration  of Specimen 86 w i t h 30$ R e q u i r e d S i l v e r  - 24 c l o s e l y s i z e d , a h i g h e r d e n s i t y s k e l e t o n than t h a t made o f more c l o s e l y s i z e d , powder r e s u l t s  and because  of t h i s the  s k e l e t o n w i l l have a h i g h e r  TABLE  tortuosity.  II  D e n s i t y D i s t r i b u t i o n f o r Specimen 74  ,Distance From Bottom  . Resultant Density ($ o f T h e o r e t i c a l )  0.5 cm  73-1  :  1.0  73-4  1-5  73.1  2,0  76.0  2.5'  76.8  3-0  77-2  3-7  78.2  The main r e s i s t a n c e t o i n f i l t r a t i o n i s the v i s c o u s d r a g of the  liquid  m e t a l and t h i s r e s i s t a n c e w i l l be h i g h e r i f the c a p i l l a r i e s are f i n e r and more tortuous.  Because o f the n a t u r e  of a s k e l e t o n made from s i n t e r e d powders t h e r e  w i l l n e c e s s a r i l y be c a p i l l a r i e s o f v a r y i n g t o r t u o s i t y t o i n f i l t r a t i o n w i l l a l s o v a r y through the compact. m e t a l f l o w s up the pores behind.  and hence the It  i s f e l t t h a t the  When t h e r e i s a shortage o f i n f i l t r a n t these pores w i l l  w i l l be f i l l e d  finer particle  74 and the p o r o s i t y s t r u c t u r e  free  speak of an i n f i l t r a t i o n " i n t e r f a c e "  sizes.  of  It  pores  energy. when c o n -  F i g u r e 6 shows a photo m i c r o g r a p h of  can be seen.  course  infiltrant a l l  i n o r d e r t o f u r t h e r d e c r e a s e the o v e r a l l s u r f a c e  i s not a p p r o p r i a t e t o  s i d e r i n g the  liquid  s k e l e t o n through the channels o f l e a s t r e s i s t a n c e l e a v i n g  not be f i l l e d b u t i n the normal case when t h e r e i s adequate  Hence i t  resistance  sample  i s n o t a b l e t h a t t h e r e i s no e v i -  dence o f p r i o r c o a t i n g of the s k e l e t o n c a p i l l a r i e s by the i n f i l t r a n t , i n a g r e e ment w i t h the i n f i l t r a t i o n mechanism proposed above.  Specimen 7 4 Showing R e s i d u a l P o r o s i t y Regions of H i g h T o r t u o s i t y X1 0 0 0 .  at  26  Annular  Space  •315"-  -Alumina Rod  Chrome1 Wire  Annular  Porous  Space  Skeleton  Carbon Mold  Liquid  ^-.329" Figure  7•  Infiltrant  -1  Geometry o f I n f i l t r a t i o n Mold and Porous  Skeleton  - 27 -  2.  Rate o f I n f i l t r a t i o n a.  A n a l y s i s o f E x p e r i m e n t a l Geometry As o u t l i n e d i n the procedure  i n f i l t r a t i o n commences  the f i n e t h r e a d s u p p o r t i n g the alumina r o d i s c u t . if  The s k e l e t o n f a l l s 2 mm and  i n f i l t r a t i o n o c c u r s a t a l l , the subsequent drop o f the a l u m i n a i n d i c a t o r can  be d e t e c t e d and measured. measure  the:riseof  infiltrant  Since the motion o f the i n d i c a t o r does not d i r e c t l y  the l i q u i d i n t o t h e s k e l e t o n ,  an a n a l y s i s o f the f l o w of the  is- required.  The geometry  of the mold and s k e l e t o n i s shown i n F i g u r e 7" and i t can  be seen t h a t the d i a m e t e r o f the carbon mold c a v i t y the  immediately a f t e r  s k e l e t o n i s 0.315"*  i s 0.329" where as t h a t o f  Hence the a r e a of the a n n u l a r space between the s k e l e t o n  2 and the mold i s o n l y 0..00707 i n . .  The volume f o r a l " l e n g t h o f annulus i s  3 0.00707 i n . .  The volume of the i n f i l t r a n t used was j u s t  e q u a l t o the pore v o l -  ume o f the s k e l e t o n , u s u a l l y about 0.061 i n . . Hence i f the a n n u l a r space i s completely f i l l e d  i t would r e q u i r e o n l y 11.5$ o f the t o t a l  available  liquid."  We can c o n s i d e r the a n n u l a r r e g i o n as a c a p i l l a r y w i t h w a l l s c o n s i s t i n g o f carbon and n i c k e l . be a n e g a t i v e  S i n c e carbon i s n o t wetted b y the l i q u i d m e t a l c a p i l l a r y pressure  annular r e g i o n .  (9 > 9 0 ° ) t h e r e  s e t up which w i l l oppose t h e f i l l i n g  will  of t h i s  Hence the amount o f l i q u i d which e n t e r s t h e annulus and which  can be c o n s i d e r e d n o n - i n f i l t r a t e d w i l l be l e s s t h a n the 11.5$ o f the t o t a l  infil-  trant.. I n c l u d i n g t h e above  -argument  alumina r o d drops w i l l be r e l a t e d the r a t i o  i t can be seen t h a t the d i s t a n c e  to the.height  of i n f i l t r a t e d l i q u i d  simply by  o f the a r e a o f the c a p i l l a r i e s t o the a r e a o f the mold c a v i t y .  sample c a l c u l a t i o n i s . g i v e n b e l o w . and hence a p o r o s i t y o f ^0$.  the . 1 " .  A  Specimen .9^ had a s k e l e t o n d e n s i t y o f 60.0$  I f the alumina i n d i c a t o r moved 0.5 cm then the  h  (cm  8.00 - H  7-00 - 4  ro C O  T  F i g u r e 8:  t 3  T  < t  7 (seconds)  H e i g h t of I n f i l t r a t i o n  vs.  35  Time f o r S o l i d N i c k e l Rod " I n f i l t r a t e d "  with  Silver.  - 29 l i q u i d had i n f i l t r a t e d 0.5 cm/0.4 = 1.2 cm into the skeleton.  In an attempt to  show the v a l i d i t y of the above argument a s o l i d n i c k e l rod was " i n f i l t r a t e d " i n the usual manner and a graph of indicator movement versus time i s shown i n Figure  8. Figure 9 shows the specimen a f t e r " i n f i l t r a t i o n " .  I t can be seen that  very l i t t l e s i l v e r flowed up the annular space.  Figure 9:  " I n f i l t r a t i o n " of S o l i d Nickel Rod with S i l v e r  - 30 b.  Rate E q u a t i o n s Rather than study the h e i g h t t o which l i q u i d r i s e s i n a porous  d u r i n g f i x e d time i n t e r v a l s study of the a c t u a l  as d i d Semlak and R h m e s  Ik  skeleton  , i t was f e l t t h a t  direct  r a t e of i n f i l t r a t i o n would be more u s e f u l t o a fundamental  u n d e r s t a n d i n g o f the p r o c e s s .  With t h i s i n mind a thorough a n a l y s i s o f the d i f - .  13 f e r e n t i a l e q u a t i o n f o r m u l a t e d by L i g e n z a and B e r n s t e i n t i o n 12 can be reduced dh =  #  LV  c  o  Equa-  to s  9  R  c  P&c  -  Vnh  dt  was c a r r i e d o u t .  8/*_  (16)  w i t h the assumptions made i n S e c t i o n A 6 and the' f u r t h e r assumptions t h a t the v i s c o s i t y and d e n s i t y of a i r are n e g l i g i b l e compared to those o f the l i q u i d m e t a l infiltrant.  The s o l u t i o n o f t h i s e q u a t i o n can .be shown to be  t =  2/>ih jfa  2  ^ cos  9.R  +  3  3 / O R h f?u3  (TTLV  C  c  o  s  Q  )  C?)  y  1  Values o f the p h y s i c a l ' q u a n t i t i e s a p p e a r i n g i n e q u a t i o n 17 have been taken from the l i t e r a t u r e i n Table III  when they were not e x p e r i m e n t a l l y d e t e r m i n a b l e and these a p p e a r  f o r the NiAg  system..  TABLE  III  Values o f Parameters i n E q u a t i o n 17 Material  Parameter  Ag •  2.98x10  Ag • Ni-Ag-H  2  10 m i c r o n s k e l e t o n  "T^LV cos  9 R  c  l i q u i d Ag  Reference  Value  926  2  poises  ergs/cm  59  .98 -k  2.39x10  cm 2  9.26gm/cm  1  g  25  980 cm/sec  2  25 26  - 31 Using these values the time required f o r i n f i l t r a t i o n of s i l v e r into a porous skeleton 10 micron n i c k e l powder i n hydrogen to a height of k cm i s 2 t =  (2)(2.98)(10" )(16) sec + (926j(.9SH2.39x10-4;  3 (9.26)(98o)(l0 )(2.98xlO~ ) (925)(.98) 3  2  2  = k.kO  sec + .0l4sec  2  It can be seen that the second term i s n e g l i g i b l e compared to the f i r s t i n the above equation and hence t h i s equation reduces to 2/Tth cos 9 E  t =  2  '  C  (18)  or \ 1/2 h = / QLV  c o s  Q  R  c  t  I  J  2^  (19)  Using equation 19, equation l 6 becomes  jlh d  By setting  =  ' 7TLV  C O S  9  R  c  Qynjt  t  -  g c R  2  (20)  Q/*^  = 0, equation 20 can be solved to determine the time required  for the l i q u i d to a t t a i n i t s equilibrium height which corresponds to the ter^mination  of i n f i l t r a t i o n .  The r e s u l t i s then as follows  t =  L  -V/O  2  y  cos 9  g  j (21)  2  From the above equations one can obtain plots of dh/dt vs..time and vs.  particle size.  This i s done i n figures 10 and 11.  From these equations  and graphs one can determine the time required f o r the rate to decrease to any given value or determine the rate of i n f i l t r a t i o n ( d h / d t j a t any given time f o r any p a r t i c l e size.  - 32 -  O  -50+100 mesh R  -20+35 mesh R &  10 microns R  c  c  c  = 29-5 x 10"  = 78.5 x 10*  cm-  cm.  = 2.39 x 10*" "cm.  3 — t (seconds) Figure 11:  dh ^  vs t f o r R  c  = 2.39,  29-5 and 78-5 x 10'  em.  c.  Rate of I n f i l t r a t i o n Results In order to show the v a l i d i t y of Ligenza and Bernsteiris t h e o r e t i c a l 1  analysis plots of the height of i n f i l t r a t i o n versus the square root of time were made.  Prom these graphs, i f the curve proves l i n e a r , an experimental value  of the slope i s determinable which can then be compared to equation 19. r e t i c a l slope f o r these curves i s shown i n equation Slope =  Jh dt / 1  where the 2/^  _2_  =  / #LV  s  Q*c\  22. ^  J  TT y  2  <*  The theo-  (22)  correction i s f o r the non-linearity of the powder skeleton c a p i l -  l a r i e s as discussed previously. The r e s u l t s of experiments of t h i s type are given i n Table IV: where K  c  and Kg are the t h e o r e t i c a l l y calculated and experi-  mental slope values r e s p e c t i v e l y .  In Table IT., the clearance or size of the  annular space between the metal skeleton and the carbon mold i s given f o r each sample.  I t can be seen that the magnitude of t h i s clearance had a d i s t i n c t e f f e c t  on the experimental value of the rate. was  In a l l but one case when the clearance  large, the experimental rate of i n f i l t r a t i o n was much larger than that  t h e o r e t i c a l l y predicted. It i s f e l t that the i n i t i a l area through which i n f i l t r a t i o n occurs i s markedly affected by the size of t h i s annular region.  In a l l the experimentally  determined rates i t was assumed that i n f i l t r a t i o n Occured only through the end of the c y l i n d r i c a l skeleton. Hence the rate of depletion of the molten bath, which i s the experimentally measured parameter^ i s related t o the rate of i n f i l t r a t i o n of the l i q u i d into the skeleton simply by the r e l a t i v e areas of the end c y l i n d r i c a l skeleton, the area of the molten i n f i l t r a n t bath and the porosity of the skeleton.  I f the clearance i s increased the l i q u i d w i l l r i s e further up  the annulus as the negative c a p i l l a r y pressure w i l l be l e s s .  This w i l l cause  35  an increase i n the area through which i n f i l t r a t i o n can occur and hence the rate w i l l he larger than theoretically predicted* The f r i c t i o n between the carbon mold and the skeleton must also be considered when determining the rate of i n f i l t r a t i o n . annular space was sufficiently  It i s f e l t that when the  small then this friction may have caused periodic  "hanging-up" of the skeleton. Since a reading of the Indicator was taken every l/24th of a second, the hanging-up argument could explain the lover rates observed when the clearance was small. The horizontal regions i n Figure 12 are consistent with this .argument. 1/2  Other plots of the height of infiltration against t '  are shown i n  Figures 12, 13 and lk and although the corresponding calculated and experimental values of the slopes of these curves are not identical, agreement in several cases i s reasonably good. However i n a l l cases the plots were linear indicating that the height of i n f i l t r a t i o n i s proportional to t / as predicted by theory. 1  2  By graphical differentiation of plots of the height of Infiltration versus time i t was possible to obtain curves showing,the change i n rate of i n filtration  with time.  These curves are shown i n Figures 15 and 16 for two  different particle size skeletons. Also plotted on the same graphs are the theoretical predictions of the change i n rate of i n f i l t r a t i o n with time as given by equation 16.  The experimental curves do not coincide with the theore-  t i c a l predictions but both curves are of the same form. Hence i t can be seen from both theory and experiment that the rate of Infiltration decreases rapidly with time.  - 36 TABLE IV 1/2 Calculated and Experimental Slope Values of h Versus t ' Plots No.  Particle Size  Clearance Inches  Inf.  Ke cm/sec / 1  .69  2  KQ cm/sec  1.2  95  10 micron  .033  Ag  98  10 micron  .032  Ag  6.1  1.2  92  50 x 100  .023  Ag  6.3  4.2  102  50 x 100  .027  Ag  11.8  4.2  99  50 x 100  .010  Ag  1.9  4.2  100  20 x 35  .012  Ag  3.*  6.9  97  20 x 35  .015  Ag  2.8  6.9  94  20 x 35  .014  Ag  2.7  6.9  113  20 x 35  • 019  Cu  8.3  6.9  114  20 x 35  .019  Cu  818  6.9  110  20 x 35  .026  Cu  10.8  7.0  105  50 x 100  .014  Cu  4.7  h.3  109  10 micron  .038  Cu  13. h  1.2  106  20 x 35  .025  Pb  6.0  5.2  107  50 x 100  .030  Pb  12.5  3-2  112  50 x 100  .019  Pb  5.7  3.2  .  - 42 3.  Density Since the amount of l i q u i d metal, which flows by c a p i l l a r y action from  the l i q u i d bath into the channels of the skeleton, i s to a c e r t a i n extent a measure of i n f i l t r a t i o n i t was f e l t that end-point density, or density of the composite a f t e r i n f i l t r a t i o n , would be a useful parameter to investigate.  With  t h i s i n mind resultant densities were measured on most of the composites.  a.  Density Gradients Due to Uneven Deoxidation As outlined i n the procedure non-uniform.reduction of oxide on the  n i c k e l skeletons occurred i n e a r l i e r experiments, owing to the i n a b i l i t y of hydrogen to reach e f f e c t i v e l y the lower part of the skeletons. of composites produced i n the e a r l i e r work are given i n Table V.  The densities A substantial  amount of scatter i s evident both with lead and s i l v e r as the i n f i l t r a n t .  How-  ever the r e s u l t s appear to indicate higher densities with smaller p a r t i c l e sizes. There was less, reduc.tionofsurf ace oxide the further the n i c k e l was i n ^ i the mold cavity.  Several density d i s t r i b u t i o n measurements were taken by  sectioning an i n f i l t r a t e d c y l i n d r i c a l composite into ten l/2 cm high cylinders and measuring the density of each i n d i v i d u a l section.  The r e s u l t s of these ex-  periments are plotted i n Figure 17 and 18, from which i t can be seen that higher d e n s i t i e s were obtained at the top of the specimen even though i n f i l t r a t i o n occurred from the bottom.  This allows the statement of a q u a l i t a t i v e r e l a t i o n -  ship between density and oxide content.  Quantitative dependence, however, was  not determinable due to the extremely small percentages of oxide involved.  b.  S o l i d i f i c a t i o n Porosity Since the density of most l i q u i d metals i s less than that of t h e i r  s o l i d s a contraction upon s o l i d i f i c a t i o n occurs.  I f a moving s o l i d i f i c a t i o n  interface i s not planar and nucleation i s occurring ahead of the interface, then  - 1+3 TABLE V R e s u l t a n t D e n s i t y With Non-uniform D e o x i d a t i o n  No.  System  29 ,28 23 24 ,27  ..  44 39  38  32 31  30 26  25 ..22  36 .: 47 56  '59 60 •61 -62 65  66 68 69 73 76  '63 51  52 71  -14+20 N i + -14+20 N i + -20+35 N i + -20+35 N i + -20+35 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + lOmicronNi + -50+100 N i +  Pb Fb Pb ' Pb Pb Pb Fb Fb Fb Fb Pb Fb Pb Fb Fb Ag  -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i + -50+100 N i . + lOmicronNi'+ 10micronNt:+ lOmicronNi"+ lOmicronNi + lOmicronNi + lOmicronNi + -20+35 N i +  Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag . Ag Ag Ag Ag Ag Ag Ag  -50+100 N i + Ag  50  48 54 55 64 .. 70  Resultant Density  •  -20+35  -20+35  N i + Ag  N i + Ag  89."+$ 86.3$ 88.1$ 85.0^ 90.2$ .  92.7$  98.0$  92.5$ 83.5^ 76.0$  76.8$ 89.2$  90.5$ 95-5$ 99«0$ 79»2$  84.9$ 87.0$  80.8$ 77•8$ 92.3$ 96.3$ 80.0$  83.4$ 83.6$ 86.7$ 83.7$ 77.5$ 99*3$ 87.0$ 96.0$  86.5$ 90.0$  93*5$ 79-^$  . 78.8$ 85.I  - U6 liquid w i l l locally be prevented from flowing to the solidification shrinkage. In an infiltrated powder skeleton there are many semi-Isolated regions of liquid between particles and since the likelihood of the infiltrated metal solidifying at the particle neok Is high this type of porosity would be very likely i n such a composite.  Also, since the temperature gradient In the Infiltration furnace  was very low there would have been no tendency for solidification to occur at one end of the specimen and proceed i n the direction of the temperature gradient. Equation 23 gives the relationship between the resultant solidification  porosity  in an Infiltrated powder composite and the densities of the materials concerned. Porosity a P I 1 B  where  \  ^°1 1 |  ?OTs J  (23)  P„ = porosity of original skeleton / ^ i l  o density of infiltrant when liquid  /Ois  » density of infiltrant when solid  Table VI gives the ratio ^ ^ i l / ^ i s for some common Infiltrants, TABLE VI  (Pll/jOls Metal  for Various Metals  Temperature^^  /3ii//3is  Pb  4oo°c  .927  Ag  960.5°C  .887  Zn  l*00°C  .936  Cu  1083°C  - .885  Zn  Ul9°C  .971  - 1*7 -  In l a t e r e x p e r i m e n t s ,  the n i c k e l s k e l e t o n s  were h e l d above the carbon mold d i r e c t l y  i n the c e n t r e o f the hydrogen f l o w a l l o w i n g the r e d u c i n g gas to pass through a n d " around them.  Under these c o n d i t i o n s g r a d i e n t s  eliminated. If  the  D e n s i t i e s o b t a i n e d i n the  i n the r e s u l t a n t  l a t e r work are  d e n s i t y were  c o l l e c t e d in T a b l e V I I .  -50 +100 mesh n i c k e l d e n s i t y v a l u e s are t a k e n as an example,  resultant  96.1$;  d e n s i t y f o r the f o u r samples i s  i.e.  the average  the p o r o s i t y i s  3«9$«  S i n c e the o r i g i n a l p o r o s i t y of a -50 +100 mesh n i c k e l s i n t e r e d f o r one hour  900°C i s v e r y c l o s e t o the  and from T a b l e  Vl/Oil/^Ois  .887,  f o r s i l v e r equals"  s o l i d i f i c a t i o n p o r o s i t y can be c a l c u l a t e d from e q u a t i o n 23 as f o l l o w s  .38(1 - .887)  p • =  Similar calculations  =  .043 or 4.3$  can be performed f o r o t h e r  sembled i n T a b l e V I I I . by  38$  at  composites  The s o l i d i f i c a t i o n p o r o s i t y  and t h e s e are  as-  argument can be f o r t i f i e d  the f a c t t h a t copper i s known to i n f i l t r a t e c o m p l e t e l y i n t o i r o n p r o d u c i n g  densities  g r e a t e r than 99$  •  However, under the e x p e r i m e n t a l  work a p o r o s i t y o f 2.8$ r e s u l t s porosity.  agreement between the c a l c u l a t e d  of  this  which can o n l y be e x p l a i n e d as s o l i d i f i c a t i o n  I t must be s t r e s s e d t h a t the  a maximum which assumes a t o t a l  geometry  calculated  s o l i d i f i c a t i o n porosity  lack of feeding d u r i n g s o l i d i f i c a t i o n .  is  Whereas  s o l i d i f i c a t i o n p o r o s i t y and the o b s e r v e d p o r -  o s i t y i s q u i t e good i n s e v e r a l cases, t h e r e appears t o b e inmost c a s e s - a r e s i d u a l p o r o s i t y which cannot be e x p l a i n e d .  c.  Copper-Silver I n f i l t r a t i o n into I t was f e l t t h a t s i n c e  to a n o t h e r ,  surface  Iron energy p r o p e r t i e s  v a r y from one  some r e l a t i o n s h i p between w e t t i n g c h a r a c t e r i s t i c s or  the r e s u l t a n t  d e n s i t y c o u l d be f o r m u l a t e d .  However i t  75"LV  A N <  system ^  can be seen from T a b l e V I I  t h a t s i m i l a r d e n s i t i e s were o b t a i n e d f o r the d i f f e r e n t systems  investigated.  - 48 TABLE V I I R e s u l t a n t D e n s i t i e s Under Uniform D e o x i d a t i o n C o n d i t i o n s  No.  System  Resultant Density  91  it  m i c r o n Ni• + Ag  95-4^ $  95  10 m i c r o n Ni. + Ag  94.9 i  96  10 m i c r o n Ni. + Ag  96.9 1o  79  -50 + 100  N i + Ag  97.4 $  78  -50 + 100  N i + Ag  96.5 $  77  -50 + 100  N i + Ag  96.5  92  -50 + 100  N i + Ag  95-8 $  99  -50 + 100  N i + Ag  94.8 %  102  -50 + 100  N i + Ag  95-2 Io  103  -50 + 100  N i + Ag  95-9 $  80  -50 + 100  N i + Ag  96.5 $  94  -20 + 35  N i + Ag  89.9 i  97  -20 +35  100  -20 + 35  109  N i + Ag N i + Ag  10 m i c r o n N i + Cu  f  92.8 $ 99-3 $ 93.6 io  105  -50 +' 100  N i + Cu  96.7 $  113  -20 + 35  N i +Cu  9^.3 i>  114  -20 + 35  N i + Cu.  91.4 ^  110  -20 +35  112  -50 + 100  N i + Fb  93.3 i  107  -50 + 100  N i + Fb  96.7 i  81  -50 + 100  N i + Fb  97-1 io  106 108 104  N i + iCu  -20 + 35 N i . + Fb -10O + 150 Fe •+ Ag ' -100 + 105  Fe •+ Cu  ••  94.7 io  89.0 ^ No I n f i l t r a t i o n  97.2 i  ->9" TABLE V I I I Comparison of E x p e r i m e n t a l and T h e o r e t i c a l  No.  Mesh S i z e  Infiltrant  S  S o l i d i f i c a t i o n Porosity  P /O  1 1  si  Porosity• * Obs. Calc.  91  lOu  Ag  .45  .887  5-1  4.6  95  lOu  Ag  .45  .887  5.1  5.1  96  lOu  Ag.  .46  .887  5-2  3.1  101  lOu  Ag  .46  .887  5.2  3.9  9k  -20+35  Ag  .40  .887  ^.5  10.1  91  -20+35  Ag  .40  .887  4.5  7.2  100  -20+35  Ag  • .42  .887  k.5  0.7  109  lOu  Cu  -.49  .885  5.6  6.3  105  -50+100  Cu  • 38  .885  4.4  3-3  110  -20+35  Cu  • 43  .885  5.0  5-3  113  .' -20+35  Cu  .44  .885  5.1  5.7  114  -20+35  Cu  • .43  .885  5-0 .  8.6  81  -50+100  Pb  .40  .927  2.9  2.9  107  -50+100  Fb  .41  • 927  3-0  3.1  112  -50+100  Fb  • 39  .927  2.8.  6.7  106  -20+35  Pb  .42  • 927  3.1  11.0  Cu  • 42  .885  4-9  2.8  115'  -100+150Pe  - 50 The v a l u e s of cos 9 and  TS'LY  and  are  l e a d - n i c k e l systems  f o r the c o p p e r - n i c k e l , c o p p e r - i r o n , s i l v e r - n i c k e l ,  given i n Table IX.  TABLE IX Values of  ~tf  T T r  cos 9 f o r V a r i o u s Systems  #LV  System  . ,  "C^LVCOS <  9  ergs/cm  It  is difficult  Pb-Ni  450  28°  397  Ag-Ni  926  7°  918  Cu-Ni  ' 1280  6°  1260  Cu-Fe  1280  ikP  1240  Ag-Fe  926  36°  748  lie  •  tf  as t h a t f o r l e a d - n i c k e l .  i n a large- e r r o r  j^-cos  9 f o r s i l v e r - i r o n i s almost t w i c e  as  The o n l y p o s s i b l e e x p l a n a t i o n would appear  i n the c o n t a c t angle f o r the  under the e x p e r i m e n t a l c o n d i t i o n s i n t h i s work. acy t o which these a n g l e s were measured and the systems, t h i s  2  t o e x p l a i n the f a i l u r e of s i l v e r t o i n f i l t r a t e i n t o an i r o n  s k e l e t o n when the p r o d u c t o f large  ergs/cm  s i l v e r - i r o n system as However i n view of the  good agreement  w i t h the  to  measured accurother  seems u n l i k e l y .  S i n c e i t was found t h a t s i l v e r does not i n f i l t r a t e i n t o i r o n a t and. t h a t copper i n f i l t r a t e s extremely w e l l ,  i t was f e l t  t h a t a study o f  all  the  i n f i l t r a t i o n of s e v e r a l c o p p e r - s i l v e r l i q u i d a l l o y s i n t o i r o n would prove f r u i t ful./  Seven s i l v e r - c o p p e r a l l o y s were p r e p a r e d and i n f i l t r a t i o n was c a r r i e d  at a constant In  temperature  out  above the l i q u i d u s of the c o p p e r - s i l v e r phase diagram.  F i g u r e 19 the p e r c e n t a g e r e d u c t i o n i n the a s - s i n t e r e d  p l o t t e d as a f u n c t i o n of the weight p e r c e n t  skeleton porosity  is  copper i n the c o p p e r - s i l v e r a l l o y .  100-4  H  Wt. Figure 1 9 :  °lo Cu  Percent Reduction - i n . Skeleton P o r o s i t y  vs Copper Content i n Cu-Ag  Infiltrant  - 52 Since the c o p p e r - s i l v e r phase diagram i s a simple e u t e c t i c .with very  little  s o l i d s o l u b i l i t y o f the components i n one another at room temperature,  the  d e n s i t y of the s o l i d i f i e d i n f i l t r a n t was assumed t o v a r y l i n e a r l y between .densities  o f the pure  • It 19-  metals.  can-be  seen t h a t t h e r e a r e  three d i s t i n c t regions i n f i g u r e  From zero to 5$ copper t h e r e was no i n f i l t r a t i o n .  t h a t i f copper i s  surface  active  T h i s would i n d i c a t e  i n l i q u i d s i l v e r at a l l , i t  i s i n t h i s amount wetting  i n s u f f i c i e n t to promote a low v a l u e of conditions.  the  There i s a t r a n s i t i o n zone from 5$ t o a p p r o x i m a t e l y 28$ copper  where i n f i l t r a t i o n , a s measured by the percentage f i l l i n g o f the channels.undergoes a large i n c r e a s e .  skeleton  From  i n d e n s i t y i s much more g r a d u a l t e r m i n a t i n g i n a f i n a l d e n s i t y of pure copper i n t o an i r o n s k e l e t o n .  T h i s phenomenon can be a n a l y s e d on a semi-  q u a n t i t a t i v e b a s i s by comparing the w e t t a b i l i t y o f a l l o y s o f on i r o n s k e l e t o n s .  97'2$ f o r  copper-silver  The v a l u e s o f c o n t a c t angle o b t a i n e d f o r v a r i o u s  copper-  s i l v e r a l l o y s on Armco i r o n sheet are p l o t t e d i n f i g u r e 20 as a f u n c t i o n o f composition. constant 80$  at  From t h i s curve i t  o  can be seen t h a t the c o n t a c t angle i s f a i r l y  .  about 35 4 up t o 50$jCopper where i t drops t o a v a l u e o f 13  copper and i s assumed t o remain c o n s t a n t  appears t h a t t h i s i s somewhat c o n t r a d i c t o r y  t o 100$ c o p p e r . t o the r e s u l t s  At f i r s t  o  at  it  shown i n f i g u r e 20.  However, one must c o n s i d e r t h a t the d r i v i n g f o r c e f o r i n f i l t r a t i o n i s p r o p o r t i o n a l to  "7T r T  r  c  os  9 and not 9 a l o n e .  .Li V  With t h i s i n mind t h e . d a t a o f K r a u s e ,  *  16 Sauerwald and M i c h a l k e  f o r the s u r f a c e t e n s i o n o f s i l v e r - c o p p e r a l l o y s  1050°C was i n c o r p o r a t e d w i t h the c o n t a c t angle measurements. cos 9 i s c a l c u l a t e d i n T a b l e X and the r e s u l t s  at  The parameter  p l o t t e d i n f i g u r e 21.  TABLE'X *K l_Y cos 9 f o r the -Copper-Silver-Iron System f o r Various Copper Concentrations $ Cu  tf"  Ag-Cu  LV  16  cos 9  9  "tf*LV  C  O  S  9  Alloy  0  926  36.3  .805  750  10  930  35.5  .814  755  20  9U0  34.9  .820"  770  6o  1040  32.2  .854  890  80  1090  12.8  1.975  1060  100  1280  13.3  i.974  1245 ."  '  From the curve i n Figure 21 i t can be seen that below 20$ copper the product *$Ly cos 9 remains very low compared to the values f o r copper contents greater than 20$.  The low value of resultant density shown on Figure 19 can be at7f^  tributed to t h i s low value of  v  cos 9.  Above 20$ the values of  r i s e with increasing copper content to a maximum of 1245 This larger value of d.  "^f^y  c o s  9  "ETLV  C O S  f o r pure copper.  r e s u l t s i n a more dense composite.  E f f e c t of Temperature on Resultant Density of Lead-Nickel System; In several experiments  skeleton at various temperatures resultant density.  lead was i n f i l t r a t e d , into a porous n i c k e l to determine the e f f e c t of temperature  on  The results of t h i s study are plotted i n Figure 22 where  the resultant density of a composite of -50 +100 mesh n i c k e l i n f i l t r a t e d with lead i s shown as a function of i n f i l t r a t i o n temperature. appreciable scatter at the low temperatures decreases steadily with  temperature.  Although there i s  i t seems l i k e l y _ t h a t the density  9  t  aoo. q  70.0^  ,  I  4oo T  , F i g u r e 22:  -r 500  j 600  r  i  700  T (°C) ' D e n s i t y o f Lead I n f i l t r a t e d N i c k e l Composites vs Temperature  800 of  Infiltration  '  I 900  - 57 cos 9 as c r i t e r i o n f o r i n f i l t r a t i o n  If we use the product Li v  a simple, d i f f e r e n t i a t i o n with respect to temperature w i l l indicate the effect of temperature on i n f i l t r a t i o n . d #  L V  cos Q  =  cos 6  d  dt  d cos 9  +  dt  -tf  ^  LV  dt  In order to determine d cos 9/dt a series of contact angle measurements at various temperatures were performed f o r the lead-nickel system.  The r e s u l t s  of these experiments are shown i n figure 23 • From these results Figure 2k was plotted to show the r e l a t i o n s h i p d  c  o  s  9  dT  of 9-32 x I O  °C~  - 5  between cos 9 and temperature and a value of  was obtained. The value of d  1  L v  5  / d T f o r lead i s "  u  known to be - . 0 8 ergs/cm /°C and hence equation" 23 can be solved using average 2  values of cos 9 and  d  L V  C O S  =  9  dT  0 y L  of 0.91 and  (-.08)(.9l) +  = -2.95xl0"  2  475 ergs/cm  respectively.  (9.32xl0- /°C)(475)ergs/cm 5  2  ergs/cm /°C  Hence i t can be seen that the d r i v i n g force f o r i n f i l t r a t i o n should decrease —2 l i n e a r l y f o r the lead-nickel system at a rate of 2.95 x 10  2 o ergs/cm / C.  Q u a l i t a t i v e l y t h i s can be r e l a t e d to the l i n e a r decrease of resultant density f o r the lead-nickel system which i s plotted i n jFigure 22. k.  E f f e c t of Temperature on Height of C a p i l l a r y Rise The height of r i s e of a l i q u i d i n a c a p i l l a r y i s given by equation  10 and several calculated values are given i n Table XI f o r d i f f e r e n t systems. It can be seen from Table XI that the height of r i s e i s generally quite large and obtaining a uniform hot zone of t h i s length experimentally would be very difficult.  .  .800-4  i— 400  1  500  s  600  1  700  r  800  ">  900  T (°C) F i g u r e 24:  Cosine o f t h e Contact Angle f o r Lead N i c k e l System vs Temperature  - 60 -  TABLE XI Calculated Height of C a p i l l a r y Rise Using Equation 10 System ,  Skeleton Powder Size  Height (cm) at M.P. of L i q u i d  10 micron  '.. Ni-Pb Ni-Pb  -50+100 mesh  Ni-Pb  -20+35 mesh  Ni-Ag  10 micron  321 26.0 9.77 743  Ni-Ag  -50+100 mesh  60.2  Ni-Ag  -20+35 mesh  22.6  Ni-Cu  10 micron  Fe-Cu  : -50+100 mesh  1025 83.8  However, with the lead-nickel system these t h e o r e t i c a l l y predicted ~ heights were not achieved as i n the -50 +100 mesh skeleton the lead rose only approximately 4.0 cm. I t was also noted that as the temperature  of i n f i l t r a -  t i o n was increased t h i s height became less as shown i n Figure 25- Only a t very low temperatures,  20°C above the melting point of lead (327°C), d i d the lead  i n f i l t r a t e completely t o the top of the skeleton (5.0cm).  From Figure 25 the  experimental value of dh/dT i s found.to be -7*2 x 10"^ cm/°C.  The values of  the parameters i n equation 11 f o r -50 + 100 mesh n i c k e l I n f i l t r a t e d with lead are given i n Table XII.  The values are used t o calculate dh/dT r e s u l t i n g i n a  t h e o r e t i c a l value of 7.8 x 10 ^ cm/ C. G  The comparison between experimental and  t h e o r e t i c a l values i s not good but no explanation can be giVen. i s noted that both values of t h i s temperature i n d i c a t i n g that the temperature  However, i t  c o e f f i c i e n t are extremely small  o f . i n f i l t r a t i o n has l i t t l e e f f e c t on the height  of c a p i l l a r y r i s e . i n lead-nickel system.  - 62 TABLE XII Values of Parameters  i n Equation 11  Parameter  Value  Reference  d cos 9 dT  8.05xlO" /°C  F i g . 2k  -.o8ergs/cm /°C  Ref. 5  5  2  dT  d/O  Ref. 25  -1.2xlO" gms/cc/°C 3  dT 10.51  /Opb cps 9  5.,  Ref. 25  gms/cc  .883  F i g . 2k  455 ergs/cm  Ref. 5  Contact Angle The r e s u l t s of the s e s s i l e drop experiments are shown i n Table XIII  and i t may be noted that the agreement between the two methods f o r measuring contact angle i s quite good. a.  Silver-Copper Alloys on Iron Base Sheet. Sessile drop experiments were performed using l i q u i d silver-copper  a l l o y s on two types of i r o n base sheet, Armco i r o n and a Stelco rimmed lowcarbon s t e e l sheet.  The composition f o r the two substrates ' i s given i n  Table XIV.  TABLE XIV 'Composition of Armco Iron and Stelcc Low Carbon Steel Material  C  Mn  S  P  Armco 99-99 Fe  .012  . 01.7  .005  Stelco Low-C s t e e l  •07  •31  ;oio  .  .025 .025  TABLE X I I I R e s u l t s o f S e s s i l e Drop Experiments  No.  Liquid Phase  Solid Substrate  Ag Ag  Low-Carbon S t e e l Low-Carbon S t e e l Low-Carbon S t e e l Low-Carbon S t e e l Low-Carbon S t e e l LOw-Carbon S t e e l Low-Carbon S t e e l Low-Carbon S t e e l Nickel Nickel Nickel Nickel Nickel Armco I r o n Armco I r o n Armco I r o n Armco I r o n Armco I r o n Armco I r o n Armco I r o n Armco I r o n Low-Carbon S t e e l Armco I r o n  1  2  3 4  6 7 8 . 9 10 11  12 13. l4 15 16 .17 18 2021 22  23 2k . 25  95Ag  5Cu  9 0 A g lOCu 8 0 A g 20Cu 60Ag  40Cu  95Ag  5Cu  20Ag 80Cu 40Ag 60Cu Ag Ag Ag Cu Cu Ag 9 0 A g lOCu 80Ag 20Cu 6 0 A g 40Cu 40Ag. 6 0 C u 20Ag 8 0 C u Cu Cu Cu  Area cm^  "1.54 1.48 2.32 1.29 2.31 2.70 2.96 2.70 1.54 1.03 2.64 1.03 2.32 O.386 O.708 0.450 0.643 - 0.515 0.708 0.778 O.708 1.48 0.670  Weight gms.  h cm.  O.58I  .061 .071 .025 .074 .030  0.610 0.502 0.511 0.412 0.264 0.345 0.504 0.367 0.311 o.4oi 0.132 0.808 0.249 0.512 0.274 0.468 0.602 0.430 " 0.201  0.175 0.188  0.144  , . 020  .030 •035 .040 .065 • 035 .030 .080 .106 .135 .125 .140 . .200 .145  • 055 .063  .040  .065  B a s h f o r t h Adams 9 0  10.7 13'.1 5-6 13.8 4.8 2.5 3-0 4.9 7-5 10.5 • 3.6 5-8 10.4 38.8 32.4 35-0 35.5 61.7 30.5 13.1 13.1 4.7 •11.9'  .  Area .9°  9-9 11.7 3--2 13.2 4.0 2.5 3-5 4-3 6.5 12.9 4.3 .60 10.6 33-6 31.7 36.5 34.3 . 52.5 „ 34.0 12.7 15-1 6.6  16.0  1 ON 00  - 6k In a l l cases the contact angle between the copper-silver a l l o y s and the low-carbon s t e e l sheet, i n c l u d i n g pure copper and pure s i l v e r , was than with the purer Armco i r o n .  lower  Since both substrates were given the same pol-  i s h i n g and reducing treatment they were assumed to be similar with respect to surface oxide content and surface roughness.  Because of t h i s surface s i m i l a r -  i t y i t i s f e l t that the difference i n chemical composition of the two substrates could be the cause of the d i f f e r e n t contact angle values.  As can be seen from  Table "XDtVthe sulphur and phosphorous concentrations of the i r o n and low-carbon s t e e l are very s i m i l a r ^ i t seems u n l i k e l y that either of these two elements could be responsible f o r the marked change i n contact angle.  Even i f a s u l -  phide or phosphide formed at the interface i t i s d i f f i c u l t to see how would r e s u l t i n a decrease i n  T5"  ot  this  which i s required f o r improved wetting.  Sli  Since the copper-silver a l l o y s were prepared i n carbon molds at approximately 1050°C they were probably saturated with respect to carbon and any change i n the carbon content of the substrates would be u n l i k e l y to produce any change i n the carbon concentration of the l i q u i d or any change i n the surface energies i n v o l v e d .  The manganese content of the s t e e l i s approxi-  mately eighteen times that of the i r o n .  Since copper and manganese have a high  20 degree of s o l u b i l i t y  i t i s possible that a copper-manganese s o l u b i l i t y zone  forms at the l i q u i d - s t e e l interface which decreases contact angle.  _, and decreases the T  However, i t , i s impossible to state conclusively on the basis  of these few experiments that manganese i s the Origin of the lower contact angles obtained with the mild s t e e l as the substrate. b.  Contact Angles of S i l v e r on Nickel Sheet The contact angle between molten s i l v e r and s o l i d n i c k e l at 985°C  was found to vary from 12° to k° with time.  Experiments  i n which the drop  was kept molten f o r various times were c a r r i e d out with the r e s u l t s shown i n  - 66 Figure 26.  These r e s u l t s i n d i c a t e a d i f f u s i o n c o n t r o l l e d contact angle.  L i q u i d s i l v e r d i s s o l v e s about 0.5$ n i c k e l and s o l i d n i c k e l d i s s o l v e s about 3$ s i l v e r at 985°.  I n t h i s system/there are no i n t e r m e t a l l i c compounds formed.  Hence the s o l u t i o n of one metal i n the other provides the s o l i d - l i q u i d i n t e r face with an a l l o y e d l a y e r w i t h which there i s associated a lower surface energy between the s o l i d and the l i q u i d . i n a decrease of 9.  Hence  g L  i s decreased, r e s u l t i n g  I n i t i a l l y , l i q u i d state d i f f u s i o n causes a r a p i d rate of  decrease of 9 as the n i c k e l i s d i s o l v e d i n t o the l i q u i d s i l v e r .  Then s o l i d  state d i f f u s i o n of s i l v e r i n t o the n i c k e l begins t o become e f f e c t i v e .  Essent-  i a l l y we have two b u f f e r zones between the pure s i l v e r and the pure n i c k e l ; a s i l v e r - r i c h l i q u i d ; z o n e and a n i c k e l - r i c h s o l i d zone with the solutes being n i c k e l and s i l v e r r e s p e c t i v e l y . c.  C a l c u l a t i o n of  ^TsL  In order to c a l c u l a t e  T^gL  i t i s necessary to know or assume a  value of "TS'sV' A reasonable estimate o f iSsv ^ e m p i r i c a l r e l a t i o n s h i p ^ ^ ' g y is approximately 4/3 metals i s known.  obtained by using the  s  "O^LV' i s  n c e  "c^LV ^  o r  m  o  s  t  As the contact angles have been measured f o r the systems i n  t h i s work, s o l u t i o n of equation 1 w i l l y i e l d the corresponding values of ^SL,  which have been l i s t e d i n Table XV.  I t can be seen that i n general  the systems which show b e t t e r wetting have a lower value of ~&g^'  However,  that t h i s does not n e c e s s a r i l y apply to i n f i l t r a t i o n behaviour i s seen by comparing the l e a d - n i c k e l and i r o n - s i l v e r systems. value of ~^Qi t i  The former has a higher  but. i n f i l t r a t e s b e t t e r than the i r o n - s i l v e r system which i n  f a c t does n o t . i n f i l t r a t e at a l l .  These two systems a l s o do not obey the  o r i t e r i o n o u t l i n e d i n s e c t i o n A2 that the higher the b e t t e r i s the i n f i l t r a t i o n .  c o s  © product the  - 67 TABLE XV Calculated Values of  System  "(5LV • Liquid  TTLV*  #SL  tfsv  9  7?SL  Cos 0  ergs/cm  Solid  Fe-Ag  926  1731  2300  36°  .806  1550  Cu-Ni  1280  i6ko  2190  6°  .99^  920  Cu-Fe  1280  1731  2300  3°  .998  1025  Fb-Ni  455  l6k0  2190  28°  .883  1788  Ni-Ag  926  I6k0  2190  6°  .994  1275  * Using  d.  T ^ Q T T  -,V3  " ^ L V  W  N  E  R  E  " ^ L V  v  a  l  u  e  s  a  r  e  obtained from Taylor**.  Secondary D i f f u s i o n In the pure copper and copper-silver a l l o y s a secondary d i f f u s i o n  band occurred that was noticable at the periphery of the drop.  In some cases  t h i s band was quite large having a diameter of 1 l/2 times that of the molten  23 drop.  This type of d i f f u s i o n band has been observed before.  and could sub-  s t a n t i a l l y e f f e c t the wetting c h a r a c t e r i s t i c s of the system i f i t were present before the drop attained i t s equilibrium shape.  However i t was observed that  drop equilibrium was attained before the d i f f u s i o n band appeared.  - 68 CONCLUSIONS 1.  The thermodynamic d r i v i n g force f o r i n f i l t r a t i o n i s " t f ^ y cos 0.  2.  In skeletons made from coarse powders (-50+100;mesh) the  portion of the skeleton i s completely i s used.  dense "even when i n s u f f i c i e n t  infiltrated infiltrant  In f i n e r (10 micron) skeletons when i n s u f f i c i e n t i n f i l t r a n t , i s used  complete density i s not attained and the i n f i l t r a t i o n interface is' not well defined.  3»  Tlie resultant density of an i n f i l t r a t e d compact depends d i r e c t l y  upon the amount of previous deoxidation of the skeleton and also the s o l i d i f i c a t i o n porosity r e s u l t i n g from the difference i n density between the and l i q u i d  k.  solid  infiltrant.  The i n f i l t r a t i o n of l i q u i d silver-copper a l l o y s into an i r o n skeleton  i s favoured by higher copper content of the i n f i l t r a n t .  This can be r e l a t e d  t o the increase InT^LV  The contact angle  0 0 8  ® with copper concentration.  between the copper-silver a l l o y s and low carbon s t e e l i s lower than that between the same a l l o y s and Armco i r o n . 5.  With the lead-nickel system i n f i l t r a t i o n i s more favourable at  lower temperatures. 6.  The height of the i n f i l t r a t i o n column i s d i r e c t l y proportional  to the square root of the time of i n f i l t r a t i o n .  The i n f i l t r a t i o n  process  occurs very rapidly^the time to i n f i l t r a t e a porous skeleton 5 cm long being l e s s than 0.3  7»  sec. f o r coarse powder skeletons.  The rate of i n f i l t r a t i o n  (dh/dt^varies with time, decreasing  r a p i d l y i n the i n i t i a l stages of i n f i l t r a t i o n .  - 69 -  BIBLIOGRAPHY 1.  Lenel, F. V., Private  2.  Bailey, G. L. J and Watkins, H. C , J . Inst. Metals, §0 ( 2 ) , 57 (1951/52)  3.  Graft, W. H., Fisher, J . I. and Schwartzbart, H., A. R. F. Project No..2765 (1961).  communications..  4., Tamman, G. and Rubenbeck, A., Z. Anorg, Allgem. Chem. 233, 192 (1935) 5.  Taylor, J. W., Progress i n Nuclear Energy, Series V, Metallurgy and Fuels, II, 398, (1959).  6.  Inman, M. C , and Tipler, H. R., Metallurgical Reviews, 8, No. 30 105, (1963).  7.  Taylor, J. W., Metallurgia, 5.0, l 6 l (1955).  8.  Van Vlack, L. H., J . Metals  9.  Kimura, T., Planseeberichte fur Pulvermetallurgie, 7_, 50, (1959).  251, (1951).  10.  Wenzel, P. R.,  Ind. aatt. Eng. Chem, 28, 988, (1936).  11.  Hayward, E. R., and Greenough, A. P., J . Inst. Metals, 88, 217 (1959/60).  12.  Schwartzkopf, P., Symposium on Powder Metallurgy, Iron and Steel Institute, 55, (1954).  13.  Ligenza, J . P. and Bernstein, R. B., J . American Chem. Soc,  4636,  (1951).  14. 15.  Semlak, K. A. and Rhines, F. N., Trans AIME, 212, 325, (1958), :Goetzel, C., Private  communication.  • .  Z  16.  Krause, W., Chem., 181,  17.  Bircumshaw, L. L., Phil. Mag. 2, 34l,  18.  Ellefson, D., and Taylor, J . W., J . Am, Cer. Soc. 21', (6) 205, (1938).  19.  ASM Handbook, l l 8 l (1948).  20.  ASM Handbook, II98 (1948).  21.  ASM Handbook, 1151  22.  Taylor, J . W., J . Inst. Metals, 86, 456, (1957/58).  23.  Bredzs, N. and Schwartzbart, H., Welding Journal, 4l-S  Saurewald, F., and Michalke, M., S B * * ® * * , 353, (1929).  anorg. u allgem  (1926),  (19^8).  1  140 (1962).  - 70 Bibliography  Continued  2k.  Gurland, J . Powder Metallurgy i n the Nuclear Age, 512, Metallwerk Plansee AG., Rftutte/Tyrol, (i.962).  25.  L i q u i d Metals Handbook, AEC, Dept. o f the Navy, Washington D. C. kO, (195 +). )  26. Handbook Of Chemistry and Physics, 27.  Buttner, F. H., J . Phys. Chem, ^6,  li-g'^&M),  657, (1952).  3068,(1960/61).  APPENDIX I 1.  E s t i m a t i o n of E r r o r i n C a l c u l a t e d Resultant Density a.  E r r o r i n density of s i n t e r e d  /O  =  ln^o = I n W - 2 I n D - I n 1  or  w  differentiating,  let  Nickel  AyO = e r r o r i n ^ O  .02 gms  W=  10 gms  A D  .002 i n .  D =  .325 i n .  A  D  A W error i n W etc.  ;  AW = =  2 A D  A W W  1 = .01 i n .  1 =1.7 i n -  p = 0.60 therefore  = -02 _ 2(.002) 10 .325  A p  = .6(.002 - .012 - .006) = .0096  b.  .01 1.7  o r 1$  Error i n Infiltrated  /Ocomp. = P +  Composite  w V  /°Ni  P  >°A, ^ A a  Where = density of sintered W  = weight o f  composite  V  = volume of  composite  liyOcomp. = In- P  +  W v  yO  A g  nickel  /°Ni  1  /OAg  J  P  A 1  A / O comp.  P  =A1  W  +  L  /Ocomp.  V  +  -+  /°Ag  w  /OAg  -  v/ ° A g  / ° N i  P  J  Pm  p  /OAg  l /°AgJ  L  v  /0  AS  .96  let  B =  B =  W V/OAg  = '  20  A W -  .87  -  W  C=  1  20  212  pP.Wi  =  . 6 (8.90)  •5  1  Hence  V=  r ^p +  L  .51  Since  /OAg  V  '.87 r.ooi -  let  = .87  (2.2X10.5)  TT D  2  0  J  =.51  -  P> N i  P  £^1 +  - 0"]  +  oJ  APAg I ...  /O Ag  J  =.0082.  1  A V= V  2 A D •+ A 1 D 1  ^ B =  .87  = 2(.00l) •+ .003 .325 1-7  (.00005 - .00791) =  «0069  =  .0079  Since  ^^comp. comp.  i s approximately •  =  Hence e r r o r  .OO87 =  .87$  1.00  APPENDIX I I  1.  Derivation of Formula f o r Contact Angle from Volume of Drop  Volume of a spherical segment i s : V = 1 TT h  2  (3r - h)  3 where  r  =  radius of sphere  h  = height of segment  2  and from the above figure  rj_  r  2  2  =  r  =  2rh - h  =  r  - ( r - h)  i  2  +  2h 2 Hence  V = ITT h  5  2  (3  T  l  2 *  2h  h  - h) =  .  1 JT  6  h  i&i  +  75  Since  r ^ i s greater than h 2  then  i s much greater than h  V = 1  tr  "but  h = r tan 9/2  r  2 2 3 r , - 1 TT h r . 1 -x 1  h  ir  V = 1  r  tr r ^  or  r  3 t a n  /  2  1  = Area  2  -  Hence  V =  Hence  _W_ = 1 p 2 or  e  r  2 but  2  I  of drop  = A  A V"  = W /O  weight of drop density  v 3/2  fT /AreaN  tan 9/2  ^ T I - ;  =  3_i5_5 W /OA37  2  , tan 9/2  

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