Interdiffusion in copper-rich cu-ag solid solutions
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C O P P E R and copper a l l o y s c o n t a i n i n g s i l v e r have b e c o m e of g e n e r a l i n t e r e s t in p r a c t i c a l u s e . F u n d a m e n t a l p h y s i c a l p r o p e r t i e s , however, have not be en a c c u m u l a t e d enough for u n d e r s t a n d i n g p h y s c o m e t a l l u r gical b e h a v i o r s of these m a t e r i a l s . Diffusion c h a r a c t e r i s t i c s in c o p p e r - b a s e solid s o l u t i o n s of the Cu-Ag s y s t e m have b e e n r e p o r t e d by s e v e r a l i n v e s t i g a t o r s : t r a c e r diffusion of Ag 11~ in p u r e copper,l-a in copper containing s m a l l a m o u n t of Ag and of C r , T e , Ti, or z r , a g r a i n - b o u n d a r y diffusion of Ag 1.~ in copper containing s m a l l amount of i m p u r i t i e s , 3 i n t e r d i f f u s i o n in C u - A g a l l o y s , z'4 and in A u - A g - C u ternary alloys, s Although i m p u r i t y diffusion of Ag n ~ in p u r e copper is well d e t e r m i n e d , diffusion data in s i l v e r - b e a r i n g copper a r e not enough for d i s c u s s i n g the b e h a v i o r of the m a t e r i a l s in the t e m p e r a t u r e r a n g e w h e r e they a r e put to p r a c t i c a l u s e . All m e a s u r e m e n t s in the a l l o y s w e r e done in a r e l a t i v e l y n a r r o w r a n g e of t e m p e r a t u r e and the effects of s i l v e r content on the diffusion have not been s e t t l e d yet. In the p r e s e n t study i n t e r d i f f u s i o n b e h a v i o r in c o p p e r - b a s e solid s o l u t i o n s c o n t a i n i n g up to 2.1 at. pct Ag was i n v e s t i g a t e d in the t e m p e r a t u r e r a n g e f r o m 974 to 1273 K, using conventional s a n d w i c h - t y p e diffusion couples and an e l e c t r o n p r o b e m i c r o a n a l y z e r . EXPERIMENTAL
K i r k e n d a l l shift of m a r k e r s was also studied at 1174 K u s i n g a l u m i n a p a r t i c l e s of 0.06 ~tm in d i a m . a s the m a r k e r . INTERDIFFUSION C O E F F I C I E N T S The value of D i n the t e m p e r a t u r e r a n g e between 974 and 1273 K was d e t e r m i n e d a s a function of the c o m p o s i t i o n ; the r e s u l t s a r e shown in Table II. Some e x a m p l e s of the c o n c e n t r a t i o n dependence of ~J a r e shown in Fig. 1. In the figure also shown a r e some data given by B a r r e a u et al., z who d e t e r m i n e d ~J in the t e m p e r a t u r e r a n g e 818 to 1043 K, using diffusion couples c o n s i s t i n g of p u r e copper and p u r e s i l v e r . P r e s e n t r e s u l t s show a slight i n c r e a s e in D with i n c r e a s i n g the a t o m i c f r a c t i o n of s i l v e r , NAg , while r e s u l t s given by B a r r e a u et al. show a d e c r e a s e . In t h e i r s p e c i m e n s a phase i n t e r f a c e between c o p p e r - b a s e t e r m i n a l solid solution and s i l v e r - b a s e t e r m i n a l solid solution e x i s t e d in the diffusion path. Such a phase irlterface u s u a l l y a c t s a s a b a r r i e r to the
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