Diffusion structures in multiphase Cu-Ni-Zn couples
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SISSON, J R . AND M. A. DAYANANDA
I s o t h e r m a l , m u l t i p h a s e diffusion w a s i n v e s t i g a t e d with infinite diffusion c o u p l e s in the C u N i - Z n s y s t e m at 775~ T h e c o u p l e s w e r e a s s e m b l e d with d i s k s of a/3 (bcc) t e r n a r y a l l o y s a n d w i c h e d b e t w e e n d i s k s of s e l e c t e d b i n a r y , C u - N i a (fcc) a l l o y s and w e r e a n n e a l e d f o r 2 h r to 2 d a y s . T h e diffusion s t r u c t u r e s w e r e i n v e s t i g a t e d m e t a l l o g r a p h i c a l l y and by e l e c t r o n p r o b e a n a l y s i s . T h e c o u p l e s d e v e l o p e d m u l t i p h a s e s t r u c t u r e s that showed t r a n s i t i o n s f r o m p l a n a r i n t e r f a c e s to n o n p l a n a r m o r p h o l o g i e s with c h a n g e s in c o m p o s i t i o n of the ( ~ - t e r m i n a l a l l o y s . The v a r i o u s s t r u c t u r e s a r e d e s c r i b e d by the a i d of c o m p o s i t i o n p a t h s . T h e v e l o c i t y of p l a n a r i n t e r f a c e s i s d i s c u s s e d in t e r m s of i n t r i n s i c f l u x e s in t h e a d j a c e n t p h a s e s . T H E d e v e l o p m e n t of diffusion s t r u c t u r e s in m u l t i p h a s e , m u l t i c o m p o n e n t a l l o y s p r e s e n t s m a n y f e a t u r e s of m e t a l l u r g i c a l i n t e r e s t f o r study. One of t h e s e f e a t u r e s i s t h e m o r p h o l o g y of i n t e r f a c e s b e t w e e n diffusion l a y e r s . I n t e r f a c e s can be p l a n a r o r n o n p l a n a r and a f f e c t not only the growth of l a y e r s but a l s o the evolution 'of diffusion structure. Diffusion s t r u c t u r e s d i s p l a y i n g n o n p l a n a r m o r p h o l o g i e s have been d e v e l o p e d by i s o t h e r m a l diffusion of m u l t i p h a s e c o u p l e s in t h e Cu-Zn-Sn,* F e - C r - N i , 2 and C u - Z n - N i 3 s y s t e m s . Such s t u d i e s have shown that the s t a b i l i t y of p l a n a r i n t e r f a c e s i s dependent on the t e r m i n a l c o m p o s i t i o n s of the c o u p l e s . T a y l o r e t al. a s t u d i e d m u l t i p h a s e diffusion in the C u N i - Z n s y s t e m at 775~ with d i s k s of a/3 (bcc) t e r n a r y a l l o y j o i n e d to d i s k s of p u r e c o p p e r o r n i c k e l (fcc) and o b s e r v e d the d e v e l o p m e n t of diffusion s t r u c t u r e s with t w o - p h a s e l a y e r s and n o n p l a n a r i n t e r f a c e s . In t h i s study m u l t i p h a s e diffusion in the C u - N i - Z n s y s t e m i s f u r t h e r i n v e s t i g a t e d a~ 775~ with s o l i d - s o l i d c o u p l e s in o r d e r to r e c o r d the v a r i a t i o n in diffusion s t r u c t u r e a s one of the two t e r m i n a l c o m p o s i t i o n s of t h e c o u p l e s i s v a r i e d . T h e s e c o u p l e s a r e a s s e m b l e d with d i s k s of a t3 (bcc) t e r n a r y a l l o y j o i n e d to d i s k s of a s e r i e s of (fcc) C u - N i b i n a r y a l l o y s of s e l e c t e
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