Multiphase diffusion in ternary Cu-Zn-Ni alloys
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T H E development of n o n p l a n a r i n t e r f a c e m o r p h o l o gies in a m u l t i c o m p o n e n t diffusion s y s t e m is a c o m mon m e t a l l u r g i c a l o c c u r r e n c e . I r r e g u l a r and nonp l a n a r m o r p h o l o g i e s have b e e n o b s e r v e d d u r i n g the growth of oxide s c a l e s and s u b s c a l e s on a l l o y s and in i s o t h e r m a l phase t r a n s f o r m a t i o n s in m e t a l l i c s y s t e m s . T h e s e m o r p h o l o g i e s r e f l e c t i s o t h e r m a l diffus i o n a l i n s t a b i l i t i e s that can a r i s e in m u l t i p h a s e diffusion. The kinetic and t h e r m o d y n a m i c c r i t e r i a u n d e r l y i n g this phenomenon a r e s t i l l to be explored. Howe v e r , such a n a l y s i s is e s s e n t i a l in the d e v e l o p m e n t and c o n t r o l of v a r i o u s m e t a l l u r g i c a l p r o c e s s e s like g a l v a n i z i n g , c a r b u r i z i n g , and n i t r i d i n g of s t e e l s , diffusion bonding, and cladding of m u l t i c o m p o n e n t a l l o y s . At p r e s e n t , v e r y little s y s t e m a t i c study has b e e n made of this p h e n o m e n o n , even in the s i m p l e s t of m u l t i c o m p o n e n t s y s t e m s , the t e r n a r y s y s t e m . One of the e a r l y s t u d i e s was by C l a r k and R h i n e s , 1 who i n v e s t i gated m u l t i p h a s e diffusion in the A 1 - M g - Z n s y s t e m at 335~ with sandwich couples and q u a l i t a t i v e l y studied the d e v e l o p m e n t of p h a s e s in the diffusion zone by m e t a l l o g r a p h i c t e c h n i q u e s . An a t t e m p t was made by these a u t h o r s to r e l a t e the phase z o n e s that d e v e l oped in the couples to the diffusion path q u a l i t a t i v e l y d e s c r i b e d on a t e r n a r y i s o t h e r m . K i r k a l d y and cow o r k e r s 2-4 developed the concept of a v i r t u a l diffusion path in an a t t e m p t to p r e d i c t the o c c u r r e n c e of diff u s i o n a l i n s t a b i l i t i e s in t e r n a r y s y s t e m s of C u - Z n - S n and F e - N i - C r . In this study m u l t i p h a s e diffusion in the t e r n a r y CuZ n - N i s y s t e m was i n v e s t i g a t e d at 775~ with sandwich couples set up with d i s k s of a ~ phase (bcc) alloy joined to pure copper or nickel d i s k s (fcc). The p u r pose of this r e s e a r c h was to study the d e v e l o p m e n t of n o n p l a n a r i n t e r f a c e s and r e c o r d the evolution of the diffusion s t r u c t u r e with diffusion t i m e . The m u l t i p h a s e z o n e s o b s e r v e d in the couples were r e l a t e d to the diffuC. W. TAYLOR, Jr., formerly at School of Materials Science and MetallurgicalEngineering,Purdue University, Lafayette, Ind., is currently 2rid Lt. U.S. Army Ordance Corps, Washhagton, D.C.M.A. DAYANANDA and R. E. GRACE are Assistant Professor and Head, respectively, School of Materials Science and MetallurgicalEngineering. Manuscript submitted September 18, 1969. METALLURGICA
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