Interdiffusion in Co-Mn alloys
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mol-1/RT) m2/s,
and DMn = 0.98 x 10-4 exp (-229 kJ
mol-1/RT) m 2 / s .
IN
the past few decades, much efforts have been made on the t h e o r e t i c a l and e x p e r i m e n t a l s t u d i e s on diffusion in p u r e m e t a l s and dilute alloys.1 Although a few s t u d i e s on a t o m i c m e c h a n i s m of diffusion in conc e n t r a t e d a l l o y s have been c a r r i e d out, they a r e l i m i t e d to e i t h e r completely r a n d o m or c o m p l e t e l y o r d e r e d alloys .2 It may be i n t e r e s t i n g to study the diffusion p a r t i c u l a r l y in c o n c e n t r a t e d alloys to exa m i n e the r e l a t i o n s h i p s between the diffusion p a r a m e t e r s and t h e i r p h y s i c a l or t h e r m o d y n a m i c a l p r o p e r t i e s . The a c t i v a t i o n e n e r g y and f r e q u e n c y f a c t o r for i n t e r d i f f u s i o n d e t e r m i n e d by the A r r h e n i u s r e l a t i o n ship a r e r e l a t e d not only to the s e l f - d i f f u s i o n of both c o m p o n e n t s in the alloy but a l s o to the t e m p e r a t u r e dependence of the t h e r m o d y n a m i c f a c t o r in D a r k e n ' s r e l a t i o n . 3 F u r t h e r the effect of m a g n e t i c t r a n s f o r m a t i o n on the s e l f - d i f f u s i o n and i m p u r i t y diffusion has b e e n studied f a i r l y well in or-iron4-13 and cobait.14'15 Though, the p r e s e n t a u t h o r s have studied i n t e r d i f fusion in a s e r i e s of cobalt alloys, such as Co-Ni, 16 C o - P d 17 and C o - F e 18 alloys, now C o - M n s y s t e m has b e e n chosen for the i n v e s t i g a t i o n , s i n c e C o - M n alloys a p p e a r to be s u i t a b l e f o r s t u d y i n g both the t e m p e r a t u r e and c o n c e n t r a t i o n dependence of i n t e r d i f f u s i o n coefficient and the effect of m a g n e t i c t r a n s f o r m a t i o n on i n t e r d i f f u s i o n . T h i s has been f a c i l i t a t e d s i n c e cobalt and m a n g a n e s e f o r m a solid s o l u t i o n o v e r a wide r a n g e of t e m p e r a t u r e and c o m p o s i t i o n 19 (the m a x i m u m s o l u b i l i t y of m a n g a n e s e is about 58 pct* at *Compositionof alloysis expressedalwaysin at. pct unlessotherwisestated. 1433 K) and the m a g n e t i c t r a n s f o r m a t i o n takes place in an a p p r o p r i a t e t e m p e r a t u r e r a n g e for diffusion experiments. YOSHIAK1 I1JIMAand KEN-ICH1HIRANO are Instructor and Professor, respectively, Department of Materials Science, Faculty of Engineering, Tohoku University, Sendai, Japan. OSAMUTAGUCHI is Instructor, Miyagi College of Technology, Natori, Miyagi-Ken,Japan. Manuscript submitted December 6, 1976. METALLURGICALTRANSACTIONSA
In the p r e s e n t work, an a t t e m p t is also made to e x a m i n e the A r r h e n i u s r e l a t i o n s h i p s as cited above, in s o m e c o n c e n t r a t e d C o - M n a l l o y s . The i n t e r d i f fusion e x p e r i m e n t s on (pure C o ) - ( C o - 3 0 . 2 8 pct Mn alloy) and (pure
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