Effect of grain size on the thermal diffusion of copper in aluminum
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S t a r k ~ have r e c e n t l y o b s e r v e d a s t r o n g g r a i n s i z e d e p e n d e n c e in the h e a t of t r a n s p o r t for s e l f - t h e r m a l diffusion in a l u m i n u m . T h e y find the h e a t of t r a n s p o r t f o r l a r g e and s m a l l g r a i n e d s a m p l e s to be +11 and - 2 k c a l / m o l e . On the b a s i s of the m a g n i t u d e s of the p h e n o m e n o n i n v o l v e d , they w e r e able to e x c l u d e the following f a c t o r s a s m a j o r c o n t r i b u t i o n s to t h e i r d i l a t i o n r e s u l t s : a) a h e a t of t r a n s p o r t in the g r a i n b o u n d a r y which is o p p o s i t e to that in the l a t t i c e , b) g r a i n b o u n d a r y inhibition to d i s l o c a t i o n c l i m b , c) the g r a i n b o u n d a r i e s a s s o u r c e s f o r an o v e r e q u i l i b r t u m v a c a n c y c o n c e n t r a tion g r a d i e n t which c a n c e l s the e f f e c t of an e q u i l i b r i u m v a c a n c y c o n c e n t r a t i o n in the s i n g l e c r y s t a l s , and d) d e n s i t y c h a n g e s . A s a r e s u l t of the e x c l u s i o n of t h e s e f a c t o r s , they p r o p o s e a n o n e q u i l i b r i u m c o n c e n t r a t i o n of v a c a n c i e s would a l t e r the k i n e t i c t h e o r y v a l u e of the h e a t of t r a n s p o r t f o r s i n g l e c r y s t a l s and be c o n s i s t e n t with t h e i r r e s u l t s . If t h e i r i n t e r p r e t a t i o n of those d a t a w e r e c o r r e c t , one would e x p e c t a g r a i n s i z e d e p e n d e n c e f o r s u b s t i t u t i o n a l s o l u t e t h e r m a l diffusion in a l u m i n u m c a u s e d by a n o n e q u i l i b r i u m d i s t r i b u t i o n of v a c a n c i e s . The p r e s e n t e x p e r i m e n t s w e r e c o n d u c t e d to i n v e s t i g a t e this p o s s i b i l i t y . In a r e c e n t a r t i c l e by O r i a n i , 3 a t a b u l a t i o n of s o l u t e h e a t s of t r a n s p o r t i s p r e s e n t e d . It a p p e a r s that the t h e r m a l diffusion of c o p p e r in a l u m i n u m h a s not b e e n s t u d i e d . C o n s e q u e n t l y , we have s e l e c t e d this s y s t e m . E X P E R I M E N T A L TECHNIQUE A m o d i f i c a t i o n of the t h e r m a l d i f f u s i o n f u r n a c e d e s c r i b e d in Ref. 1 w a s c o n s t r u c t e d to p e r m i t an i n c r e a s e d t e m p e r a t u r e g r a d i e n t . The g e o m e t r y of the s p e c i m e n s in the f u r n a c e r e m a i n s unchanged, and l a r g e and s m a l l - g r a i n e d s a m p l e s w e r e r u n s i m u l t a n e o u s l y . The s p e c i m e n s w e r e p r e p a r e d R. E. DOERR, formerly Graduate Student, Department of Mechanical Engineering, University of Texas at Austin, Austin, Tex., is now with Tracor, Inc., Austin, Tex. J. P. STARK is Associate Professor of Mechanical Engineering at the University of Texas at Austin. Manuscript submitted August 26, 1971. METALLURGICAL TRANSACTIONS
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