Diffusion-induced stresses and plastic deformation
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F a b r i c a t i o n of the Diffusion C o u p l e s
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ORIGINAL JOIN
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A - RICH B - RICH (b) Fig. 1--Schematic cross sections of A/B Kirkendall couples. (a) Typical nonbending, massive couple. (b) Bending, thinsheet couple. A, B and v are the binary metal components and vacancies, respectively. D = intrinsic diffusion coefficient, J = diffusion flux, and cr vectors indicate the sense of diffusion-induced stress.
and i n t e r c r y s t a l l i n e c r a c k i n g . 5,29'3~ If the d e g r e e of c o n s t r a i n t e x e r t e d by the ends of the couple is r e d u c e d s i g n i f i c a n t l y s i m p l y by m a k i n g a thin couple (20 to 200 pm in the d i f f u s i o n d i r e c t i o n ) , then the couple u n d e r goes m a c r o s c o p i c , p l a s t i c d e f o r m a t i o n (bending), the s i d e of the couple which i s r i c h e r in the f a s t e r - d i f f u s i n g c o m p o n e n t f o r m i n g the inner, concave s u r f a c e of the couple ( F i g . l(b)). B a r n e s 2 and Q u e i s s e r 13 a t t r i buted b e n d i n g of s o l i d / v a p o r c o u p l e s to d i f f u s i o n - i n d u c e d s t r e s s e s which, in the c a s e of Ni (solid)//Cu (vapor) c o u p l e s , 2 w e r e a s s u m e d to b e c a u s e d p r i n c i p a l l y by the a n n i h i l a t i o n and g e n e r a t i o n of v a c a n c i e s in the d i f f u s i o n zone but, in the c a s e of Si (solid)//B (vapor) c o u p l e s , I~ w e r e a t t r i b u t e d to high a t o m i c m i s fit. Liu and Powel112 have s u g g e s t e d that d i s l o c a t i o n c l i m b p a r a l l e l to the d i f f u s i o n d i r e c t i o n m a y c o n t r i bute to the b e n d i n g of thin A u / A g c o u p l e s . If s u c h i s the c a s e , then the a m o u n t of m a r k e r s h i f t should b e s m a l l e r than that o b s e r v e d in m a s s i v e c o u p l e s . Howe v e r , t h i s h y p o t h e s i s could not be t e s t e d b e c a u s e m e a s u r e m e n t s of the m a r k e r shift in thin c o u p l e s had not b e e n m a d e . The o b j e c t i v e s of t h i s i n v e s t i g a t i o n w e r e to s t u d y the d i f f u s i o n - i n d u c e d p l a s t i c d e f o r m a t i o n , m a r k e r shift, and m i c r o s t r u c t u r a l c h a n g e s in thin A u / A g coup l e s . In addition, an e l e m e n t a r y a n a l y s i s of the s t r e s s d i s t r i b u t i o n in thin couples was m a d e and an e s t i m a t e of the magnitude of the d i f f u s i o n - i n d u c e d s t r e s s e s was o b t a i n e d . T h e A u - A g s y s t e m was s e l e c t e d f o r t h i s r e s e a r c h b e c a u s e of the r e l a t i v e l y s m a l l a t o m i c m i s m a t c h and the abundance of a v a i l a b l e t e c h n i c a l and s c i e n t i f i c i n f o r m a t i o n on t h i s s y s t e m . 1532-VOLUME 8A, OCTOBER 1977
Gold and s i l v e r w i r e s (both 99.999 pct p u r e ) w e r e m e l t e d , c o l d - r o l l e d into s h
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