Diffusion of zinc in the lamellar eutectic, Al-CuAl 2
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C O N T R O L L E D e u t e c t i c s have i n h e r e n t a d v a n t a g e s over other c o m p o s i t e m a t e r i a l s p r i m a r i l y b e c a u s e of t h e i r e a s e of f a b r i c a t i o n and t h e i r s u p e r i o r i n t e r f a c e s t r e n g t h . However, one of the m a j o r p r o b l e m s in u s i n g t h e s e m a t e r i a l s is in j o i n i n g them to the total s y s t e m without a l t e r i n g the eutecttc a l i g n m e n t . A p o s s i b l e method of j o i n i n g is solid state bonding. F o r example, high i n t e g r i t y bonds of eutectic to e u t e c t l c (A1-AlsNi) have been p r o d u c e d by diffusion at high t e m p e r a t u r e s and p r e s s u r e s . 1 The p r e s e n t study c o n s i d e r s the m o r e c o m p l i c a t e d s i t u a t i o n of diffusion b e t w e e n a c o n t r o l l e d b i n a r y eutecttc and a n o t h e r m a t e r i a l , in this c a s e a t h i r d e l e m e n t . D u r i n g this type of diffusion bonding, c o n c e n t r a t i o n g r a d i e n t s develop b e t w e e n the t h i r d e l e m e n t and each of the two eutectlc p h a s e s . F u r t h e r m o r e , a s the t h i r d e l e m e n t diffuses into each p h a s e t h e r e m a y be c o m p o s i t i o n a l a d j u s t m e n t s at the b o u n d a r i e s s e p a r a t i n g the two eutectic p h a s e s . T h e s e a d j u s t m e n t s m a y be n e c e s s a r y in o r d e r to m a i n t a i n i n t e r facial equilibrium. Finally, equilibrium requirements m a y c a u s e one o r m o r e new p h a s e s to f o r m . The o b j e c t i v e s of this r e s e a r c h w e r e to i n v e s t i g a t e these f a c t o r s in a model s y s t e m and to m e a s u r e t h e i r effects so that a f i r m foundation c a n be laid for diffusion bonding of c o n t r o l l e d e u t e c t l c s to o t h e r m a t e r i a l s . To achieve these o b j e c t i v e s Zn was bonded to and diffused into the c o n t r o l l e d l a m e l t a r A1-CuAla eutectic. Fig. 1 shows the A 1 - C u - Z n t e r n a r y at 200, 240, and 300oc. The s o l u b i l i t y of Zn in A1 v a r i e s s t r o n g l y with t e m p e r a t u r e , but the s o l u b i l i t y of Zn in 0 CuA12 is n e a r l y the s a m e ( ~ 1 wt pct) at each of the t h r e e t e m p e r a t u r e s . The p h a s e s ~ A1 and ~ Zn c a n c o e x i s t in e q u i l i b r i u m o v e r a l a r g e r a n g e of t e m p e r a t u r e s . 2 On the other hand, 0 CuA12 and ~ Zn cannot c o e x i s t in e q u i l i b r i u m (Fig. 1). a T h e r e f o r e , diffusion bonding of Zn and 0 will p r o d u c e a new phase at the 0 - ~ i n t e r face.4 M. R. JACKSONis Research Metallurgist, General Electric Research and Development Center, Schenectady, N. Y. J. I. GOLDSTEINand R. W. KRAFT are Associate Professor and Professor, respectively, Department of Metallurgyand Materials Science, Lehigh University, Bethlehem, Pa. This paper is based upon a thesis submitted by M. R. Jackson in partial fulfillment of the requirements of the degree of Doctor of Philosoph
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