Growth temperatures in Al-CuAl 2 and Sn-Cd eutectic alloys
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THE
coupled zone concept is used f r e q u e n t l y to exp l a i n the s t r u c t u r a l f e a t u r e s of d i r e c t i o n a l l y solidified eutectic and o f f - e u t e c t i c c o m p o s i t i o n a l l o y s . Hitherto, such d i s c u s s i o n s have b e e n q u a l i t a t i v e r a t h e r than quantitative, p a r t i c u l a r l y in a n o m a l o u s eutectic s y s t e m s . 1 T h i s is due to a lack of a c c u r a t e growth t e m p e r a t u r e or u n d e r c o o l i n g data for p r i m a r y phase and eutectic i n t e r f a c e s . The a u t h o r s ' a i m is to p r o v i d e data for a n o m a l o u s s y s t e m s but f i r s t of a l l to p r e s e n t m e a s u r e m e n t s made in n o r m a l s y s t e m s in o r d e r to a s s e s s the f a c t o r s that influence growth t e m p e r a t u r e m e a s u r e m e n t s and to a c c o u n t for the d i s c r e p a n c i e s in p r e v i o u s r e s u l t s . P r e v i o u s m e a s u r e m e n t s in n o r m a l alloys have e s t a b l i s h e d that the r e l a t i o n s h i p b e t w e e n e u t e c t i c i n t e r f a c e u n d e r c o o l i n g and growth v e l o c i t y is of the f o r m , AT
= K v 1/2
[1]
but t h e r e e x i s t s d i s a g r e e m e n t o v e r the magnitude of K and this can be of c o n s e q u e n c e when defining coupled zone b o u n d a r i e s . V a l u e s of 2.3, 2 33.13, 3 and 10.7~ c m -1/e s 1/e (Ref. 4) have b e e n r e p o r t e d for the A1-CuAle s y s t e m . T h e s e s t u d i e s w e r e made d u r i n g h o r i z o n t a l s o l i d i f i c a t i o ne and d u r i n g v e r t i c a l s o l i d i f i c a t i o n 3,~ in o r d e r to e l i m i n a t e effects due to convective m i x i n g in the liquid that may o c c u r d u r i n g h o r i z o n t a l s o l i d i f i c a tion. It is i n t e r e s t i n g to note that J o r d a n and Hunt s have d e m o n s t r a t e d that i d e n t i c a l r e s u l t s can be obt a i n e d f r o m h o r i z o n t a l and v e r t i c a l s o l i d i f i c a t i o n s t u d i e s . In o r d e r that the p r e s e n t u n d e r c o o l i n g m e a s u r e m e n t s could be c o m p a r e d with p r e v i o u s s t u d i e s , i n t e r f a c e growth t e m p e r a t u r e s were m e a s u r e d in the A1-CuA12 s y s t e m d u r i n g h o r i z o n t a l growth u s i n g an app a r a t u s s i m i l a r to that d e s c r i b e d b y Moore and E l l i o t t 6 but i n c o r p o r a t i n g the t h e r m o c o u p l e a r r a n g e m e n t used by J o r d a n and HuntP T h i s change was made in o r d e r to e l i m i n a t e a l a r g e l y i n d e t e r m i n a b l e e r r o r that may a r i s e f r o m heat flow along t h e r m o c o u p l e w i r e s if they do not lie in a n i s o t h e r m a l p l a n e . T h e s e m e a s u r e m e n t s were extended to the S n - C d s y s t e m followed by m e a s u r e m e n t s in the s a m e s y s t e m d u r i n g v e r t i c a l s o l i d i fication u s i n g an a p p a r a t u s s i m i l a r to that d e s c r i b e d
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