Growth of ternary composites from the melt: Part II
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IN a p r e v i o u s
p a p e r , P a r t I, ~ the c o n d i t i o n s n e c e s s a r y f o r plane f r o n t s o l i d i f i c a t i o n of t e r n a r y a l l o y s with c o m p o s i t i o n s not equal to the e u t e c t i c c o m p o s i t i o n w e r e c a l c u l a t e d . T h i s p a p e r s e t s f o r t h e x p e r i m e n t a l w o r k on the A 1 - C u - N i s y s t e m d e s i g n e d to t e s t the a p p l i c a t i o n of the t h e o r y .
p u r i t y A1 (99.99 p c t ) , Cu (99.9 p c t ) , and Ni (99.9 pct). T e r n a r y a l l o y s of the d e s i r e d c o m p o s i t i o n w e r e then p r e p a r e d f r o m c o m b i n a t i o n s of t h e s e a l l o y s and p u r e a l u m i n u m . S p e c i m e n s w e r e c a s t in the g r a p h i t e c r u c i b l e s using a s p l i t c i r c u l a r g r a p h i t e cup which s e r v e d a s both a funnel and r i s e r for the s p e c i m e n ingot.
A P P A R A T U S AND PROCEDURE The e x p e r i m e n t a l a p p a r a t u s for p r o d u c i n g c r y s t a l s grown u n d e r high t e m p e r a t u r e g r a d i e n t s and with a c o n t r o l l e d growth r a t e was e s s e n t i a l l y the s a m e a s that u s e d by M o l l a r d and F l e m i n g s . 2 The d e s i g n and p r o c e d u r e s w e r e , h o w e v e r , m o d i f i e d to f a c i l i t a t e w o r k ing with the h i g h e r m e l t i n g - p o i n t a l u m i n u m - b a s e alloys. The n e e d s for high t h e r m a l g r a d i e n t and a b s e n c e of c o n v e c t i o n both d i c t a t e a s m a l l s p e c i m e n c r o s s s e c t i o n . The s p e c i m e n g e o m e t r y c h o s e n w a s ~ m . d i a m by 5 in. long r o d s . The c r u c i b l e m a t e r i a l was high p u r i t y g r a p h i t e (99.95 pct) u s e d b e c a u s e of i t s good t h e r m a l conductivity and c h e m i c a l i n e r t n e s s with r e s p e c t to the a l l o y s s t u d i e d . C r u c i b l e s w e r e -ff m . ID, rv m . OD, and 6 in. long. C h r o m e l - a l u m e l t h e r m o c o u p l e s w e r e m a d e f r o m 0.004 in. d i a m w i r e i n s e r t e d in t w i n - b o r e a l u m i n a t h e r m o c o u p l e t u b e s , 0.035 in. OD by 3 in. length. The t h e r m o c o u p l e junction was e x tended about 1 c m beyond the end of the t w i n - b o r e a l u m i n a tube and the w i r e s and junction c o a t e d with liquid p o r c e l a i n c e m e n t . The c r o s s - s e c t i o n of the t h e r m o c o u p l e b e a d p r e p a r e d in this way r e p r e s e n t s l e s s than 5 p c t of the s p e c i m e n c r o s s - s e c t i o n . The t h e r m o c o u p l e s w e r e i n s e r t e d through 0.035 in. d i a m h o l e s d r i l l e d xn" -~' in. d i a m by ~ in. long g r a p h i t e r o d s which s e r v e d to c e n t e r the t h e r m o c o u p l e s in the b o t t o m of the g r a p h i t e c r u c i b l e t u b e s . T h u s e a c h c r u c i b l e c o n t a i n e d a t h e r m o c o u p l e to m e a s u r e the t e m p e r a t u r e g r a d i e n t d u r i n g c
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