The structure of a partially solid alloy
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a n u m b e r of p a p e r s p u b l is h e d in the p a s t few y e a r s the p r a c t i c a l a p p l i c a t i o n s of a new m e t a l f o r m ing p r o c e s s , R h e o c a s t i n g , w e r e d e s c r i b e d . 1-3 F u n d a m e n t a l a s p e c t s of the p r o c e s s r e l a t i n g s t r u c t u r e of a p a r t i a l l y s o l i d i f i e d , v i g o r o u s l y a g i t a t e d , Sn-15 pct Pb a l l o y to its t h e o l o g i c a l b e h a v i o r w e r e s t u d ie d in a high t e m p e r a t u r e v i s c o m e t e r . 4 The work described herein is a continuation of this l a t t e r study c a r r i e d out on a continuous s l u r r y p r o d u c t i o n a p p a r a t u s . T h i s a p p a r a tus was s p e c i f i c a l l y d e s i g n e d to p e r m i t c l o s e c o n t r o l of p r o c e s s v a r i a b l e s d u r i n g p a r t i a l s o l i d i f i c a t i o n . General relationships are developed between process v a r i a b l e s d u r i n g s l u r r y p r o d u c t i o n and the s t r u c t u r e of the p r i m a r y s o l i d p a r t i c l e s . E a r l i e r w o r k c a r r i e d out on a high t e m p e r a t u r e v i s c o m e t e r 4 has shown that the s t r u c t u r e and r h e o l o g i c a l b e h a v i o r of a Sn-15 pct Pb a ll o y s l u r r y a r e a function p r o c e s s v a r i a b l e s . The general trends established r e lating p r o c e s s v a r i a b l e s to the s t r u c t u r e and the v i s c o s i t y of the m e t a l s l u r r i e s w e r e : a) I n c r e a s i n g the a v e r a g e s h e a r r a t e g e n e r a l l y r e d u c e s the a m o u n t of e n t r a p p e d liquid in the s o l i d p a r t i c l e s r e s u l t i n g in a c o r r e s p o n d i n g d e c r e a s e in v i s c o s i t y . S h e a r r a t e a l s o a f f e c t s the s i z e of the p r i m a r y p a r t i c l e s at s l o w c o o l ing r a t e s - p r i m a r y s o l i d p a r t i c l e s i z e d e c r e a s e s with i n c r e a s i n g a v e r a g e s h e a r r a t e . b) I n c r e a s i n g the a v e r a ge co o l i n g r a t e d u r i n g p r i m a r y s o l i d i f i c a t i o n r e d u c e s the s i z e of the p r i m a r y s o l i d p a r t i c l e s , but i n c r e a s e s the amount of e n t r a p p e d l i q u i d - i n c r e a s e s the e f f e c t i v e v o l u m e f r a c t i o n of s o l i d in the s l u r r y , h e n c e i n c r e a s e s its v i s c o s i t y , c) A s the v o l u m e f r a c t i o n s o l i d in a s l u r r y i n c r e a s e s so d o e s its v i s c o s i t y , d) F o r a g i v e n a v e r a g e s h e a r and c o o l i n g r a t e , the r e l a t i v e v i s c o s i t y *
of a p a r t i a l l y s o l i d m e t a l s l u r r y , ~r, at v o l u m e f r a c t i o n s s o l i d l a r g e r than ~ 0 .2 , can be d e s c r i b e d by an e x p o n e n t i a l eq u at i o n ,
[i]
r/r = A exp B g s
w h e r e A and B a r e c o n s t a n t s d e p e n d i n g on a v e r a g e s h e a r and c o o l i n g r a t e s , and gs is v o l u m e f r a c t i o n s o l i d ,
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