Macrosegregation in a copper alloy directionally cast with exudation of liquid
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TI N V E R S E s e g r e g a t i o n a n d e x u d a t i o n s a r e o f t e n o b s e r v e d in chill c a s t i n g s , i n c l u d i n g c o n t i n u o u s c a s t i n g . T h e i n v e r s e s e g r e g a t i o n is p r i m a r i l y a s s o c i a t e d w i t h the r e g i o n o f t h e c a s t i n g n e a r t h e c h i l l f a c e a n d i s a t t r i b u t e d t o b a c k f l o w of l i q u i d e n r i c h e d i n s o l u t e . 1-4 The b a c k f l o w o c c u r s as a r e s u l t o f v o l u m e s h r i n k a g e , this shrinkage resulting f r o m solidification a n d dec r e a s i n g specific l i q u i d volume with temperature. The i n c r e a s e in s o l u t e c o n c e n t r a t i o n r e s u l t i n g f r o m i n v e r s e s e g r e g a t i o n is a m a x i m u m at t h e c h i l l f a c e a n d i s r e l a t i v e l y s m a l l . In the A 1 - C u s y s t e m t h e m a x i m u m i n c r e a s e is 0.5 p c t f o r t h e A I - 1 0 p c t Cu a l l o y . 2 E x u d a t i o n s a r e o b s e r v e d on the c h i l l f a c e , a n d in contrast t o i n v e r s e segregation c a n h a v e v e r y high solute concentrations, s T h e y are b e l i e v e d t o r e s u l t f r o m s e p a r a t i o n of t h e c a s t i n g f r o m the c h i l l s u r f a c e , c a u s i n g l o c a l r e h e a t i n g a n d p a r t i a l r e m e l t i n g of t h e s o l i d casting. L i q u i d f l o w s through r e m e l t e d channels, p a s t t h e o r i g i n a l cast f a c e to f o r m t h e e x u d a t i o n s . Both i n v e r s e segregation and exudations o c c u r u n d e r s i m i l a r c o n d i t i o n s a n d i n t h e s a m e r e g i o n s of t h e c a s t ing. A c c o r d i n g l y it a p p e a r e d d e s i r a b l e to m e a s u r e t h e macrosegregation a s s o c i a t e d w i t h b o t h of t h e s e e f f e c t s q u a n t i t a t i v e l y i n a g i v e n a l l o y . In p a r t i c u l a r , we w i s h e d to k n o w in what w a y t h e e x u d a t i o n p r o c e s s a f f e c t e d t h e s o l u t e d i s t r i b u t i o n w i t h i n the c a s t i n g n e a r the c h i l l f a c e , s i n c e t h i s is w h e r e t h e i n v e r s e s e g r e g a t i o n is m e a s u r e d . A d a m s a n d F r i c k e ,4'6 i n d i r e c t i o n a l l y c a s t A 1 - C u a l l o y o b s e r v e d a s o l u t e - d e p l e t e d z o n e a b o u t 0.1 in. f r o m the c h i l l f a c e . A d a m s4 n o t i c e d a t h i n e x u d e d l a y e r a t t h e c h i l l f a c e , but m a d e n o c o r r e l a t i o n b e t w e e n the p r e s e n c e of e x u d a t i o n s a n d the d e p l e t e d z o n e . F r i c k e6 on the o t h e r h a n d o b s e r v e d s m a l l p r o t u b e r a n c e s on the c h i l l f a c e w h i c h h e a s s o c i a t e d w i t h i n t e r d e n d r i t i c v o i d s w i t h i n the c a s t i n g s . T h e s e v o i d s w o u l d in e f f e c t r e d u c e t h e a v e r a g e s o l u t e c o n c e n t r a t i o n i n the casting, producing a depleted zone. S i n c e both segregation effects o c c u r
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