Interdendritic fluid flow and macrosegregation; influence of gravity
- PDF / 1,928,628 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 61 Downloads / 259 Views
IN a
s e r i e s of r e c e n t p a p e r s we have e x a m i n e d a n a l y t i c a l l y and e x p e r i m e n t a l l y m a c r o s e ~ r e g a t i o n which r e s u l t s from i n t e r d e n d r i t i c fluid flow. -4 In that work, d e t a i l s of fluid flow b e h a v i o r were a s s u m e d (without h y d r o d y n a m i c c a l c u l a t i o n ) , and r e s u l t i n g m a c r o s e g r e gation behavior was then calculated. The sole d r i v i n g force for the a s s u m e d flow was l i q u i d - s o l i d s h r i n k a g e , and e x p e r i m e n t s were such that this was the only d r i v ing force operating. Solute a n d / o r t h e r m a l l y induced convection were not p r e s e n t in e x p e r i m e n t s p e r f o r m e d s i n c e solidification was u n i d i r e c t i o n a l upwards, with liquid density d e c r e a s i n g in the v e r t i c a l d i r e c t i o n . In this paper we now c o n s i d e r the h y d r o d y n a m i c s of i n t e r d e n d r i t i c fluid flow, a s influenced by s o l i d i f i c a t i o n c o n t r a c t i o n , liquid c o n t r a c t i o n d u r i n g s o l i d i f i c a t i o n , a n d g r a v i t y a c t i n g on a fluid of v a r i a b l e d e n s i t y . We view the l i q u i d - s o l i d r e g i o n of a c a s t i n g or ingot a s a porous m e d i u m in which v o l u m e f r a c t i o n of p o r o s i t y v a r i e s with f r a c t i o n solid and is c o n t i n u o u s l y changing d u r i n g solidification. The size of individual p o r e s depends both on f r a c t i o n solid and m i c r o s t r u c t u r e ( e . g . , d e n d r i t e a r m spacing). Standard t e c h n i q u e s for c a l c u l a t ing flow through porous m e d i a a r e applied to this s p e c i a l i z e d p r o b l e m , and final m a c r o s e g r e g a t i o n det e r m i n e d from the c a l c u l a t e d flow d i s t r i b u t i o n . Solut i o n s a r e l i m i t e d in this paper to the t i m e - i n d e p e n d e n t case of h o r i z o n t a l , u n i d i r e c t i o n a l , s t e a d y - s t a t e s o l i d i fication; c o m p a r i s o n of theory with e x p e r i m e n t will be c o n s i d e r e d in a l a t e r p a p e r . It will be seen that the n a t u r e and extent of the s e g r e g a t i o n a r e s t r o n g l y i n f l u e n c e d , for e x a m p l e s cited h e r e i n , by changes in liquid d e n s i t y d u r i n g s o l i d i f i c a tion. They a r e also i n f l u e n c e d by solidification r a t e and t e m p e r a t u r e g r a d i e n t , phase d i a g r a m c h a r a c t e r i s t i c s , and r e s i s t a n c e of the l i q u i d - s o l i d r e g i o n to i n t e r d e n d r i t i c flow. Conditions n e c e s s a r y for f o r m a t i o n of " c h a n n e l t y p e " s e g r e g a t e s will be q u a n t i t a t i v e l y d e s c r i b e d . T h e s e s e g r e g a t e s ( e . g . , " f r e c k l e s " ) have
p r e v i o u s l y b e e n shown in two i m p o r t a n t p a p e r s s'6 to r e s u l t f r o m i n t e r d e n d r i t i c fluid flow. S
Data Loading...
