Macrosegregation during growth of a dendrite array into a stirred melt at near steady-state conditions
- PDF / 2,458,195 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 179 Views
VERHOEVEN
S o l i d i f i c a t i o n e x p e r i m e n t s on tin a l l o y s h a v e b e e n c a r r i e d o u t w h e r e t h e i n t e r f a c e m o r p h o l o g y c o n s i s t e d of a n a r r a y of d e n d r i t e s a d v a n c i n g a t n e a r s t e a d y - s t a t e c o n d i t i o n s . It w a s f o u n d that a f a i r l y s e v e r e d e g r e e of m i x i n g c h a n g e d t h e d e n d r i t e m o r p h o l o g y a t l o w t e m p e r a t u r e g r a d i e n t s but not a t h i g h e r g r a d i e n t s . In b o t h c a s e s t h e m i x i n g w a s r e l a t i v e l y i n e f f e c t i v e a t p r o d u c i n g a m a c r o s e g r e g a t i o n in t h e p r e s e n c e of t h e d e n d r i t e a r r a y . T h e r e s u l t s m a y be i n t e r p r e t e d a s e v i d e n c e that i n s o m e c a s e s o n e w o u l d e x p e c t v e r y l i t t l e m a c r o s e g r e g a t i o n in c o l u m n a r g r o w t h u n d e r n e a r s t e a d y - s t a t e c o n d i t i o n s e v e n in t h e p r e s e n c e o f s e v e r e liquid convection. W H E N a n alloy solidifies within a n ingot o r casting, the i n t e r f a c e m o r p h o l o g y b e t w e e n t h e s o l i d a n d l i q u i d is p r a c t i c a l l y a l w a y s dendritic. O f t h e l a r g e n u m b e r of c o n t r o l l e d s o l i d i f i c a t i o n e x p e r i m e n t s c a r r i e d o u t i n r e c e n t y e a r s v e r y f e w h a v e b e e n d e v o t e d t o a s t u d y of solidification with an interface morphology consisting of a d e n d r i t e a r r a y . In t h e p r e s e n t w o r k a n a t t e m p t was made t o d e v e l o p e x p e r i m e n t a l t e c h n i q u e s f o r studying the growth of a dendrite a r r a y u n d e r cont r o l l e d c o n d i t i o n s of i n t e r f a c e m o t i o n , h e a t f l o w , a n d f l u i d flow. T h i s i n i t i a l w o r k is c o n c e r n e d w i t h m a c r o segregation d u r i n g dendritic growth. S t u d i e s of m a c r o s e g r e g a t i o n d u r i n g d e n d r i t i c g r o w t h have been mainly concerned with the phenomenon of i n v e r s e s e g r e g a t i o n . T h e o r e t i c a l s t u d i e s 1'2 h a v e s h o w n that a m a c r o s e g r e g a t i o n s h o u l d o c c u r w h e n t h e d e n d r i t e a r r a y i s u n d e r g o i n g a c h a n g e i n l e n g t h a n d that i f the a r r a y m o v e s w i t h a s t e a d y - s t a t e c o n f i g u r a t i o n , m a c r o s e g e r g a t i o n s h o u l d not o c c u r . E x p e r i m e n t a l s t u d i e s1'3 o f d e n d r i t e g r o w t h into r e l a t i v e l y q u i e s c e n t l i q u i d s have given very good agreement with theory. When a d e n d r i t e a r r a y i s m o v i n g u n d e r n e a r s t e a d y s t a t e c o n d i t i o n s o n e h a s a s i t u a t i o n s i m i l a r to " n o r m a l solidification" with a flat solid-liquid i n t e r f a c e . M a c rosegregation for this " n o r m a l solidification" case w i l l be r e f e r r e d t o a s n o r m a l s e g r e g a t i o n .
Data Loading...
