A transparent model for simulation of ingot front solidification
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a t u r e a n d l i q u i d s u p e r h e a t in our p a r t i c u l a r c o n f i g u r a t i o n . F o r l o w s u p e r h e a t t h e r e is i s o t r o p y o n l y w h e n t h e m o l d t e m p e r a t u r e is n e a r t h e f r e e z i n g t e m p e r a t u r e . A t h i g h e r v a l u e s of t h e s u p e r h e a t , t h e i n t e r f a c e f r e e z e s i s o t r o p i c a l l y no m a t t e r w h a t t h e m o l d t e m p e r a t u r e s . A t y p i c a l a n i s o t r o p i c i n t e r f a c e r e v e a l e d by d e c a n t i n g is shown in Fig. 1. In o r d e r t o e x a m i n e t h i s b e h a v i o r m o r e f u l l y , t h e c o n d i t i o n s at t h e solid-!iquid i n t e r f a c e were v a r i e d w h i l e identical conditiofis were maintained at t h e m o l d i n g o t i n t e r f a c e . A n i n g o t o f w a t e r w a s c a s t f r o m 5°C s u p e r h e a t into a n a l u m i n u m m o l d a t - 1 9 6 ° C . T h r e e min l a t e r , and a f t e r a 5 - m m thick anisotropic s h e l l h a d f o r m e d , see T a b l e I, t h e unsolidified l i q u i d w a s d e c a n t e d . W a t e r a t 80°C s u p e r h e a t w a s t h e n p o u r e d i n t o t h i s c a v i t y a n d f r e e z i n g was a l l o w e d t o c o n t i n u e ; F i g . 2 s h o w s t h a t t h e r e h a s b e e n no c h a n g e i n the i n t e r face shape, and the anisotropy r e m a i n s . In the conv e r s e e x p e r i m e n t , w a t e r s u p e r h e a t e d t o 80°C w a s c a s t into a m o l d h e l d a t - 1 9 6 ° C so t h a t a n i s o t r o p i c interface f o r m e d . Following decanting, and a f t e r
Fig. 1--Typical anisotropic g r o w t h b e h a v i o r in an ingot of p u r e w a t e r c a s t from 20°C s u p e r h e a t into a mold held at -196°C. A c o l o r e d die was added midway during g r o w t h w h i c h was t e r minated by decanting 4 min a f t e r c a s t i n g .
Table 1. The Effect o f Superheat and Mold Temperature on Interface Anisotropy
Interface-Anisotropy Mold Temperature, °C
Superheat
Yes
No
-196 -80 -30 -10
5 5 5 S
-196 -70 -10
20 20 20
X
-196 -70
80 80
X X
R E S U L T S A N D DISCUSSION i) P u r e W a t e r : M o l d T e m p e r a t u r e and Superheat Variations T a b l e I l i s t s t h e o b s e r v a t i o n s r e l e v a n t to t h e dev e l o p m e n t of a n i s o t r o p y a s a f u n c t i o n o f m o l d t e m p e r J. C1SSF., G. S. COLE, and G. F. BOLLING are with the Scientific Research Staff, Process Research Department, Ford Motor Co., Dearborn, Mich. Manuscript submitted April 8 , 1971. METALLURGICAL TRANSACTIONS
VOLUME 2 , NOVEMBER 1971-3243
Fig. 2--An ingot of ice h a s been s o l i d i f i e d anisotropically. A f t e r decanting the unsolidified l i q u i d , hot w a t e r (80°C) w a s a d d e d t o the cavity. Some r e m e l t i n g h a s o c c u r r e d w h i c h a c c o u n t s f o r the lack of anisotropy at the left portion of the ingot, but in g e n e r a l , most of the anisotropy continues with the freezing.
Fig. 4--An example of c r a c k s only dev
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