Dendritic peculiarities in undercooled and internally chilled Fe-25 Pct Ni alloy
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Dendritic Peculiarities in Undercooled and Internally Chilled Fe-25 Pct Ni Alloy T. Z. KATTAMIS T H E m o r p h o l o g i c a l m o d i f i c a t i o n s of the bulk u n d e r c o o l e d d e n d r i t i c s t r u c t u r e in F e - 2 5 pct Ni alloy which o c c u r with i n c r e a s i n g d e g r e e of u n d e r c o o l i n g have been p r e v i o u s l y studied. 1'2 It was shown t h e r e i n that for a d e g r e e of u n d e r c o o l i n g l o w e r than 170~ d e n d r i t e s cons i s t of c y l i n d r i c a l a r m s o r t h o g o n a l l y a r r a n g e d in a n o n f e r n - l i k e p a t t e r n and that for a d e g r e e of u n d e r c o o l ing h i g h e r than 170~ d e n d r i t e s d e g e n e r a t e into s p h e r e s . It was also shown 2 that n i c k e l c o n c e n t r a t i o n is lowest at the c e n t e r of the d e n d r i t e a r m o r s p h e r e and i n c r e a s e s g r a d u a l l y with d i s t a n c e f r o m this c e n t e r r e a c h i n g a m a x i m u m at s o m e i n t e r d e n d r i t i c o r i n t e r s p h e r i c a l location. In u n d e r c o o l e d and i n t e r n a l l y c h i l l e d ingots the bulk dendritic m o r p h o l o g y was not modified by the chilling. H o w e v e r , the d i s t r i b u t i o n of n i c k e l was b a s i c a l l y changed, and d e n d r i t e a r m s o r s p h e r e s had exhibited high solute c o r e s . 3 A c l o s e e x a m i n a t i o n of the m a c r o s t r u c t u r e of u n d e r c o o l e d and i n t e r n a l l y c h i l l e d ingots r e v e a l s the e x i s t T. Z. KATTAMIS is Associate Professor, Department of Metallurgy, Institute of Materials Science, The University of Connecticut, Storrs, Conn. Manuscript submitted December 17, 1970. 2 0 0 0 - V O L U M E 2, JULY 1971
of m e a s u r i n g VM q u a n t i t a t i v e l y , h o w e v e r , a c c u r a c y of the method and a p p l i c a t i o n to o t h e r alloy s y s t e m s must be c o n s i d e r e d . S c a t t e r o b s e r v e d in Fig. 2 is m o r e likely r e l a t e d to e r r o r s in q u a n t i t a t i v e m e t a l l o g r a p h y o r to e r r o r s c a u s e d by c o m p a r i n g surface" and bulk m e a s u r e m e n t s r a t h e r than to e r r o r s in H c m e a s u r e m e n t o r d i f f e r e n c e s in alloy c o m p o s i t i o n ; H c for a n n e a l e d a l l o y s v a r
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