Abnormal grain growth in TD-nickel
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PETROVIC
AND
L.J.
EBERT
C h a r a c t e r i s t i c s of t h e c o a r s e g r a i n t r a n s f o r m a t i o n o c c u r r i n g in T D - n i c k e l 1 in. b a r u n d e r c e r t a i n c o n d i t i o n s of d e f o r m a t i o n and a n n e a l i n g w e r e e x a m i n e d . The t r a n s f o r m a t i o n e x h i b i t s A v r a m i - t y p e k i n e t i c s , with an a c t i v a t i o n e n e r g y of 250 k c a l p e r m o l e . C h a r a c t e r i s t i c s of u n t r a n s f o r m e d r e g i o n s a r e l i k e t h o s e of the a s - r e c e i v e d s t a t e . The t r a n s f o r m e d g r a i n s i z e i n c r e a s e s with i n c r e a s i n g d e f o r m a t i o n and d e c r e a s i n g a n n e a l i n g t e m p e r a t u r e . T r a n s f o r m e d g r a i n s have a {7, 5, 15}(5, 14, 7} a n n e a l i n g t e x t u r e . The c o a r s e g r a i n t r a n s f o r m a t i o n i s s i g n i f i c a n t l y d i f f e r e n t f r o m p r i m a r y r e c r y s t a l l i z a t i o n in p u r e n i c k e l . Its c h a r a c t e r i s t i c s cannot be r a t i o n a l i z e d in t e r m s of p r i m a r y r e c r y s t a l l i z a t i o n c o n c e p t s , but m a y b e e x p l a i n e d in t e r m s of an a b n o r m a l g r a i n g r o w t h d e s c r i p t i o n . T h i s p r o v i d e s s u p p o r t f o r the s u g g e s t i o n , d e d u c e d f r o m the p r e v i o u s e l e c t r o n m i c r o s c o p y i n v e s t i g a t i o n , that the c o a r s e g r a i n t r a n s f o r m a t i o n in T D - n i c k e l i s a b n o r m a l g r a i n g r o w t h r a t h e r t h a n p r i m a r y r e c r y s t a l l i z a t i o n . The a n a l y s i s s u g g e s t s an e x p l a n a t i o n f o r the effect of " t h e r m o m e c h a n i c a l h i s t o r y " on the d e f o r m a t i o n and a n n e a l i n g b e h a v i o r of T D - n i c k e l .
AN e l e c t r o n
m i c r o s c o p y study of t h e p r i m a r y r e c r y s t a l l i z a t i o n of T D - n i c k e l by the p r e s e n t a u t h o r s has s u g g e s t e d that, in T D - n i c k e l 1 in. b a r , a b n o r m a l g r a i n g r o w t h , r a t h e r than p r i m a r y r e c r y s t a l l i z a t i o n , i s the p r o c e s s by w h i c h a c o a r s e g r a i n s t r u c t u r e i s p r o d u c e d f r o m the i n i t i a l l y f i n e - g r a i n e d s t a t e a f t e r s u i t a b l e c o n d i t i o n s of d e f o r m a t i o n and annealing.1 To p r o v i d e f u r t h e r s u p p o r t for t h i s contention, c h a r a c t e r i s t i c s of t h i s c o a r s e g r a i n t r a n s f o r m a t i o n w e r e e x a m i n e d . The k i n e t i c s of the p r o c e s s w e r e d e t e r m i n e d . E f f e c t s of d e f o r m a t i o n s e v e r i t y and a n n e a l i n g t e m p e r a t u r e on the t r a n s f o r m e d g r a i n s i z e w e r e e x a m i n e d q u a n t i t a t i v e l y . A p o l e f i g u r e of t r a n s f o r m e d g r a i n o r i e n t a t i o n s w a s o b t a i n e d . D e f o r m a t i o n and a n nealing subs
