The kinetics of isothermal and isovelocity pearlite growth in Cu-Al eutectoid alloy
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M e a s u r e m e n t s of p e a r l i t e growth r a t e and i n t e r l a m e l l a r s p a c i n g have b e e n m a d e on i s o t h e r m a l l y t r a n s f o r m e d s p e c i m e n s of C u - l l . 8 wt p c t Al e u t e c t o i d a l l o y . Growth r a t e s which have been c a l c u l a t e d on the a s s u m p t i o n that v o l u m e diffusion in the p a r e n t fl p h a s e is the r a t e c o n t r o l l i n g p r o c e s s show e x c e l l e n t a g r e e m e n t with the m e a s u r e d v a l u e s . D i r e c t i o n a l c o n t r o l of e u t e c t o i d g r o w t h b y t r a n s l a t i n g s p e c i m e n s t h r o u g h s t e e p t e m p e r a t u r e g r a d i e n t s r e s u l t e d in the f o r m a t i o n of a l i g n e d l a m e l l a r s t r u c t u r e s , and the effect of v a r i a t i o n s in i m p o s e d v e l o c i t y and t e m p e r a t u r e g r a d i e n t on a l i g n m e n t h a s b e e n e x a m i n e d . A c o m p a r i s o n of the k i n e t i c s of the two m o d e s of t r a n s f o r m a t i o n h a s shown that i s o t h e r m a l and i s o v e l o c i t y p e a r l i t e growth in t h i s a l l o y m a y be r e a d i l y i n t e r r e l a t e d . A n a l y s i s of the i s o v e l o c i t y g r o w t h d a t a s u p p o r t s the c o n c l u s i o n that growth is c o n t r o l l e d b y v o l u m e diffusion.
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u s u a l m e t h o d of e x a m i n i n g the r a t e c o n t r o l l i n g p r o c e s s f o r the growth of p e a r l i t e is to m e a s u r e the p a r a m e t e r s of growth r a t e and i n t e r l a m e l l a r s p a c i n g a s a function of t e m p e r a t u r e , u s i n g i s o t h e r m a l l y t r a n s f o r m e d s p e c i m e n s , and to a n a l y z e t h i s d a t a in the light of the t h e o r i e s f o r p e a r l i t e growth. An a l t e r n a t i v e t r a n s f o r m a t i o n t e c h n i q u e is to s l o w l y t r a n s l a t e a s p e c i m e n of the e u t e c t o i d a l l o y t h r o u g h a s t e e p t e m p e r a t u r e g r a d i e n t at a c o n s t a n t v e l o c i t y . l - a This p r o c e d u r e is s i m i l a r to that u s e d in the p r o d u c tion of a l i g n e d l a m e l l a r s t r u c t u r e s in e u t e c t i c a l l o y s , and under the c o r r e c t c o n d i t i o n s , can l e a d to a l i g n m e n t in e u t e c t o i d a l l o y s . In d i r e c t i o n a l , o r i s o v e l o c i t y t r a n s f o r m a t i o n , the g r o w t h r a t e of the p e a r l i t e is f i x e d b y the i m p o s e d t r a n s l a t i o n v e l o c i t y and the t r a n s f o r m a t i o n t e m p e r a t u r e is a f r e e v a r i a b l e , w h e r e a s in i s o t h e r m a l t r a n s f o r m a t i o n the t r a n s f o r m a t i o n t e m p e r a t u r e is f i x e d and the growth r a t e i s a l l o w e d to v a r y . I s o v e l o c i t y t r a n s f o r m a t i o n t e c h n i q u e s not only p r o v i d e a m e t h o d of p r o d u c i n g an a l i g n e d c o m p o s i t e m a t e r i a l grown in situ, but
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