Electron microscopy of crystalline and amorphous Ni-P electrodeposited films: In-situ crystallization of an amorphous so
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I, INTRODUCTION W HE d e t a i l e d p r o c e s s by which an a m o r p h o u s m e t a l changes into the e q u i l i b r i u m c r y s t a l l i n e s t a t e is p o o r l y u n d e r s t o o d . On annealing, an a m o r p h o u s m e t a l t r a n s f o r m s into the s t a b l e e q u i l i b r i u m s t a t e by p a s s ing t h r o u g h a s e q u e n c e of p r o g r e s s i v e l y m o r e s t a b l e s t a t e s until the final e q u i l i b r i u m s t a t e is r e a c h e d . 1 Only a few a m o r p h o u s s y s t e m s have b e e n thus f a r inv e s t i g a t e d ; t h e i r t r a n s f o r m a t i o n s a r e c o m p l e x and involve m u l t i p l e m e t a s t a b l e s t a t e s . 2 Not only can a v e r y l a r g e n u m b e r of new a m o r p h o u s m a t e r i a l s be c r e a t e d by r a p i d quenching f r o m e i t h e r the liquid o r v a p o r p h a s e , but m o r e o v e r the c r y s t a l l i z a t i o n of t h e s e a m o r p h o u s m a t e r i a l s s e e m s to spawn one o r m o r e new m e t a s t a b l e c r y s t a l l i n e p h a s e s a s the m a t e r i a l p r o g r e s s e s t o w a r d e q u i l i b r i u m d u r i n g the ann e a l i n g t r e a t m e n t . A v e r y l a r g e n u m b e r of new m e t a s t a b l e c r y s t a l s t r u c t u r e s m a y thus be g e n e r a t e d by a n n e a l i n g an a m o r p h o u s a l l o y of fixed c o m p o s i t i o n . By v a p o r quenching onto s u f f i c i e n t l y cooled s u b s t r a t e s E. VAFAEI-MAKHSOOS is with Department of Chemical Engineering and Materials Science and LOUIS E. TOTH is Professor, Department Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455. EDWIN L. THOMAS is Associate Professor, Department of Polymer Science & Engineering, University of Massachusetts, Amherst, MA 01003. Manuscript submitted April 4, 1977. METALLURGICAL TRANSACTIONS A
p r a c t i c a l l y a l l c h e m i c a l c o m p o s i t i o n s can be d e p o s i t e d in the a m o r p h o u s s t a t e . T h u s the n u m b e r of p o t e n t i a l new m e t a s t a b l e p h a s e s , both a m o r p h o u s and c r y s t a l line, is t r u l y l a r g e . The o v e r a l l t r a n s f o r m a t i o n p r o c e s s can be c a t e g o r i z e d into two s t a g e s : in the f i r s t s t a g e t h e r m a l e n e r g y c a u s e s l o c a l a t o m i c m o v e m e n t s and i n c i p i e n t c r y s t a l l i z a t i o n of m e t a s t a b l e c r y s t a l l i n e s t r u c t u r e s . In the s e c o n d s t a g e t h e r m a l e n e r g y c a u s e s l o n g e r r a n g e a t o m i c m o v e m e n t s and d e c o m p o s i t i o n to the e q u i l i b r i u m p h a s e s a,4 The study of the c r y s t a l l i z a t i o n p r o c e s s e s of a m o r phous a l l o y s has only begun; DSC, X - r a y , e l e c t r i c a l r e s i s t i v i t y and t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y have b e e n p r i m a r y tools f o r s t u d y i n g the t r a n s f o r m a tion p r o c e s
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