The growth of antiphase domains in Cu 3 Au as studied by transmission electron microscopy
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The changes i n the a n t i p h a s e d o m a i n s t r u c t u r e of s t o i c h i o m e t r i c Cu3Au d u r i n g o r d e r i n g after quenching f r o m above T c have been s t u d i e d by m e a n s of 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 . The growth of the d o m a i n s was found to s a t i s f y a D a ~ t r e l a t i o n in a g r e e m e n t with p r e v i o u s X - r a y diffraction m e a s u r e m e n t s . The a c t i v a t i o n energy d e t e r m i n e d for the p r o c e s s (42 kcal per mole) is a l s o i n a g r e e m e n t with the p r e v i o u s work. An i n c r e a s e in q u e n c h i n g t e m p e r a t u r e gave no effect on the d o m a i n s i z e achieved by a p a r t i c u l a r o r d e r i n g t r e a t m e n t . M e a s u r e m e n t s of the dom a i n s i z e d i s t r i b u t i o n at v a r i o u s s t a g e s d u r i n g growth i n d i c a t e that the d o m a i n s t r u c t u r e is not c o m p l e t e l y i r r e g u l a r . C e r t a i n d o m a i n s i z e s which a r e m u l t i p l e s of a unit d o m a i n s i z e a r e p r e f e r r e d . D u r i n g the e a r l y stages of d o m a i n growth the behavior a p p e a r s to be c o n s i s t e n t with a diffusion model of the o r d e r i n g p r o c e s s s i m i l a r to that applied to spinodal decomposition. S T O I C H I O M E T R I C Cu~Au tends to form a n o r d e r e d s t r u c t u r e of the L12 type below its c r i t i c a l t e m p e r a t u r e T c ~ 390~ The " d i s o r d e r e d " state of the alloy, which is an fcc a t o m a r r a n g e m e n t having only s h o r t r a n g e o r d e r , c a n be p r e s e r v e d by quenching f r o m above T c to r o o m t e m p e r a t u r e . Subsequent a n n e a l i n g of the quenched alloy below T c allows o r d e r i n g to occur through the f o r m a t i o n and growth of o r d e r e d r e ~ o n s called a n t i p h a s e d o m a i n s . It is g e n e r a l l y thought that these a n t i p h a s e d o m a i n s i n s t o i c h i o m e t r i c Cu3Au a r e n e v e r i n t h e r m a l e q u i l i b r i u m , but a r e t r a n s i e n t ones a p p e a r i n g d u r i n g the o r d e r i n g p r o c e s s and d i s a p p e a r i n g in the fully o r d e r e d s t a t e . Also, although an a n t i p h a s e d o m a i n s t r u c t u r e f o r m s on o r d e r i n g i n Cu3Au , it has g e n e r a l l y been s t a t e d that the d o m a i n s have i r r e g u l a r s i z e s . This g e n e r a l behavior is i n c o n t r a s t with the l o n g - p e r i o d s u p e r l a t t i c e s f o r m e d at other c o m p o s i t i o n s i n the s a m e a l l o y s y s t e m such as CuAu II and CuaAu IT. B e c a u s e a r e c e n t X - r a y d i f f r a c t i o n study 1 of the s t o i c h i o m e t r i c alloy has shown that a r e g u l a r i t y in the d o m a i n b o u n d a r y c o n f i g u r a t i o n may exist d u r i n g the initial s t a g e s of the o r d e r i n g p r o c e s s , the a i m of this r e s e a r c h has been to study by m e a n s of t r a n s
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