Ordering kinetics in Ni 3 Mn
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Ordering Kinetics in Ni Mn c~ JO0
M. KIRK AND J. B. COHEN T h e r e is i n c r e a s e d i n t e r e s t in the o r d e r - d i s o r d e r t r a n s f o r m a t i o n in NisMn, in s t u d i e s of r a d i a t i o n d a m age ~ and in the k i n e t i c s of the t r a n s f o r m a t i o n c l o s e to 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 . 2'3 This alloy has the L1 a s t r u c t u r e s i m i l a r to Cu~Au. 4 Changes in p r o p e r t i e s with o r d e r i n g t i m e have been followed, ~ and t h e r e have been s o m e X - r a y s t u d i e s , 6 but t h e s e did not s e p a r a t e the k i n e t i c s of d o m a i n growth and o r d e r within the dom a i n s . This is the p u r p o s e of this c o m m u n i c a t i o n . To obtain adequate X - r a y i n t e n s i t i e s , s i n g l e c r y s t a l s a r e r e q u i r e d b e c a u s e of the s i m i l a r i t i e s in s c a t t e r i n g f a c t o r s of Ni a n d Mn. These w e r e grown by the B r i d g e m a n technique. A s u i t a b l e c h a r g e of 99.997 pct p u r e Ni and 99.99 pct p u r e Mn was loaded into a t a p e r e d h i g h - p u r i t y a l u m i n a c r u c i b l e with a l o o s e - f i t t i n g top. High p u r i t y argon at about 1.5 t i m e s a t m o s p h e r e p r e s s u r e was i n t r o d u c e d 30 m i n a f t e r m e l t i n g (at a v a c u u m of 10 -6 T o r r ) to r e d u c e m a n g a n e s e l o s s e s , but a 15 to 20 pet i n c r e a s e in the weight of Mn over that for s t o i c h i o m e t r y was s t i l l needed. A v e r t i c a l m o l y b d e n u m - w o u n d f u r n a c e , p r o t e c t e d with h y d r o g e n gas was r a i s e d past the c r u c i b l e at 2 m m p e r h with a g r a d i e n t of 2~ per m m . C r y s t a l s a p p r o x i m a t e l y 0.3 m long and 0.01 m in d i a m w e r e obtained. Slices 2 • 10 -3 m thick w e r e cut to within 2 deg of {100} p l a n e s . The c o m p o s i t i o n was obtained within an u n c e r t a i n t y of • at. pct f r o m m e a s u r e m e n t s of l a t t i c e p a r a m e t e r and published data on this quantity, v The s l i c e e m p l o y e d i n this study had a c o m p o s i t i o n of 26.75 at. pct Mn. The c o m p o s i t i o n a l u n i f o r m i t y a c r o s s the face was checked by a m i c r o f l u o r e s c e n c e t e c h n i q u e ; this v a r i a t i o n was • pct or l e s s . (The v a r i a t i o n along the length of an e n t i r e c r y s t a l was 2 pct or l e s s . ) The s l i c e was polished m e t a l l o g r a p h i c a l l y , etched in a b o i l i n g s o l u t i o n of one p a r t a c e t i c acid, one p a r t n i t r i c acid, and four p a r t s d i s t i l l e d w a t e r , and quenched f r o m 512~ All r e s u l t s of X - r a y d i f f r a c t i o n r e p o r t e d h e r e w e r e obtained with a G. E. d i f f r a c t o m e t e r and a s c i n t i l l a t i o n d e t e c t o r with a p u l s e - h e i g h t a n a l y z e r s e t for 90 pct a c c e p t a n c e of f i l t e r e d F e K a r a d i
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