Control of ordered structure and ductility of (Fe, Co, Ni) 3 V alloys
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t~.7 DISORDERED (os-quenched)~ 9 CUBIC ORDERED ~' 9 HEXAGONAL ORDERED K 0
of the e/a c o r r e l a t i o n . We b e l i e v e that the e/a is p a r t i c u l a r l y v a l i d in t h e s e o r d e r e d a l l o y s of t r a n s i t i o n e l e m e n t s , in which the s i z e d i f f e r e n c e s a r e s m a l l and the s t a b i l i t y of v a r i o u s o r d e r e d s t r u c t u r e s is bound to be a f f e c t e d to a g r e a t extent by c h a n g e s in the e l e c t r o n s t r u c t u r e . In the study of q u a s i b i n a r y s y s t e m s c o n t a i n ing V and T i t r a n s i t i o n e l e m e n t s , Sinha ~6 o b s e r v e d an a p p r o x i m a t e l y l i n e a r r e l a t i o n of the d e g r e e of h e x a g o n a l i t y of the s t a c k i n g c h a r a c t e r with e/a. On the b a s i s of t h o s e r e s u l t s we a s s e r t that the o r d e r e d s t r u c t u r e in the ( F e , C o , N i h V a l l o y s y s t e m is c o n t r o l l e d by e/a and that the cubic o r d e r e d ~ ' is s t a b l e with e/a - 30 pct F e . H o w e v e r , Sinha and we u s e d d i f f e r e n t t e m p e r a t u r e s to p r o d u c e the o r d e r e d s t r u c t u r e . Since S i n h a ' s s p e c i m e n s w e r e a n n e a l e d at 850~ the o r d e r i n g r e a c tion in the a l l o y s with T c below 850~ cannot be d e t e c t e d f r o m his m e a s u r e m e n t . On the o t h e r hand, our d a t a a p p e a r to a g r e e w e l l with the finding of Van Vucht, 15 who o b s e r v e d the (100) s u p e r l a t t i c e line in the X - r a y d i a g r a m of the V ( C o , F e ) a l l o y containing 12.8 pet Fe. E f f e c t of A t o m i c O r d e r i n g on S t r e n g t h and W o r k H a r d e n i n g B e h a v i o r The influence of a t o m i c o r d e r i n g on the y i e l d s t r e n g t h (cry) at r o o m t e m p e r a t u r e can be r e v e a l e d f r o m c o n s i d e r i n g the l a t t i c e f r a c t i o n a l s t r e s s a g a i n s t METALLURGICAL TRANSACTIONS A
the m o t i o n OI alSlOCatlOIl~ l_rlvD.rluu~ UrU~s ~u ~t~L~o. If atomic ordering does not cause a significant change in frictional stress, the cry m a y not be affected by formation of long range order. This is apparently the
c a s e for the cubic o r d e r e d a l l o y s D and E, w h e r e ay i s about the s a m e in both fully d i s o r d e r e d and o r d e r e d s t a t e s ( F i g . 9). The cry of a l l o y s A, B, and C is h i g h e r in the a s - q u e n c h e d s t a t e than in the fully o r d e r e d s t a t e (Fig. 9). T h e h i g h e r ay in the a s - q u e n c h e d s t a t e is m o s t p r o b a b l y due to the f o r m a t i o n of s t r o n g s h o r t r a n g e o r d e r in t h e s e a l l o y s with hi~her T o , a s i n d i c a t e d by transmission electron mieroscop H o w e v e r , in m a n y c a s e s , the f o r m a t i o n of long r a n g e o r d e r is a c c o m p a n i e d with change in l a t t i c e f r i c t i o n a l s t r e s s t h r o u g h m o d e s , s u c h a s changing the v i b r a t i o n a l
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