V-Ni system
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The v a n a d i u m - r i c h portion of the V-Ni s y s t e m was i n v e s t i g a t e d by t h e r m a l a n a l y s i s , m i c r o scopic e x a m i n a t i o n , and X - r a y diffraction studies and a phase d i a g r a m i s proposed. The v a n a d i u m solvus was found to exhibit a m a r k e d t e m p e r a t u r e dependence i n c r e a s i n g f r o m 6.8 at. pct Ni at 800~ to 24.0 at. pct Ni at 1280~ A compound having a s u b s t i t u t e d VsNi (A15) type s t r u c t u r e was shown to occur at the s u b s t o i c h i o m e t r i c c o m p o s i t i o n of 22 to 23 at. pct Ni. It f o r m s p e r i t e c t o i d a l l y at 900~ with an enthalpy of f o r m a t i o n of 1595 cal per m o l e . I ~ E C E N T a d v a n c e s in n u c l e a r r e a c t o r technology have brought about an i n t e r e s t in the d e v e l o p m e n t of v a n a d i u m - b a s e alloys a s cladding m a t e r i a l s for fuel e l e m e n t s in the l i q u i d - m e t a l - c o o l e d , fast b r e e d e r r e a c t o r (LMFBR) of the U.S. Atomic E n e r g y C o m m i s s i o n . Vanadium a l l o y s p o s s e s s i n g the d e s i r e d f a b r i c a b i l i t y , high t e m p e r a t u r e s t r e n g t h , and s t a b i l i t y toward n e u t r o n i r r a d i a t i o n have b e e n developed b a s e d p r i m a r i l y on the addition of one or m o r e of the r e f r a c t o r y m e t a l s , T i , C r , Ta, and Nb(Cb). The m a j o r d e t e r r e n t at p r e s e n t is v a n a d i u m ' s s u s c e p t i b i l i t y for oxygen, e i t h e r f r o m the liquid sodium or oxide fuels, with r e s u l t i n g d e g r a d a tion of its m e c h a n i c a l p r o p e r t i e s . Only a l i m i t e d n u m b e r of v a n a d i u m - b a s e a l l o y s have b e e n i n v e s t i g a t e d , however, suggesting a n e e d for phase e q u i l i b r i a i n f o r m a t i o n on additional v a n a d i u m alloy s y s t e m s . Those e l e m e n t s exhibiting e x t e n s i v e or complete solid solub i l i t y in v a n a d i u m a r e of p a r t i c u l a r i n t e r e s t ; and n i c k e l , b e c a u s e of i t s f a v o r a b l e size f a c t o r , would be expected to fall into this c a t e g o r y . A p a r t i a l d i a g r a m h a s b e e n proposed by P e a r s o n and H u m e - R o t h e r y 1 for the V-Ni s y s t e m . They i n v e s t i g a t e d the n i c k e l - r i c h end of the d i a g r a m quite ext e n s i v e l y but r e p o r t e d only v e r y tentative r e s u l t s in the region between 0 and 40 at. pct Ni. R o s t o k e r and Y a m a m o t o 2 r e p o r t e d the o c c u r r e n c e of a new i n t e r m e d i a t e phase which they identified as V3Ni, having a cubic s y m m e t r y of the ~3-W (A15) type, i s o s t r u c t u r a l with V3Co. Its lattice p a r a m e t e r was r e p o r t e d a s 4.70 kX units (4.71/~). L a t e r work by Z e g l e r and Downey 3 c o n f i r m e d the e x i s t e n c e of V3Ni and indicated that it f o r m s by a p e r i t e c t o i d r e a c t i o n s o m e w h e r e b e t w e e n
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