On a new intermetallic phase in the nickel-tungsten system
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On a New Intermetallic Phase in the Nickel-Tungsten System
new phase a r e given in Table I. The data w e r e indexed b y I t o ' s method 4 as o r t h o r h o m b i c with a o = 7.76/~, b o = 12.48.~, and c o = 7.10/~. All 42 l i n e s o b s e r v e d could be accounted for by this s t r u c t u r e ; t h e r e w e r e no u n identified l i n e s . This new i n t e r m e t a l l i c p h a s e which we call 6 fits the f o r m u l a NiW with a v e r y n a r r o w hom o g e n e i t y r a n g e as d e t e r m i n e d by e l e c t r o n m i c r o p r o b e a n a l y s i s . The p o s s i b i l i t y of an i m p u r i t y s t a b i l i z e d phase does not s e e m l i k e l y b e c a u s e high p u r i t y s t a r t ing m a t e r i a l s and i n e r t a t m o s p h e r e s w e r e used. F u r t h e r m o r e , in addition to t u n g s t e n m e a s u r e m e n t s , n i c k e l m e a s u r e m e n t s w e r e made on the i n t e r m e t a l l i c and the c o m b i n e d nickel and t u n g s t e n c o n t e n t s in all c a s e s were equal to 100 wt pct well within an e r r o r of 2 wt pct. This r e s u l t s u g g e s t s that the p r e s e n c e of a c a r bide, b e t i d e or other s i m i l a r compound is unlikely. I n t e r m e d i a t e p h a s e s have often b e e n r e p o r t e d at or n e a r the e q u i a t o m i c c o m p o s i t i o n in s y s t e m s of the t r a n sition m e t a l s Fe, Co, and Ni (B p a r t n e r s ) with Group IV, V, and VI e l e m e n t s of the second and t h i r d long p e r i o d s (A p a r t n e r s ) . 5'8'7 In p a r t i c u l a r , t u n g s t e n is the only A e l e m e n t that has not p r e v i o u s l y b e e n shown to f o r m a n e a r e q u t a t o m i c i n t e r m e t a l l i c with n i c k e l . Since an o r t h o r h o m b i c 5NiMo phase is found c l o s e to the e q u i a t o m i c c o m p o s i t i o n in the n i c k e l - m o l y b d e n u m s y s t e m 8
J. M. WALSH AND M. J. DONACHIE, JR. Table I. X-Ray Diffraction Data for NiW Intermetallic Phase
DURINGan t n t e r d l f f u s i o n study in the n i c k e l - t u n g s t e n
hkl
dObserved
dCalculated
s y s t e m 1'2 s e v e r a l diffusion couples were e x a m i n e d that c o n t a i n e d a p r e v i o u s l y u n r e p o r t e d i n t e r m e t a l l i c phase. This phase was p r e s e n t in couples a n n e a l e d 100 h at 1000~ and 112 h at 1038~ but was not o b s e r v e d in couples a n n e a l e d 60 h at 1093~ or in couples a n n e a l e d at t e m p e r a t u r e s up to 1316~ An additional a n n e a l of 488h at 1038~ r e s u l t e d in a slight thickening of the i n t e r m e t a l l i c phase l a y e r . Starting m a t e r i a l for the diffusion couples was J o h n s o n - M a t t h e y s p e c t r o g r a p h i c n i c k e l and t u n g s t e n rod. The a n n e a l s were c a r r i e d out in h e l i u m filled q u a r t z a m p o u l e s as d e s c r i b e d In Refs. 1 and 2. The new phase was o b s e r v e d on the t u n g s t e n side of the solid solution diffusion zone (Fig. 1). Repe
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