Thermodynamics of titanium alloys: III. The Ti-Mo system
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p e a k s , h a v i n g i s o t o p i c a l l y e n r i c h e d t i t a n i u m in o n e side o f t h e t r i p l e K n u d s e n c e l l , a n d t h e a l l o y , o r p u r e 48 t i t a n i u m i n t h e o t h e r . T h e R 46 w a s e v a l u a t e d u s i n g E q . [16] o f U s e l l a n d H o c h ,2 a n d t h e v a l u e s a r e a v e r ages f r o m t h i r t y r e a d i n g s . F r o m t h e s e v a l u e s o f R , t h e titanium a c t i v i t y , a, a n d t h e e x c e s s p a r t i a l free e n e r g y of t i t a n i u m , R T In Z , w a s t h e n p l o t t e d a g a i n s t (1 - - X T i )2 t o g e t F i g s . 1 a n d 2 . T h e e r r o r l i m i t in t h e a c t i v i t y c a l c u l a t i o n s w e r e obt a i n e d by c o m b i n i n g t h e h i g h e s t v a l u e o f R a l l o y w i t h t h e l o w e s t v a l u e of R p u r e so a s t o d e t e r m i n e t h e m a x imum p o s s i b l e e r r o r . T h u s , w h i l e all p o i n t s were p l o t t e d , only t h e m a x i m u m e r r o r i s s h o w n o n t h e f i g u r e s . T h i s p r o c e d u r e s h o w s t h a t t h e e r r o r i n R T In i s r e l a t i v e l y s m a l l ; a r e s u l t due t o t h e r e l a t i v e l y w e a k t i t a n i u m s i g n a l w h i c h m u s t be m e a s u r e d by t h e m a s s spectrometer. S i n c e diffusion in t h e T i - M o s y s t e m is v e r y s l o w , t h e r e i s t h e p o s s i b i l i t y that p a r t o f t h i s e r r o r i s c a u s e d by t i t a n i u m o n t h e s a m p l e s u r f a c e . T h i s w o u l d c a u s e l o w e r activity, and thus a l o w e r activity coeffic i e n t than w o u l d be e x p e c t e d i f no d e p l e t i o n took p l a c e . W h i l e t h i s d e p l e t i o n is m u c h s m a l l e r in a K n u d s e n
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O This research 1900°K • This research 1840°K
MATERIALS T h e i s o t o p i c a l l y e n r i c h e d T i46 w a s f r o m t h e s a m e b a t c h a s w a s u s e d i n t h e w o r k o n t i t a n i u m - a l u m i n u m .2 T h e T i - M o alloys were obtained f r o m Dr. R. I. J a f f e e a n d E. W . Collings (Battelle M e m o r i a l Institute, C o l u m b u s , Ohio) who had p r e p a r e d the m a t e r i a l s for t h e i r o w n e x p e r i m e n t s on t h e m a g n e t i c s u s c e p t i b i l i t y of t i t a n i u m a l l o y s . 3 EXPERIMENTAL
R E S U L T S A N D DISCUSSION
T h e m e a s u r e d lattice p a r a m e t e r s , with an a c c u r a c y o f ± 0 . 0 0 1 A , a r e g i v e n in T a b l e I . T a b l e I also c o n t a i n s R ~ a l l o y , a n d R ~ p u r e d e t e r m i n e d f r o m t h e 48 a n d 4 6 M . HOCH is Professor of Materials Science, University of Cincinnati, Cincinnati, Ohio. R. VISWANATHAN, formerly with the abovementioned University, is now Assistant Research Physicist, University of California, La J olla, San Diego, California. Manuscript submitted September 2 9 , 1 9 6 9 . METALLURGICAL TRANSACTIONS
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