The effect of ternary additions on the decompositon of metastable beta-phase titanium alloys
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elevated t e m p e r a t u r e a l l o t r o p i c f o r m of tit a n i u m is designated the B phase and can be r e t a i n e d in a m e t a s t a b l e condition at r o o m t e m p e r a t u r e in quenched alloys which contain s u i t a b l e c o n c e n t r a t i o n s of such e l e m e n t s as m o l y b d e n u m o r v a n a d i u m . S u b s e q u e n t aging of the m e t a s t a b l e B phase r e s u l t s in the f o r m a t i o n of the e q u i l i b r i u m a phase o r the m e t a s t a b l e w phase dependent on aging t e m p e r a t u r e and t i m e . F o r m a t i o n of the a phase p r o v i d e s the b a s i s for the h e a t - t r e a t a b l e c o m m e r c i a l B-phase a l l o y s , w h e r e a s f o r m a t i o n of the w phase is g e n e r a l l y c o n s i d e r e d u n d e s i r a b l e since it can r e s u l t in s e v e r e e m b r i t t l e m e n t of the a l l o y s . Recent work on the b i n a r y T i - V and T i - M o s y s t e m s has e s t a b l i s h e d much m o r e c l e a r l y the c o n d i t i o n s u n d e r which the a and w phases a r e f o r m e d and h a s e n a b l e d the c o n s t r u c t i o n of m e t a s t a b l e phase d i a g r a m s f o r these b i n a r y s y s t e m s . ~-s F r o m such d i a g r a m s the t e m p e r a t u r e range of s t a b i l i t y and the c o m p o s i t i o n s of the wand /3 p h a s e s can be s p e c i f i e d . The w phase can occur as e i t h e r c u b i c a l or e l l i p s o i dal p r e c i p i t a t e s and in b i n a r y s y s t e m s the morphology and the t i m e - t e m p e r a t u r e l i m i t s of s t a b i l i t y have been c o r r e l a t e d with the m i s f i t between the p r e c i p i t a t e and m a t r i x . 4'5 Since the B phase in the c o m m e r c i a l a +/3 and B-phase a l l o y s is always at l e a s t a t e r n a r y phase, the types of s t u d i e s m e n t i o n e d above f o r b i n a r y s y s t e m s need to be extended to t e r n a r y a l l o y s . In the p r e s e n t work we have studied the effect of t e r n a r y alloying additions of A1, Sn, Z r , and O on the d e c o m p o s i tion m e c h a n i s m s of T i - V and T i - M o a l l o y s . T h e s e e l e m e n t s a r e the m o s t c o m m o n a l l o y i n g a d d i t i o n s to c o m m e r c i a l a l l o y s , o t h e r than the B - s t a b i l i z i n g e l e m e n t s m o l y b d e n u m and v a n a d i u m t h e m s e l v e s . L i m i t e d w o r k has b e e n p u b l i s h e d on the effect of t e r n a r y additions o n w - p h a s e f o r m a t i o n , but the studies are l a r g e l y qualitative in n a t u r e . Weygand and D o r s t 6 studied the effect of a l u m i n u m additions on a T i - 9 pct C r alloy and found that i n c r e a s i n g a l u m i n u m content r e d u c e d the volume f r a c t i o n of w phase, de-
J. C. WILLIAMSis Group Leader, Physical Metallurgy, North American Rockwell Science Center, Thousand Oaks, Calif. B. S. HICKMAN, formerly with North American Rockwell Science Center, is Director of Researc
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