Creep resistance and high-temperature metallurgical stability of titanium alloys containing gallium
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Creep Resistance and High-Temperature Metallurg icoJ Stability of Titanium Alloys Containing Gallium C. E. SHAMBLEN AND T. K. REDDEN T e n s i l e p r o p e r t i e s up to l l 0 0 ~ and the c r e e p r e s i s t a n c e at 1000~ w e r e c o r r e l a t e d with c o m p o s i t i o n f o r t w e l v e c o m p l e x d e v e l o p m e n t a l t i t a n i u m a l l o y s with a d d i t i o n s of A1, Ga, Sn, Mo, Z r , and Si. C r e e p r e s i s t a n c e for t h e s e a l l o y s in the ~ h e a t - t r e a t e d condition w a s found to b e s t r o n g l y dependent on the t o t a l a s t a b i l i z e r content and t h e s i l i c o n c o n c e n t r a tion. The c r e e p a c t i v a t i o n e n e r g y f o r a T i - 4 . 5 A1-2 Sn-3 Z r - 3 Ga-1 M o - 0 . 5 Si a l l o y , e s t a b l i s h e d o v e r the 900 ~ to l l 0 0 ~ t e m p e r a t u r e r a n g e , w a s about 100 k c a l p e r g - m o l e . T h i s high c r e e p a c t i v a t i o n e n e r g y i s h y p o t h e s i z e d to r e s u l t f r o m d i s p e r s i o n s t r e n g t h e n i n g within the m a t r i x by the Ti3X (X = A1, Ga, Sn) p h a s e and pinning of the i n t e r p l a t e l e t and p r i o r g r a i n b o u n d a r i e s by the ZrsSi3 p h a s e . Both p h a s e s w e r e i d e n t i f i e d by t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y in t h e s e r e s p e c t i v e l o c a t i o n s . M e t a l l u r g i c a l i n s t a b i l i t y , a s e v i d e n c e d by d e c r e a s e d f r a c t u r e t o u g h n e s s , i s a l s o shown to be r e l a t a b l e to the t o t a l a s t a b i l i z e r cont e n t . The a c t i v a t i o n e n e r g y f o r the e m b r i t t l e m e n t p r o c e s s i s a b o u t 45 k c a l p e r g - m o l e . which a p p r o x i m a t e s that f o r i n t e r d i f f u s i o n of g a l l i u m in a t i t a n i u m .
T H E m e c h a n i c a l p r o p e r t i e s of c o m m e r c i a l and r e cent d e v e l o p m e n t a l l o y s i n d i c a t e that t h e next g e n e r a tion of h i g h - t e m p e r a t u r e (800 ~ to 1200~ t i t a n i u m a l l o y s will b e b a s e d on the s i l i c o n b e a r i n g , n e a r - ~ s y s t e m . The m a j o r t e c h n i c a l p r o b l e m f o r t h i s s y s t e m i s a c h i e v i n g h i g h - t e m p e r a t u r e s t r e n g t h without s i g n i f i cantly c o m p r o m i s i n g m e t a l l u r g i c a l s t a b i l i t y . M e t a l l u r g i c a l s t a b i l i t y i s defined a s the a b i l i t y to r e t a i n a d e q u a t e low t e m p e r a t u r e t o u g h n e s s a f t e r l o n g - t i m e t h e r m a l e x p o s u r e at 800 ~ to 1200~ The embrittlement of t h e s e a l l o y s is b e l i e v e d to b e a s s o c i a t e d with the Ti3X p h a s e , w h e r e X d e s i g n a t e s the a s t a b i l i z i n g e l e m e n t s AI, Ga, and Sn. C r o s s l e y and C a r e w ~ i n i t i a l l y r e p o r t e d t h i s t y p e of e m b r i t t l e m e n t f o r a T i - 8 wt p c t A1 a l l o y in 1957. T h i s b e h a v i o r w a s c o n f i
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