Creep of titanium-silicon alloys
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AND
M. W. MAHONEY
O p e r a t i v e c r e e p m e c h a n i s m s in l a b o r a t o r y m e l t s of T i - 5 Z r - 0 . 5 S i and T i - 5 A I - 5 Z r - 0 . 5 S i have b e e n i n v e s t i g a t e d a s a function of m i c r o s t r u c t u r e , c r e e p s t r e s s , and t e m p e r a t u r e . F r o m c r e e p r a t e d a t a a n d 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 r e s u l t s , it has been shown t h a t an i m p o r t a n t c r e e p s t r e n g t h e n i n g m e c h a n i s m at 811 K in Si b e a r i n g T i a l l o y s is c l u s t e r i n g of s o l u t e a t o m s on d i s l o c a t i o n s . A l l of the a l l o y s i n v e s t i g a t e d showed a n o m a l o u s l y high a p p a r e n t a c t i v a t i o n e n e r g i e s and a r e a s f o r c r e e p , and a high exponent (n) in t h e D o r n equation. In addition, the effect of h e a t t r e a t m e n t was i n v e s t i g a t e d and it i s shown that the h i g h e s t c r e e p s t r e n g t h was o b t a i n e d by using a heat t r e a t m e n t which r e t a i n e d the m a x i m u m a m o u n t of s i l i c o n in s o l u t i o n . T h i s is c o n s i s t e n t with the p r o p o s e d c r e e p s t r e n g t h e n i n g m e c h a n i s m . An i n v e s t i g a t i o n of the c r e e p b e h a v i o r of s e v e r a l o t h e r Si c o n t a i n i n g a l l o y s including two c o m m e r c i a l a l l o y s , T i - l l and IMI-685 i n d i c a t e d s i m i lar results.
ALTHOUGH
t i t a n i u m has a r e l a t i v e l y high m e l t i n g point (2085 K) its c r e e p r e s i s t a n c e at even m o d e r a t e t e m p e r a t u r e s (~800 K) is p o o r in c o m p a r i s o n to o t h e r e l e m e n t s . T h i s has l e d to the r e c e n t d e v e l o p m e n t of c o m p l e x t i t a n i u m a l l o y s to be u s e d f o r c o m m e r c i a l a p p l i c a t i o n s that p r o v i d e g r e a t e r c r e e p r e s i s t a n c e than o f f e r e d by e x i s t i n g c o m p o s i t i o n s . Howe v e r , the i n a b i l i t y to identify with c e r t a i n t y the m e c h a n i s m s by which c r e e p r e s i s t a n c e i s i m p a r t e d by a l l o y ing, h a s h a m p e r e d f u r t h e r d e v e l o p m e n t of c r e e p r e s i s t a n t t i t a n i u m a l l o y s . In o r d e r to i m p r o v e f u r t h e r on the c r e e p r e s i s t a n c e thus f a r a t t a i n e d it i s t h e r e f o r e n e c e s s a r y to u n d e r s t a n d the c r e e p m e c h a n i s m s which a r e r a t e c o n t r o l l i n g and the m a n n e r by which t h e s e m e c h a n i s m s m a y be e n h a n c e d . Many T i a l l o y s having good c r e e p r e s i s t a n c e cont a i n a c e r t a i n amount of Si, 1-3 and although s o m e of t h e s e a l l o y s a r e now in u s e 4 the r o l e Si p l a y s in i m p a r t ing t h e i m p r o v e d c r e e p r e s i s t a n c e i s not c l e a r . Since Si s e e m s to b e r e l a t e d to c r e e p r e s i s t a n c e it a p p e a r e d that the o b j e c t i v e s
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