Deformation mechanisms in commercial Ti (0.5 at. pct oineq) at intermediate and high temperatures (0.3 - 0.6 tinm)
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m e c h a n i c a l b e h a v i o r of a - t i t a n i u m at t e m p e r a t u r e s b el o w 0.3T m has b e e n e x t e n s i v e l y s tu d i e d by C o n r a d and c o w o r k e r s , h2 As a r e s u l t of t h e i r w o r k it has now b e e n f i r m l y e s t a b l i s h e d that in this t e m p e r a t u r e r e g i m e the r a t e c o n t r o l l i n g d i s l o c a t i o n m e c h a n i s m in p l a s t i c flow ( t h e r m a l c o m p o n e n t of the flow s t r e s s ) is the t h e r m a l l y a c t i v a t e d o v e r c o m i n g of i n t e r s t i t i a l s o l u t e o b s t a c l e s on f i r s t o r d e r p r i s m p l a n e s . The e f f e c t s of s t r a i n , g r a i n s i z e and i n t e r s t i t i a l content on the a t h e r m a l c o m p o n e n t of the flow s t r e s s was found to be t h r o u g h the d i s l o c a t i o n d e n s i t y p r o d u c e d d u r i n g s t r a i n i n g , which l e a d s to a l o n g - r a n g e i n t e r n a l s t r e s s opposing d i s l o c a t i o n motion. Little is, h o w e v e r , known about the d e f o r m a t i o n m e c h a n i s m s above 0.3T m. The w o r k of R e e d - H i l l and c o w o r k e r s 3-5 i n d i c a t e s that d y n a m i c s t r a i n aging o c c u r s in c o m m e r c i a l p u r i t y m a t e r i a l b e t w e e n 0.3 to 0.4T m. This is a l s o i n d i c a t e d by the e n h a n c e m e n t of c r e e p s t r e n g t h 6,7 and h i g h - c y c l e , l o n g - l i f e fatigue p r o p e r t i e s 8 in this t e m p e r a t u r e r a n g e . Although it has b e e n e s t a b l i s h e d that i n t e r s t i t i a l s o l u t e s a r e r e s p o n s i b l e f o r t h i s b e h a v i o r , the e x a c t d e t a i l s of the p r o c e s s a r e not ye t c l e a r . As fo r the m e c h a n i c a l b e h a v i o r above 0.4 to 0.5Tin, w h e r e a diffusion c o n t r o l l e d d e f o r m a t i o n m e c h a n i s m is e x p e c t e d to be r a t e c o n t r o l l i n g , p r a c t i c a l l y nothing is known. The p u r p o s e of this study was t h e r e f o r e to identify the r a t e c o n t r o l l i n g m e c h a n i s m s d u r i n g p l a s t i c d e f o r m a t i o n of a ~ t i t a n i u m at t e m p e r a t u r e s above 0.3T m . The m a t e r i a l c h o s e n was c o m m e r c i a l T i - 5 0 A , b e c a u s e of the v a r i o u s u n a ll o y e d c o m m e r c i a l t i t a n i u m m a t e r i a l s it is i n t e r m e d i a t e in i n t e r s t i t i a l content (which is a l s o the c a s e f o r many t i t a n i u m a ll o y s ) and b e c a u s e a d e t a i l e d study was c o n c u r r e n t l y u n d e r w a y into the m e c h a n i c a l b e h a v i o r of this m a t e r i a l at low t e m p e r a t u r e s f It is planned to define in d e t a i l the s t r e n g t h e n i n g m e c h a n i s m s of T1-50A f r o m 0 K to the a ~ fi t r a n s i t i o n t e r n -
M. DONER and H. CONRAD are Research Associate, and Professor and Chairman at Metallurgical Engineering and Materials Science Department, University of
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