The effects of second-phase dispersoids on the deformation behavior of titanium
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o r d e r p e r s i s t s above T c in a l l o y s with o r d e r - d i s o r d e r t r a n s f o r m a t i o n s . 14'1s Like the d e g r e e of long r a n g e o r d e r , the d e g r e e of s h o r t r a n g e o r d e r a l s o depends on the t e m p e r a t u r e and c o m p o s i t i o n . ~6 By c o m p a r i n g the v a r i a t i o n of M s t e m p e r a t u r e above T c for both c o m p o s i t i o n s , we s u g g e s t that the d e g r e e of s h o r t r a n g e o r d e r in the o f f - s t o c h i o m e t r i c alloy is m o r e t e m p e r a t u r e d e p e n d e n t than it is in the n e a r - s t o c h i o m e t r i c alloy.
The Effects of Second-Phase Dispersoids on the Deformation Behavior of Titanium
T o q u a n t i t a t i v e l y a s s e s s the effects of oxygen s c a v enging by the e r b i u m and y t t r i u m a d d i t i v e s , and to d i f f e r e n t i a t e the effects of the d i s p e r s o i d s and i n t e r s t i t i a l oxygen on the d e f o r m a t i o n b e h a v i o r of t i t a n i u m , the t e m p e r a t u r e d e p e n d e n c e of the y i e l d s t r e s s of t i t a n i u m and T i - E r and T i - Y a l l o y s was d e t e r m i n e d f r o m 77 to 625 K. The Orowan s t r e s s was c a l c u l a t e d f r o m the m e a s u r e d v a l u e s of the d i s p e r s e d - p h a s e p a r a m e t e r s in the T i - E r and T i - Y a l l o y s , and the i n t e r s t i t i a l - o x y g e n s t r e n g t h e n i n g was d e t e r m i n e d f r o m a m e a s u r e m e n t of the d e p e n d e n c e of the flow s t r e s s of t i t a n i u m on the oxygen c o n c e n t r a t i o n . The e x p e r i m e n t a l l y d e t e r m i n e d f l o w - s t r e s s v a l u e s were then a n a l y z e d on the b a s i s of the s u p e r p o s i t i o n of the two s t r e n g t h e n i n g m e c h a n i s m s at d i f f e r e n t t e m p e r a t u r e s , taking into a c count the r e d u c t i o n in the flow s t r e s s c a u s e d by oxygen scavenging. T i t a n i u m ingots with the oxygen, e r b i u m , and y t t r i u m c o n c e n t r a t i o n s l i s t e d in T a b l e I w e r e p r e p a r e d by n o n c o n s u m a b l e - e l e c t r o d e v a c u u m a r c - m e l t i n g and were hot r o l l e d to 3 m m f i n a l t h i c k n e s s . T e n s i l e s p e c i m e n s m a c h i n e d f r o m the r o l l e d s h e e t s w e r e a n n e a l e d at 873 to 1123 K in an a t m o s p h e r e of d r y a r g o n to produce fully r e c r y s t a l l i z e d m i c r o s t r u c t u r e s . T e n s i l e t e s t s w e r e p e r f o r m e d at 77, 295, 450, and 625 K at a s t r a i n r a t e of 3 • 10 -4 s -1. The d i s p e r s e d phase p a r a m e t e r s were determined from t r a n s m i s s i o n electron microscopic e x a m i n a t i o n of thin foils and e x t r a c t i o n r e p l i c a s p r e p a r e d f r o m the a n n e a l e d s h e e t s . The t e m p e r a t u r e
K. K. SANKARAN, P. S. PAO
S. M. L. SASTRY,
AND
A d d i t i o n s of s m a l l a m o u n t s of e r b i u m and y t
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