Dislocation energetics in alpha titanium
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three y e a r s , the r e s u l t s of t h r e e m a j o r i n v e s t i g a t i o n s on low t e m p e r a t u r e d i s l o c a t i o n d y n a m ics in ot-Ti, i.e., T < 600~ have b e e n published. 1-3 Using v e r y s i m i l a r e x p e r i m e n t a l a p p r o a c h e s , i.e., the s t r a i n rate change technique, both E v a n s ~ and C o n r a d 2 a g r e e that at low t e m p e r a t u r e s d i s l o c a t i o n motion in ot-Ti is c o n t r o l l e d by a F l e i s c h e r type d i s p e r s e d b a r r i e r h a r d e n i n g 4 (probably the " t h e r m a l o v e r c o m i n g of effective oxygen i n t e r s t i t i a l s " r e g a r d l e s s of f o r e i g n atom i n t e r s t i t i a l content f r o m 100 ppm by weight to 0.3 wt pct). b2 Levine 3 i n t e r p r e t e d his s t r a i n r a t e change m e a s u r e m e n t s in zone r e f i n e d a - T i (total i n t e r s t i t i a l content ~130 ppm by wt) in t e r m s of a rate c o n t r o l ling m e c h a n i s m involving the P e i e r l s - N a b a r r o double kink n u c l e a t i o n p r o c e s s . However, S o m m e r and Ono 5 have r e c e n t l y pointed out that L e v i n e ' s a r g u m e n t s on this point a r e not well founded and his e x p e r i m e n t a l r e s u l t s at low t e m p e r a t u r e s a r e quite c o n s i s t e n t with the data s p e c t r a a n d i n t e r p r e t a t i o n developed by both C o n r a d and E v a n s . It should a l s o be noted that the pivotal e x p e r i m e n t a l r e s u l t to s u p p o r t the F l e i s c h e r h a r d e n i n g i n t e r p r e t a t i o n is the o b s e r v e d l i n e a r r e l a tion between the s q u a r e root of the " e f f e c t i v e " oxygen c o n c e n t r a t i o n 2 in the m e t a l and the t h e r m a l l y a c t i v a t e d flow s t r e s s component (~-*). In all t h r e e works, "r* at any t e m p e r a t u r e , T , and s t r a i n r a t e , ~;, was e v a l u a t e d in the usual fashion a s the d i f f e r e n c e b e tween the actual flow s t r e s s u n d e r these c o n d i t i o n s a n d the long range i n t e r n a l s t r e s s which is a s s u m e d to be the m e a s u r e d value of the flow s t r e s s at e l e v a t e d t e m p e r a t u r e for which both T* a n d d'rflow/dT equal z e r o , i.e., ~'internal i s t e m p e r a t u r e independent when c o r r e c t e d for the v a r i a t i o n of s h e a r m o d u l u s with t e m p e r a t u r e . T h u s , the F l e i s e h e r h a r d e n i n g deduetion is p a r t b a s e d on the a s s u m p t i o n that the long range i n P. P. TUNG is Graduate Student, School of Engineering, University of California, Los Angeles,Calif. A. W. SOMMER is Supervisor, Metallurgy, Los AngelesDivision,North American Rockwell Corp., Los Angeles, Calif. and Visiting Scholar Materials Division,University of California, Los Angeles. Manuscript submitted August 12, 1969. METALLURGICALTRANSACTIONS
t e r n a l s t r e s s in c~-Ti is indeed independent of t e m p e r a t u r e in the r a n g e 0~ to 600~
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