Grain coarsening in Ti-5Al-2.5Sn
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aling t r e a t m e n t allowing r e c r y s t a l l i z a t i o n was noted. Tensile s p e c i m e n s r e c r y s t a l l i z e d most r a p i d l y , then drawn, r o l l e d , and c o m p r e s s e d s p e c i m e n s r e c r y s t a l l i z e d in the o r d e r l i s t e d . F o r t e n s i l e s t r a i n e d a - t i t a n i u m the dislocation m o v e ment m e c h a n i s m has, however, been hypothesized to change over the range of t e m p e r a t u r e s t e s t e d . Tung and Sommer s have a r g u e d that the d i s l o c a t i o n m e c h a nism in p u r e (A-55) a - t i t a n i u m changes at about 380 K (225~ f r o m what could be d e s c r i b e d as e i t h e r a F l e i s c h e r 6 type hardening scheme, or a P e i e r l s N a b a r r o double kink m e c h a n i s m , to a s t r a i n - a g i n g m e c h a n i s m which could involve t h e r m a l l y activated c r o s s slip at t e m p e r a t u r e s above 400 K (260~ I. EXPERIMENTAL PROCEDURE Test M a t e r i a l
BACKGROUND
REVIEW
Investigations by Bartholomew I on two g r a d e s of c o m m e r c i a l l y pure a - t i t a n i u m have d e m o n s t r a t e d the r e l a t i o n s h i p between the d e g r e e of deformation at room t e m p e r a t u r e and the annealing t e m p e r a t u r e s and t i m e s r e q u i r e d for r e c r y s t a l l i z a t i o n . Bartholomew also s t a t e d that r e c r y s t a l l i z a t i o n and grain c o a r s e n i n g were a c c o m p l i s h e d by g r a i n boundary m i g r a t i o n . S i m i l a r work has been done by W i l l i a m s and E b o r a l l 2 with s e v e r a l a l u m i num a l l o y s . Decker, et al, s in studying seven different high t e m p e r a t u r e alloys, used t e n s i l e s t r a i n i n g and r o l l i n g to induce r e c r y s t a l l i z a t i o n . While they l i s t e d the values of s t r a i n c o r r e s p o n d i n g to c r i t i c a l coldwork causing r e c r y s t a l l i z a t i o n for the v a r i o u s t e m p e r a t u r e s at which t h e i r m a t e r i a l s were c o l d - w o r k e d (or w a r m - w o r k e d ) , they were unable to develop a method of p r e d i c t i n g the c r i t i c a l s t r a i n at a given t e m p e r a t u r e b a s e d on the c r i t i c a l s t r a i n s at other t e m p e r a t u r e s . They did, however, note that t h e r e was frequently a d e c r e a s e in deformation r e q u i r e d for g r a i n c o a r s e n ing with an i n c r e a s e in the t e m p e r a t u r e at which the d e f o r m a t i o n took p l a c e . Barto and E b e r t 4 have d e m o n s t r a t e d that the d e f o r mation m e c h a n i s m (tension, drawing, rolling, and c o m p r e s s i o n ) influences r e c r y s t a l l i z a t i o n k i n e t i c s in m o lybdenum. When equivalent cold-work, as m e a s u r e d by t r u e s t r a i n , was done, significant d i f f e r e n c e s in the THOMAS K. MOORE, Major, USAF, is a Structural MaterialsApplications Engineer, Strength Branch, Directorate of Airframe Engineering, AeronauticalSystemsDivision,Wr
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