Texture strengthening and strength differential in titanium-6Al-4V
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the e x a m i n a t i o n of yield loci and m i c r o s t r u c t u r e s we have a t t e m p t e d to d e t e r m i n e the potential which e x i s t s for t e x t u r e s t r e n g t h e n i n g in the alloy, and to a n a l y z e the m e c h a n i s m s of the d e f o r m a t i o n p r o c e s s .
EXPERIMENTAL
PROCEDURE
D u r i n g an e a r l i e r stage of this work, 13 the d e v e l o p m e n t of t e x t u r e was studied in T i - 6 A1-4 V under v a r y ing conditions of d e f o r m a t i o n , r e c r y s t a l l i z a t i o n and p h a s e t r a n s f o r m a t i o n . On the b a s i s of this work, six b a t c h e s of m a t e r i a l were produced for yield loci d e t e r m i n a t i o n s with d i f f e r e n t t e x t u r e s but n o m i n a l l y s i m i l a r m i c r o s t r u c t u r e s . Two of t h e s e b a t c h e s (denoted A and B) which r e p r e s e n t e d e x t r e m e s in the r a n g e of t e x t u r e s will be d e s c r i b e d h e r e . The m e c h a n i c a l p r o p e r t i e s of the o t h e r s were i n t e r m e d i a t e b e t w e e n these two. Pole figures of the {0002}, {1010} and {i011} reflections were measured using a Siemens texture goniometer with filtered Cr Kce radiation. The sectioning method of Lopata and KulaI~ was used to obtain a complete quadrant of the pole figure and normalization was achieved by comparison with the reflected intensity from a very nearly random sample of commercial purity titanium. For the determination of yield loci the method of Lee and Backofen is was followed u s i n g t e n s i o n , c o m p r e s s i o n , and plane s t r a i n c o m p r e s s i o n t e s t s to obtain proof s t r e s s v a l u e s . The nine loading conditions used a r e shown in Fig. 1. Length and width s t r a i n s on the t e n s i l e s p e c i m e n s were m e a s u r e d u s i n g l i n e a r v o l t a g e d i s p l a c e m e n t t r a n s d u c e r s with a r e s o l u t i o n of b e t t e r than 10 -s c m s . A s i m i l a r t r a n s d u c e r was used to o b t a i n v a l u e s of d i s p l a c e m e n t in the jig b u i l t for s i m p l e and p l a n e s t r a i n c o m p r e s s i o n t e s t s . The s p e c i m e n s w e r e loaded u s i n g a 10,000 Kg I n s t r o n m a c h i n e and the l o a d e x t e n s i o n c u r v e s were plotted a u t o m a t i c a l l y on an X - Y r e c o r d e r . In all c a s e s the i n i t i a l s t r a i n r a t e s w e r e b e tween 0.02 and 0.04 per m i n . A n u m b e r of t e s t s were c a r r i e d out i n i t i a l l y to find conditions f r e e f r o m s y s t e m a t i c e r r o r . As a r e s u l t of this, the s i m p l e c o m p r e s sion s p e c i m e n s were d e s i g n e d with a s q u a r e c r o s s s e c t i o n and a height to t h i c k n e s s r a t i o of 2.5. S i m i l a r l y , the plane s t r a i n c o m p r e s s i o n s a m p l e s ( F o r d test) w e r e made so that the r a t i o of i n d e n t o r t h i c k n e s s to s p e c i m e n t h i c k n e s s was ~ 2 and the s p e c i m e n width was
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