The effect of processing on plastic anisotropy of Ti-6Al-4V
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,-r J.HERE h a s b e e n c o n s i d e r a b l e i n t e r e s t r e c e n t l y in the u s e of t e x t u r e d t i t a n i u m a l l o y s h e e t f o r p r e s s u r e v e s s e l a p p l i c a t i o n s . T h i s is b e c a u s e of the l a r g e amount of b i a x t a l s t r e n g t h e n i n g a c h i e v e d when the t h r o u g h t h i c k n e s s s t r a i n is m i n i m i z e d by the s h e e t t e x t u r e . The a m o u n t of t e x t u r e s t r e n g t h e n i n g d e p e n d s upon the d e g r e e of p l a s t i c a n i s o t r o p y d e v e l o p e d in the m a t e r i a l . Much of the w o r k in t e x t u r e d t i t a n i u m m a t e r i a l s h a s b e e n on a l l - a l p h a a l l o y s , such a s T i - 5 A1-2.5 Sn 1-3 and T i - 4 A1-0.25 O, %3 o r c o m m e r c i a l l y p u r e t i t a n i u m . 4-8 The t o t a l l y h e x a g o n a l s t r u c t u r e of t h e s e m a t e r i a l s m a k e s t h e m m o s t s u s c e p t i b l e to t e x t u r e s t r e n g t h e n i n g . I n t e r e s t in the t e x t u r e s t r e n g t h e n i n g b e h a v i o r of the a l p h a - b e t a a l l o y T i - 6 A1- 4 V h a s d e v e l o p e d b e c a u s e of i t s c o n s i d e r a b l e i m p o r t a n c e in s t r u c t u r a l a p p l i c a t i o n s . This m a t e r i a l h a s been s t u d i e d m a i n l y in the m i l l - a n n e a l e d condition. %s-7 H o w e v e r , knowledge of the p l a s t i c a n i s o t r o p y of T i - 6 A1-4 V in a v a r i e t y of p r o c e s s i n g c o n d i t i o n s is r e q u i r e d f o r e v a l u a t i o n of its full p o t e n tial for texture-strengthened pressure vessels. An index of a n t s o t r o p y R often p r e s e n t e d in the l i t e r a t u r e is the r a t i o s of the width s t r a i n to the t h i c k n e s s s t r a i n . The R v a l u e f o r m i l l - a n n e a l e d T i - 6 A 1 4 V s h e e t i s g e n e r a l l y l e s s than 1, i n d i c a t i n g b i a x i a l softening, 2'8 but R v a l u e s g r e a t e r than 1 have b e e n r e p o r t e d f o r t h i s m a t e r i a l . L a r g e r v a r i a t i o n s in a n i s o t r o p y have b e e n noted a m o n g h e a t s with d i f f e r e n t but unknown p r o c e s s i n g h i s t o r i e s . 7 A n t s o t r o p y in a l l - a l p h a m a t e r i a l s is s e n s i t i v e to p r o c e s s i n g h i s t o r i e s , 1-6 and s i m i l a r v a r i a t i o n s a r e not u n e x p e c t e d in T i - 6 A1-4 V. In t h i s w o r k , the effect of p r o c e s s i n g t r e a t m e n t s on T i - 6 A1-4 V a l l o y s was s t u d i e d . T h e r m a l t r e a t m e n t s , r o l l i n g , and f o r g i n g in both the b e t a and the a l p h a - b e t a r e g i o n s w e r e a p p l i e d . The r e s u l t i n g d i f f e r e n c e s in t e x t u r e , s t r e n g t h , and p l a s t i c s t r a i n a n t s o t r o p y a r e described.
M. F. AMATEAU, D. L. DULL, and L. RAYMOND are Manager, Metal Composites, Member of the Technical Staff, and Manager, Metallurgical Research, respectively, Materials Science
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