Comparison of first quadrant yield loci for Ti-6Al-4V with those predicted by knoop hardness measurements
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Communications Comparison of FirstQuadrant Yield Loci for Ti-6AI-4V With Those Predicted by Knoop Hardness Measurements
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M. F. AMATEAU AND W. D. HANNA The d i r e c t m e a s u r e m e n t of a b i a x i a l yield locus is a difficult e x p e r i m e n t a l p r o c e d u r e and, t h e r e f o r e , m o r e expedient a l t e r n a t i v e methods have b e e n suggested. 1, 2 One technique, which is of p a r t i c u l a r i n t e r e s t b e c a u s e of its r e l a t i v e s i m p l i c i t y and s m a l l s a m p l e size r e q u i r e m e n t , is b a s e d on the a n i s o t r o p y of Knoop h a r d n e s s i m p r e s s i o n s , s R e a s o n a b l e a g r e e m e n t has b e e n r e p o r t e d for s e l e c t e d alloys of m a g n e s i u m , z i r c o n i u m , and t i t a n i u m when loci c o n s t r u c t e d b y this method a r e c o m p a r e d to a r e s t r i c t e d p o r t i o n of m e a s u r e d yield loci or to those d e t e r m i n e d at l a r g e p l a s t i c s t r a i n s . Lack of c o r r e l a t i o n has o c c u r r e d p r i m a r i l y b e c a u s e of f a i l u r e to p r e d i c t a s y m m e t r y of the loci i n v e s t i gated. 4,s A study was u n d e r t a k e n to explore the use of this technique in the alloy T i - 6 A1-4 V over a r a n g e of a n i s otropic conditions. Biaxial yield loci c o n s t r u c t e d f r o m Knoop h a r d n e s s i m p r e s s i o n s were c o m p a r e d with p a r t i a l yield loci in the f i r s t q u a d r a n t as d e t e r m i n e d f r o m flow s t r e s s m e a s u r e m e n t s at t h r e e s t r e s s r a t i o s . The T i - 6 A1-4V contained 0.23 pct C, 0.6 pct Fe, 0.11 pct O, 5.8 pct A1, and 4.0 pct V. V a r i o u s d e g r e e s of p l a s t i c anisotropy were introduced by unidirectionally rolling the i n i t i a l 3 . 8 - m m sheet to a t h i c k n e s s of 1.9 m m at r o o m t e m p e r a t u r e and 1030, 1210, and 1340 K and b y c r o s s r o l l i n g at r o o m t e m p e r a t u r e . M a t e r i a l in sheet f o r m for both m i l l - a n n e a l e d and s o l u t i o n - t r e a t e d and aged (STA) conditions was also e x a m i n e d . A wide v a r i e t y of t e x t u r e s r e s u l t e d f r o m t h e s e t r e a t m e n t s , as was v e r i f i e d b y pole f i g u r e a n a l y s i s which is p r e s e n t e d elsewhere 6 A m i n i m u m of t h r e e u n i a x i a l t e n s i l e t e s t s were made in the l o n g i t u d i n a l and t r a n s v e r s e d i r e c t i o n s of the sheets to d e t e r m i n e the 1:0 and 0:1 r a t i o yield s t r e s s e s . The 1:1 r a t i o yield s t r e s s was e s t a b l i s h e d by duplicate c o m p r e s s i v e t e s t s of the sheet t h i c k n e s s , u s i n g the stacked disk method d e s c r i b e d by Babel and Corn. 7 The yield point of each t e s t and the p l a s t i c a n i s o t r o p y r a t i o s R and P were d e t e r m i n e d at a p l a s t i c s t r a i n of 0.002. The a v e r a g e v a l u e s f r o m t h e s
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