Fracture toughness and deformation of titanium alloys at low temperatures
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AND
W. D. HANNA
E x p e r i m e n t a l data c o n c e r n i n g the influence of c o m p o s i t i o n a l , m i c r o s t r u c t u r a l and t e x t u r a l v a r i a t i o n s on the f r a c t u r e t o u g h n e s s and d e f o r m a t i o n k i n e t i c s of o~ and a - ~ t i t a n i u m a l l o y s a r e p r e s e n t e d . In p a r t i c u l a r , the influence of these p a r a m e t e r s on the t h e r m a l and a t h e r m a l c o m p o n e n t s of the flow s t r e s s is c o m p a r e d to t h e i r influence on f r a c t u r e toughness. The s i m i l a r i t i e s in d e f o r m a t i o n b e h a v i o r a m o n g a l l o y s a r e noted and c o n t r a s t e d to the d i s s i m i l a r i t i e s in f r a c t u r e toughness b e h a v i o r . I N r e c e n t y e a r s , g r e a t p r o g r e s s has b e e n made tow a r d s u n d e r s t a n d i n g the d e f o r m a t i o n b e h a v i o r of m e t a l s . Recent y e a r s have also seen s u b s t a n t i a l gains in the development of f r a c t u r e m e c h a n i c s as a t e c h nique to deal with the p r o b l e m of f r a c t u r e toughness. Rather s u r p r i s i n g , however, is the r e l a t i v e l y s m a l l effort that has b e e n expended r e l a t i n g d e f o r m a t i o n b e havior to f r a c t u r e toughness. It is quite c l e a r that the two m u s t in some way be r e l a t e d , for it i s known that p l a s t i c d e f o r m a t i o n can affect c r a c k p r o p a g a t i o n , both by the a b s o r p t i o n of e n e r g y and by a r e d u c t i o n in the s t r e s s c o n c e n t r a t i o n at the tip of a c r a c k . However, the development of specific r e l a t i o n s i s not a t r i v i a l t a s k , and has b e e n h i n d e r e d by the difficulty of obtaining an a n a l y t i c a l solution for s t r e s s e s and s t r a i n s in the v i c i n i t y of flaws. T h i s difficulty i s compounded when a m a t e r i a l with a n i s o t r o p i c p r o p e r t i e s m u s t be c o n s i d e r e d . On this b a s i s , c o m m e r c i a l a l l o y s of hexagonal a t i t a n i u m would not seem to be a good m a t e r i a l to use in s t u d i e s a t t e m p t i n g to r e l a t e d e f o r m a t i o n b e h a v i o r to f r a c t u r e toughness. However, in the p r e s e n t study, technological c o n s i d e r a t i o n s o v e r r o d e those of e x p e r i m e n t a l convenience and this m a t e r i a l was chosen for the exp e r i m e n t a l work. As a r e s u l t , the data and o b s e r v a t i o n s p r e s e n t e d in this paper lack the c o m p l e t e n e s s and detail u s u a l l y found in a f u n d a m e n t a l study. On the other hand, the i n f o r m a t i o n p r e s e n t e d does show which p a r a m e t e r s of d e f o r m a t i o n b e h a v i o r a r e s i g n i f i c a n t to the f r a c t u r e toughness of t i t a n i u m a l l o y s . It is hoped that such i n f o r m a t i o n will f u r t h e r the u n d e r s t a n d i n g of f r a c t u r e toughness and lead to the d e v e
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