Effect of composition, microstructure, and texture on stress-corrosion cracking in Ti-61-4V sheet
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have b e e n n u m e r o u s s t u d ie s of s t r e s s - c o r r o s i o n c r a c k i n g (SCC) in t i t a n i u m a l l o y s . ( T h r e e e x t e n s i v e r e v i e w s a r e contained in R e f s . 1 to 3. T h e y have p r o v i d e d an insight into the s t r e s s - c o r r o s i o n p h e n o m e n o n and have r e s u l t e d in c h a r a c t e r i z a t i o n of it f o r n u m e r o u s a l l o y s and m i c r o s t r u c t u r e s . A s a r e s u l t , the SCC t h r e s h o l d is n o m i n a l l y defined f o r given heat t r e a t m e n t s and c o m p o s i t i o n s , but the data s c a t t e r is quite b r o a d . T h i s s c a t t e r r e s u l t s in low d e s i g n m i n i m u m v a l u e s f o r the s t r e s s - c o r r o s i o n t h r e s h o l d and s u b s e q u e n t weight p e n a l t i e s f o r f r a c t u r e - c r i t i c a l p a r t s . T h i s study was u n d e r t a k e n to a t t e m p t to define the key p a r a m e t e r s c o n t r o l l i n g the SCC t h r e s h o l d f o r T i - 6 A 1 - 4 V sheet, to d e t e r m i n e the magnitude of t h e i r e f f e c t s , and to d e r i v e an equation f o r p r e d i c t i n g the SCC t h r e s h o l d (K SCC) in t e r m s of t h e s e p a r a m e t e r s . D e t e r m i n a t i o n of the key m e t a l l u r g i c a l v a r i a b l e s aff e c t i n g KSCC can lead to the u p g r a d i n g of T i - 6 A 1 - 4 V d e s i g n v a l u e s f o r KSCC th r o u g h i m p r o v e d p r o c e s s cont r o l in m e l t i n g and m i l l p r o c e s s i n g . L i n e a r r e g r e s s i o n a n a l y s e s w e r e u s e d to c o r r e l a t e KSCC data f r o m 46 heats of d u p l e x - a n n e a l e d s h e e t with the s e l e c t e d p a r a m e t e r s : m i c r o s t r u c t u r e , c o m p o s i t i o n , and t e x t u r e . Th e l i n e a r r e g r e s s i o n a n a l y s e s p r o ~ d e an e c o n o m i c m e a n s of s o r t i n g out dominant v a r i a b l e s on a s t a t i s t i c a l b a s i s f r o m p r o d u c t i o n m a t e r i a l , as opposed to a r e s e a r c h e f f o r t that would r e q u i r e m e l t i n g and p r o c e s s i n g of n u m e r o u s ingots in w h i c h one p a r a m e t e r is v a r i e d while a t t e m p t i n g to hold o t h e r p a r a m e t e r s co n s t a n t. E x t e n s i v e p r o p e r t y and m e t a l l u r g i c a l data w e r e a c c u m u l a t e d f r o m e a c h heat of m a t e r i a l so that c o m p r e h e n s i v e a n a l y s e s could be p e r f o r m e d . M i c r o s t r u c r u r a l p a r a m e t e r s included p r i m a r y a lp h a g r a i n s i z e , p e r c e n t p r i m a r y alpha, alpha g r a i n shape (aspect r a t i o ) , and d e g r e e of o r d e r i n g in alpha. P a r a m e t e r s used to i n d i c a t e v a r i a t i o n s in t e x t u r e included ATYS,
ATUS, and K A , which is d e r i v e d f r o m an X - r a y pole f i g u r e . Sheet gage was a I s o included to n o r m a l i z e the d i f f e r e n c e s of t h i c k n e s s f r o m the 46 m
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