Deformation of Nb-W single crystals: Athermal solid solution strengthening
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t e m p e r a t u r e substitutional s o l i d s o l u t i o n h a r d e n i n g in b c c a l l o y s is c o m p l i c a t e d b y the fact that the flow s t r e s s c o n s i s t s of b o t h t h e r m a l l y a c t i v a t e d a n d a t h e r m a l c o m p o n e n t s . It is g e n e r a l l y a c c e p t e d that the flow s t r e s s is e q u a l to the s i m p l e s u m of the a t h e r m a l c o m p o n e n t , 7i, a n d the t h e r m a l l y a c t i v a t e d c o m p o n e n t , T*.I In o r d e r to u n d e r s t a n d substitutional s o l i d s o l u tion h a r d e n i n g in b c c a l l o y s , e a c h c o m p o n e n t m u s t b e a n a l y z e d individually. T h e p u r p o s e of the p r e s e n t note is to e x a m i n e b o t h the t e c h n i q u e s of o b t a i n i n g the a t h e r m a l c o m p o n e n t a n d the n a t u r e of this s t r e s s c o m p o n e n t in substitutional, s o l i d s o l u t i o n s t r e n g t h e n e d N b - W s i n g l e c r y s t a l s . S i n c e e a c h of the s o l i d s o l u t i o n s t r e n g t h e n i n g t h e o r i e s 2-8 p r e d i c t s that the r e s u l t a n t s t r e n g t h e n i n g d e p e n d s o n the s o l u t e c o n c e n t r a t i o n in a s p e c i f i c m a n n e r , a c c u r a t e d e t e r m i n a t i o n of c o m p o s i t i o n a l d e p e n d e n c e of 7 i s h o u l d test e a c h t h e o r y ' s v a lidity. A l t h o u g h s t u d i e s9' io h a v e b e e n p e r f o r m e d o n the a t h e r m a l d e f o r m a t i o n of n o n f e r r o u s b c e a l l o y s i n g l e c r y s t a l s , o n l y K o s t o r z 1 1 h a s a t t e m p t e d to e x a m i n e the c o m p o s i t i o n a l d e p e n d e n c e of 7 i . W o r k i n g w i t h b i n a r y a l l o y s of N b - T a , N b - V , a n d N b - W (up to 6 pct W ) , K o s t o r z o b s e r v e s that the a t h e r m a l s t r e s s is l i n e a r l y d e p e n d e n t o n s o l u t e c o n c e n t r a t i o n in the N b - W a l l o y s but p a r a b o l i c a l l y d e p e n d e n t in N b - V a n d N b - T a a l l o y s . T h i s s t u d y e x a m i n e s N b - W a l l o y c r y s t a l s at c o m p o s i t i o n s u p to N b - 1 5 pet W , a n d p r e s e n t s d a t a o b t a i n e d b o t h b y the r e l a x a t i o n t e c h n i q u e d u e to L i 12 a n d b y the c o m m o n l y u s e d m e t h o d utilizing the t e m p e r a t u r e d e p e n d e n c e of the flow s t r e s s . MATERIALS
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T h e s i n g l e c r y s t a l s u s e d in this s t u d y w e r e g r o w n b y t w o p a s s e s in a n e l e c t r o n b e a m z o n e r e f i n i n g a p p a r a t u s o p e r a t i n g a t a v a c u u m o f a b o u t 10 -~ t o r r . A l l s p e c i m e n s w e r e of t h e s a m e s i n g l e g l i d e o r i e n t a t i o n n e a r l y on t h e z o n e a x i s f o r [ 1 1 1 ] ( [ 0 1 ) s l i p . S i n c e o n l y flow s t r e s s d a t a a t s m a l l s t r a i n s ( a x i a l s t r a i n s o f 0.02 t o 0 . 0 7 ) w a s r e q u i r e d ,
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