Plastic deformation of Ni-Cr single crystals
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A l a r g e n u m b e r of e l e c t r i c a l r e s i s t a n c e a n d t h e r m o c o u p l e m a t e r i a l s a s w e l l a s s u p e r a l l o y s of t e c h n o l o g i c a l i m p o r t a n c e a r e n i c k e l - b a s e a l l o y s c o n t a i n i n g up t o 22 p c t C r w i t h o r w i t h o u t o t h e r a l l o y i n g a d d i t i o n s . N i c k e l d i s s o l v e s a p p r o x i m a t e l y 33 a t p c t C r i n s o l i d s o l u t i o n a t 2 9 5 ° K .* T h e physical and mechanical properties of N i - C r s o l i d s o l u t i o n s do not v a r y w i t h t e m p e r a t u r e a n d t h e r m a l h i s t o r y in t h e w a y n o r m a l l y e x p e c t e d f o r s i m p l e solutions. 2 T h e mechanical properties of p o l y c r y s t a l l i n e a l l o y s c o n t a i n i n g up t o 4 . 6 p c t C r h a v e b e e n i n v e s t i g a t e d s y s t e m a t i c a l l y in r e l a t i o n t o t e m p e r a t u r e a n d s t r a i n r a t e .3 S u c h s t u d i e s h a v e not b e e n undertaken with a l l o y s containing h i g h e r a m o u n t s of chromium, although the r o o m temperature mechanical p r o p e r t i e s of p o l y c r y s t a l l i n e a l l o y s c o n t a i n i n g up t o 30 p c t C r h a v e b e e n r e p o r t e d . 4 T h e u l t i m a t e t e n s i l e s t r e n g t h a n d d u c t i l i t y of a l l o y s c o n t a i n i n g 20 t o 33 p c t C r 5'8 h a v e b e e n of s o m e i n t e r e s t i n t h e p a s t . I n t h e p r e s e n t s t u d y s i n g l e c r y s t a l s of n i c k e l c o n t a i n i n g up t o 21.5 a t . p c t C r h a v e b e e n d e f o r m e d i n t e n s i o n o v e r t h e t e m p e r a t u r e r a n g e f r o m 78° t o 6 2 3 ° K . T h e work hardening characteristics are reported and t h e CRSS i s a n a l y z e d i n t h e l i g h t of e x i s t i n g s o l u t i o n hardening theories. T h e temperature and s t r a i n rate d e p e n d e n c e of t h e s t r e s s a t t h e o n s e t of d y n a m i c r e c o v e r y h a v e been used t o calculate t h e stacking fault e n e r g y of n i c k e l a s a f u n c t i o n of c h r o m i u m c o n t e n t . PROCEDURE N i c k e l of 9 9 . 9 8 p c t p u r i t y a n d c h r o m i u m c o n t a i n i n g l e s s t h a n 0.01 p c t t o t a l i m p u r i t i e s w e r e u s e d i n t h e p r e s e n t i n v e s t i g a t i o n . S u i t a b l e p r o p o r t i o n s of n i c k e l a n d c h r o m i u m w e r e i n d u c t i o n m e l t e d in a m a g n e s i a c r u c i b l e u n d e r a partially evacuated h e l i u m a t m o s phere. T h e melt w a s allowed t o solidify u n d e r d i r e c tional cooling, thus avoiding pipe formation. T h e c a s t i n g , 10 c m l o n g by 1.9 c m i n d i a m e t e r , w a s h o m o g e n i z e d in a v a c u u m - s e a l e d q u a r t z tube at 1 1 5 0 ° C f o r 24 h r a n d s u b s e q u e n t l y c o l d s w a g e d d o w n t o 4 ~ m m A. AKHTAR and E. TEGHTSOONIAN are Visiting Assistant Professor and Professor, respectively,Department o f Metallurgy, University of British
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