• PDF / 693,472 Bytes
• 7 Pages / 613 x 788.28 pts Page_size
• 88 Downloads / 255 Views

DOWNLOAD

REPORT

---

1. INTRODUCTION W HE p l a s t i c d e f o r m a t i o n of cubic and hexagonal m e t a l s has b e e n the s u b j e c t of i n t e n s i v e r e s e a r c h for m o r e than half a c e n t u r y and much is known about t h e i r d e f o r m a t i o n b e h a v i o r and the effects of d e f o r m a t i o n on t h e i r p r o p e r t i e s . By c o n t r a s t , knowledge of the m e c h a n i c a l b e h a v i o r of m e t a l s with c r y s t a l s t r u c t u r e s of lower s y m m e t r y is quite l i m i t e d . The published i n f o r m a t i o n on the d e f o r m a t i o n of b i s muth, which has a r h o m b o h e d r a l s t r u c t u r e , r e l a t e s p r e d o m i n a n t l y to single c r y s t a l s . The l i t e r a t u r e cont a i n s r e p o r t s on i n v e s t i g a t i o n s of s i n g l e c r y s t a l s of b i s m u t h d e f o r m e d by t o r s i o n 1 and in t e n s i o n , 2 the a n i s o t r o p y of its m i c r o h a r d n e s s 3 and twinning as one of its d e f o r m a t i o n m e c h a n i s m s . 4,~ The t e m p e r a t u r e dependence of the c r i t i c a l s h e a r s t r e s s 6 and h a r d n e s s 7 have also b e e n r e p o r t e d . No m e a s u r e m e n t s of the s t o r e d e n e r g y of cold work have b e e n published for b i s m u t h or other m e t a l s of low c r y s t a l s y m m e t r y . 8 In the lattice of b i s m u t h , the planes of m a x i m u m a t o m i c d e n s i t y (1i0), (01i) and (i01) do not contain the lines of the c l o s e s t a t o m i c s p a c i n g i l l 0 ] , [01i] and [101]; all t h r e e of these d i r e c t i o n s lie in the (111) plane which is p e r p e n d i c u l a r to the t r i g o n a l axis of s y m m e t r y of the lattice .9 It has b e e n stated that in b i s m u t h single c r y s t a l s d e f o r m e d in t e n s i o n , the welldefined p s e u d o o c t a h e d r a l (111) plane is the o p e r a t i n g slip plane. 2 T h i s plane should be d i s t i n g u i s h e d f r o m the t h r e e l e s s w e l l - d e f i n e d (111) p l a n e s which a r e at an angle of 71 deg 37.5 m i n f r o m the (111) slip plane. We r e p o r t h e r e an i n v e s t i g a t i o n of the d e f o r m a t i o n b e h a v i o r in c o m p r e s s i o n and m e a s u r e m e n t s of the s t o r e d e n e r g y of cold work of p o l y c r y s t a l l i n e b i s m u t h . We d e t e r m i n e d the s t r a i n r a t e s e n s i t i v i t y of the flow s t r e s s by s t r a i n r a t e change e x p e r i m e n t s and obt a i n e d the t e m p e r a t u r e s e n s i t i v i t y of the flow s t r e s s GAURI C. DAS is Research Engineer, Leybold-HeraeusVacuum Systems Inc., Enfield, CT 06082 and MICHAELB. BEVER is Professor of Materials Science and Engineering,Emeritus, Senior Lecturer, Department of Materials Science and Engineering,Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted January 4, 1978. METALLURGICALTRANSACTIONSA

f r o m i s o t h e r m a l t e s t data for s e v e r a l t e m p e r a t u r e s . The