Pseudoelasticity and the strain-memory effect in Cu-Zn-Sn alloys
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I N a r e c e n t p a p e r , Pops 1 has shown that c o a r s e g r a i n e d s p e c i m e n s of fl C u - Z n - S n and C u - Z n - S i can have high d e g r e e s of p s e u d o e l a s t i c i t y . In t h e s e a l l o y s the high t e m p e r a t u r e /3 p h a s e is r e t a i n e d on quenching with a m a r t e n s i t e t r a n s f o r m a t i o n o c c u r r i n g j u s t below r o o m t e m p e r a t u r e . On s t r e s s i n g at r o o m t e m p e r a t u r e , the m a r t e n s i t e b e c o m e s t h e r m o d y n a m i c a l l y s t a b l e and g i v e s l a r g e e l o n g a t i o n s to the s p e c i m e n . On r e m o v a l of the s t r e s s the m a r t e n s i t e d i s a p p e a r s and the s p e c i m e n r e g a i n s i t s o r i g i n a l length, thus giving p s e u d o e l a s t i c b e h a v i o r . S i m i l a r p s e u d o e l a s t i c effects have been r e ported in Cu-AI-Ni,2'3 Au-Cd, 4 In-Tl,5 and Ag-Cd. 6 The strain-memory effect has not been specifically reported in the Cu-Zn-Sn system, but has been found in several analogous alloys, such as Au-Cd, 7 In-Tl,8 Ti-Ni,9 Ti-Nb,'~ Cu-AI-Ni,3'n and Cu-Zn.12 In this effect, an alloy is deformed below M s and shows complete recovery on heating to between A s and Af. There is obviously a very close interrelationshipbetween pseudoelastieity and the strain-memory effect and the purpose of this paper will be to discuss this in Cu-Zn-Sn alloys. The observations of Pops I will be extended to cover single crystals, with polycrystalline observations being discussed where they differ from single crystal ones.
EXPERIMENTAL Alloys were melted in evacuated quartz tubes using high purity copper (99.98 pct), zinc (99.999 pct), and tin (99.99 pct) and homogenized by annealing at 810~ for 24 hr. Polycrystalline specimens were produced by hot rollJ. D. EISENWASSERis Graduate Student, Department of Metallurgy, University of British Columbia, Vancouver, Canada. L. C. BROWN, currently on leave from the Department of Metallurgy, University of Melbourne, Victoria, Australia, is Associate Professor, Department of Metallurgy, University of British Columbia. Manuscript submitted October 18, 1971. METALLURGICALTRANSACTIONS
ing at 810~ to a t h i c k n e s s of 0.045 in., and then cold r o l l i n g to 0.040 in. Single c r y s t a l s w e r e grown by the s t a n d a r d B r i d g m a n method. The p r e v i o u s l y cast b i l l e t s w e r e r e s e a l e d in q u a r t z tube and solidified at a r a t e of 5 cm p e r h r f r o m a point to give a c r y s t a l of u n c o n t r o l l e d o r i e n t a t i o n but with a t e n d e n c y to be m o d e r a t e l y close to (110). Slices 0.040 in. thick w e r e cut f r o m the b i l l e t s by s p a r k machining. T e n s i l e s p e c i m e n s w e r e p r o d u c e d f r o m the s i n g l e and p o l y c r y s t a l l i n e s t r i p by s p a r k m a c h i n i n g . They w e r e solution t r e a t e d at 810~ for 1 m i n and then quenched into 10 pct c a u s t i c soda solution to r e t a i n the fl p h a s e . T
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