Transformational elasticity in a polycrystalline Cu-Zn-Sn alloy
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P R E V I O U S work has shown that s i n g l e c r y s t a l s of CuZn-Sn can be quenched to low t e m p e r a t u r e s to r e t a i n the high t e m p e r a t u r e /3-phase. The /3-phase,* on cool*Thebcc 13-phasein Cu-Znalloysis knownto orderveryrapidlyto the cesium chloridestructureon cooling below454~ (2). The effectof Sn on the ordering kineticshas not beenestablished. ing below r o o m t e m p e r a t u r e , t r a n s f o r m s to an o r t h o rhombic product by a martensite reaction. 1 A m a r t e n site product can also be f o r m e d b y the application of s t r e s s at t e m p e r a t u r e s above MS .2 The s t r e s s - i n d u c e d m a r t e n s i t e (SIM) shows only a s m a l l n u m b e r of the p o s sible m a r t e n s i t e v a r i a n t s . Only those v a r i a n t s will f o r m for which the applied load p r o d u c e s the s t r e s s n e c e s s a r y to i n i t i a t e the t r a n s f o r m a t i o n . If the SIM f o r m s at t e m p e r a t u r e s > Af, i . e . , when M d > Af, the m a r t e n s i t e p l a t e s will d i s a p p e a r on r e l e a s e of the applied s t r e s s , giving r i s e to the p h e n o m e n o n c a l l e d s u p e r e l a s t i c i t y (SE), t r a n s f o r m a t i o n a l e l a s t i c i t y (TE) or pseudo e l a s t i c i t y ( P S E ) J '4,s'e'7 In this case the m a r t e n s i t e is e l a s t i c a l l y a c c o m m o d a t e d in the s u r r o u n d i n g m a t r i x . When the applied s t r e s s exceeds the flow s t r e s s of the p a r e n t phase, p l a s t i c d e f o r m a t i o n m a y r e s u l t in the f o r m a t i o n of n o n - r e v e r s i b l e , s t r a i n - i n d u c e d m a r t e n siteJ The morphology and s t r u c t u r e of m e c h a n i c a l l y i n duced m a r t e n s i t e in Cu- Zn b a s e alloys has b e e n r e p o r t e d b y s e v e r a l a u t h o r s . 9'1~ Applications of the W. L. R. T h e o r y '2 gave a m a r t e n s i t e habit plane in m o d e r a t e a g r e e m e n t with that e x p e r i m e n t a l l y o b served.V, 13 P r e v i o u s work has e s t a b l i s h e d the shape of the s t r e s s - s t r a i n c u r v e s for s i n g l e c r y s t a l C u - Z n - S n s p e c i m e n s at t e m p e r a t u r e s above Af. 3'7 L a r g e r e v e r s i b l e s t r a i n s (> 2.5 pct) w e r e r e a l i z e d in s p e c i m e n s in which the t e n s i l e axis was close to the [110] or the [111] d i r e c t i o n . The c r y s t a l s t r a n s f o r m e d with s i n g l e m a r t e n s i t e plate v a r i a n t s a p p e a r i n g . M i n i m a l t r a n s -
I. DVORAKis with the Engineering Department, Lister Bolt and Chain, 177 Savage Rd., Richmond, B. C. E. B. HAWBOLTis Assistant Professor, Metallurgy Department, University of British Columbia, Vancouver, B. C. Manuscript submitted December 5, 1973. METALLURGICALTRANSACTIONSA
f o r m a t i o n a l e l a s t i c i t y was r e a l i z e d when the t e n s i l e axis was p a r a l l e l to the [001] d i r e c t i o n in the c r y s t a l . 9 The e l a s t i c a n i
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