The substitution of Cu for Ni in NiTi shape memory alloys
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y i e l d s t r e s s is e x p e c t e d in t h e f o r m e r c a s e . T h e o b s e r v e d v a l u e o f t h e y i e l d s t r e s s in t h e s p e c i m e n s w i t h 34.5 a t . p c t A1 a f t e r s l o w c o o l i n g i s b e l o w t h e v a l u e of t h e o t h e r t w o c o m p o s i t i o n s . A l i k e l y e x p l a n a t i o n o f t h i s e f f e c t i s that t h i s c o m p o s i t i o n i s v e r y c l o s e to the stoichiometric composition of the comp o u n d CulTA19. W o o d a n d W e s t b r o o k ~° h a v e o b s e r v e d t h a t a m i n i m u m in t h e f l o w s t r e s s is s h o w n at o r n e a r t h e s t o i c h i o m e t r i c c o m p o s i t i o n of s o m e i n t e r m e t a l l i c compounds. T h i s w o r k w a s p a r t i a l l y s u p p o r t e d by t h e I n t e r n a tional Copper R e s e a r c h Association.
1. M. Snykers, R. Serneels,P. Delavignette, R. Gevers, and S. Amelinckx: Crys. Lattice Defects, 1972, vol. 3 , p . 99. 2. P. Goodman and G. Lehmpfuhl: Acta Crystallogr., 1968, vol. A24, p . 339. 3. G. Torres-Villasefior and S. V. Radcliffe: Appl. Phys. Lett., 1975, vol. 27, p . 172. 4 . A. J. Morton: Phys. Status. Solidi., 1975, vol. 31 (a), p . 661. 5. S. Amelinckx: J. Less-CommonMetals, 1972, vol. 28, p. 325. 6. R. Serneels, M. Snykers, P. Delavignette, R. Gevers,and S. Amelinckx: Phys. Status. Solidi., 1973, vol. 58, p. 277. 7. G. Das and S. V. Radcliffe: J. Jap. Inst. Metals, 1968, vol. 9, p. 334. 8. D. Francois and T. R. Wilshaw: J. Appl. Phys., 1968,vol. 39, p . 4170. 9. S. Amelinckx: Frontiers in Materials Science, p. 67, Marcel Dekker, Inc., New York and Basel, 1976. 10. D. L. Wood and J. H. Westbrook: Trans. TMS-AIME, 1962, vol. 224, p. 1024.
The Substitution of Cu for Ni in NiTi Shape Memory Alloys OLIVIER M E R C I E R AND K E I T H N. MELTON T h e e q u i a t o m i c o r n e a r e q u i a t o m i c N i T i a l l o y is w e l l k n o w n f o r i t s s h a p e m e m o r y e f f e c t 1-4 i n w h i c h deformation near the martensite transformation temp e r a t u r e M s c a n be f u l l y r e c o v e r e d o n h e a t i n g . I t h a s b e e n r e p o r t e d by m a n y w o r k e r s2'5'6 t h a t M s i s v e r y strong~,y d e p e n d e n t o n the a l l o y c o m p o s i t i o n , d e c r e a s i n g t h e t i t a n i u m c o n t e n t l e a d i n g t o a r a p i d l o w e r i n g of M s . T h i s c o m p o s i t i o n d e p e n d e n c e is particularly s t r o n g i n t h e v i c i n i t y of r o o m t e m p e r a t u r e , so t h a t w h e r e m a t e r i a l f o r a p p l i c a t i o n s a b o v e a m b i e n t is r e q u i r e d , c o m p o s i t i o n f l u c t u a t i o n c a n r e s u l t in a n a l l o y w h o s e m e m o r y e f f e c t is b e l o w t e m p e r a t u r e . T h e r e is o n l y l i m i t e d i n f o r m a t i o n on t h e i n f l u e n c e of t e r n a r y a d d i t i o n s 4'7'8 a n d i n m o s t c a s e s t h e s e l e a d t o a d e c r e a s e in M s . C u r r e n t l y t h e m a i n use o f a l l o y i n g e l e m e n t s in N i T i i
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