Stress-induced pseudoelasticity in ternary Cu-Zn based beta prime phase alloys
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is c h a r a c t e r i s t i c of the bcc #3' p h a s e s that they t r a n s f o r m m a r t e n s i t i c a l l y during cooling and that this t r a n s f o r m a t i o n is v e r y s e n s i t i v e to s t r a i n . In a few s y s t e m s , such as C u - Z n , 1 the m a r t e n s i t e phase may f o r m " t h e r m o e l a s t i c a l l y " , during which p r o c e s s the m a r t e n s i t e p l a t e s g r o w as the t e m p e r a t u r e i s l o w e r e d and s h r i n k upon h e a t i n g , with l i t t l e o r no t e m p e r a t u r e h y s t e r e s i s . It is a l s o c o m m o n f o r a s i m i l a r f o r m of m a r t e n s i t e to grow d u r i n g a p p l i c a t i o n of s t r e s s and to s h r i n k or d i s a p p e a r when the load is r e m o v e d . The f o r m a t i o n u n d er s t r e s s of a r e v e r s i b l e " e l a s t i c " m a r t e n s i t e m ay r e s u l t in r u b b e r - l i k e p r o p e r t i e s . T h i s has b e e n r e p o r t e d for In-T1, 2 A u - C d , 3 and Cu-A1Ni 4 a l l o y s . The t e r m " s u p e r - e l a s t i c i t y " was u s e d by R a c h i n g e r 4 in 1960 to d e s c r i b e the l a r g e e l a s t i c s t r a i n s (~4 pct) which o c c u r r e d at r o o m t e m p e r a t u r e during the s t r e s s i n g of single c r y s t a l s of C u - 14 .5 A1-3 Ni a l l o y s . S u p e r e l a s t i c b e h a v i o r has a l s o b e e n o b s e r v e d in c o a r s e g r a i n e d p o l y c r y s t a l l i n e Cu-A1-Ni a l l o y s , s Much at t e n ti o n h a s been f o c u s s e d r e c e n t l y on the N i T i a l l o y s 6 (the Nitinols) which show a v e r y unusual m e c h a n i c a l " s h a p e - m e m o r y " e f f e c t a s a r e sult of a m a r t e n s i t i c t r a n s f o r m a t i o n . T h e r m o e l a s t i c m a r t e n s i t e was studied in p r e v i o u s i n v e s t i g a t i o n s 7'8 of t e r n a r y a l l o y s b a s e d upon the C u - Z n / 3 ' b r a s s phase ( C u - Z n - N i , C u - Z n - A g , C u - Z n Au, C u - Z n - C d , C u - Z n - I n , C u - Z n - G a , C u - Z n - S i , C u - Z n - G e , C u - Z n - S n , and C u - Z n - S b ) . The data indic a t e d that by a suitable c h o i c e of c o m p o s i t i o n , t h ese a l l o y s might show r u b b e r - l i k e b e h a v i o r u n d e r s t r e s s n e a r r o o m t e m p e r a t u r e . On the b a s i s of p r e l i m i n a r y e x p e r i m e n t s , 9 the s y s t e m s C u - Z n - S i and C u - Z n - S n w e r e s e l e c t e d for f u r t h e r d e t a i l e d s t u d i e s . T h e object of this r e s e a r c h was to d e t e r m i n e the extent of e l a s t i c i t y o c c u r r i n g a s a r e s u l t of the e l a s t i c m a r t e n s i t e t r a n s f o r m a t i o n . The r o l e of a p p l i e d s t r e s s , t r a n s f o r m a t i o n t e m p e r a t u r e , and t e s t t e m p e r a t u r e was a l s o examined.
l e c t e d in the r an g e b e t w e e n r o o m t e m p e r a t u r e and approximately -50~ Six C u - Z n - S i and C u - Z n - S n a l l o y s , eac
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