Exceptional ductility in the superplastic Pb-62 Pct Sn eutectic
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F o u r t e n s i l e s p e c i m e n s , e a c h h a v i n g a gage s e c t i o n 0.635 c m in length and 0.508 c m wide, w e r e cut f r o m the s h e e t p a r a l l e l to the r o l l i n g d i r e c t i o n , and a n n e a l e d f o r 1 h a t 433 K to give an a v e r a g e s p a t i a l g r a i n d i a m e t e r (equal to 1.74 • m e a n l i n e a r i n t e r c e p t ) of 6.9 ~ n . T h e s p e c i m e n s w e r e t e s t e d b y i m m e r s i n g in an e l e c t r i c a l l y - h e a t e d s i l i c o n e o i l bath, s t i r r e d with b u b b l i n g a r g o n , in which the t e m p e r a t u r e was m a i n t a i n e d cons t a n t at 413 • 1 K. A f t e r holding at t e m p e r a t u r e f o r 25 rain, the s p e c i m e n s w e r e p u l l e d in an I n s t r o n t e s t ing m a c h i n e at a c o n s t a n t r a t e of c r o s s - h e a d d i s p l a c e m e n t which w a s e q u i v a l e n t to an i n i t i a l s t r a i n r a t e of 1.33 x 10 -4 s "1. T h i s s t r a i n r a t e was s e l e c t e d b e c a u s e e a r l i e r w o r k i n d i c a t e d that i t was within the r e g i o n f o r which m = 0.61.8 MOHAMED M. I. AHMED and TERENCE G. LANGDON are Graduate Research Assistant and Professor, respectively, Department of Materials Science, University of Southern California, Los Angeles, CA 90007. Manuscript submitted April 18, 1977. 1832-VOLUME 8A, NOVEMBER 1977
Some s c a t t e r was e v i d e n t in the o v e r a l l t e n s i l e b e h a v i o r of t h e s e f o u r s p e c i m e n s . T h r e e of the s p e c i m e n s f a i l e d a t e l o n g a t i o n s of 3400 pct, 3800 pct, and 4000 pct, r e s p e c t i v e l y , w h e r e the e l o n g a t i o n is d e fined a s A L / L o p c t w h e r e zXL i s the t o t a l i n c r e a s e in length at the point of f a i l u r e and L o is the i n i t i a l s p e c i m e n gage length. F o r the f o u r t h s p e c i m e n , the t e s t was t e r m i n a t e d p r i o r to f r a c t u r e at an e l o n g a t i o n of 4850 pct, when it b e c a m e a p p a r e n t that f u r t h e r d e f o r m a t i o n would b r i n g the u p p e r p o r t i o n of the s p e c i m e n g r i p above the s u r f a c e of the s i l i c o n e oil. The l a t t e r s p e c i m e n , shown at B in F i g . 1, p u l l e d down to a v e r y thin w i r e , with no e v i d e n c e of any m a c r o s c o p i c n e c k i n g within the gage s e c t i o n . F o r c o m p a r i s o n , an u n t e s t e d s p e c i m e n i s shown at A in F i g . 1. T h e e x c e p t i o n a l d u c t i l i t i e s o b s e r v e d in t h e s e four s p e c i m e n s , with a m a x i m u m in one c a s e of 4850 p c t without f a i l u r e , r e p r e s e n t the h i g h e s t e l o n g a t i o n s r e p o r t e d to d a t e in any s u p e r p l a s t i c m a t e r i a l . It i s t h e r e f o r e a p p r o p r i a t e to c o m p a r e t h e s e e x p e r i m e n t a l r e s u l t s with the p r e d i c t i o n s of two r e l a t i o n s h i p s which w e r e s p e c i f i c a l l y d e v e l o p e d f o r
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