Mechanical twinning of Cu-1Wt pct be at room temperature
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low enough that Pb2Au p r e c i p i t a t e s did not form after quenching as was o b s e r v e d with the s a m p l e s of set D. T h i s concept of a changing g r a i n b o u n d a r y s t r u c t u r e is also s u p p o r t e d by the work of G l e i t e r 7 on boundary e n e r g i e s in lead. G l e i t e r found that t h e r e was a d i s continuity in boundary e n e r g y as a function of t e m p e r a t u r e at a p a r t i c u l a r t e m p e r a t u r e . He has a t t r i b u t e d this phenomenon to a change in b o u n d a r y s t r u c t u r e which i s s i m i l a r in n a t u r e to an allotropic phase t r a n s f o r m a t i o n or change in c r y s t a l s t r u c t u r e at a p a r t i c u l a r t e m p e r a t u r e . The a u t h o r s a r e grateful to the National R e s e a r c h Council of Canada and the Defence R e s e a r c h B o a r d of Canada for f i n a n c i a l support. 1. C. J. Simpson,K. T. Aust,and W.C Winegard.to be pubhshedmMet. Trans. 2 C. J. Simpsonand W.C Winegard:Trans. TMS-AIME, 1969,vol.245, pp. 43132 3. P. Gordonand R A. Vandermeer Trans TMS-AIME, 1962,voL 224, pp. 91728
4. J. W.Cahn:ActaMet, 1962,vol. 10, pp. 789-98 5, E. S. Machhn:Trans TMS-AIME, 1962,vol 224,pp. 1153-67. 6. K. Luckeand H P. Stuwe.Recovery and Recrystallization of Metals, pp. 171209, lnterscmnce,NewYork, 1963. 7. H Gleiter HarvardUmverslty,Cambridge,Mass.,privatecommumcatlon,1969.
Mechanical Twinning of Cu-lWt Pct Be at Room Temperature B. C. WONSIEWlCZ, T. C. TISONE, AND G. Y. CHIN
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c o u r s e of e x p e r i m e n t a l i n v e s t i g a t i o n s of the p l a s t i c i t y of copper and c o p p e r - b a s e d single c r y s t a l s , we have detected m e c h a n i c a l t w i n n i n g in aged C u - B e d e f o r m e d at r o o m t e m p e r a t u r e for what we b e l i e v e is the f i r s t t i m e . Single c r y s t a l s were grown from the m e l t , s p a r k m a c h i n e d into 8 m m c u b e s , solution t r e a t e d a t 800~ quenched, and then aged for 2 hr at 340~ C h e m i c a l a n a l y s i s a f t e r heat t r e a t i n g r e v e a l e d the c o m p o s i t i o n to be Cu-1 wt pct B e - 0 . 3 5 wt pct Co. The c r y s t a l s were d e f o r m e d in plane s t r a i n c o m p r e s sion, a c o m p r e s s i o n test in which the l a t e r a l expansion i s l i m i t e d by the confining walls of a channel. 1 S e v e r a l o r i e n t a t i o n s were t e s t e d in a l a r g e r study a i m e d at a s s e s s i n g the validity of the T a y l o r a n a l y s i s . 2 One c r y s t a -l- g, . c o m p r e s s e d along (112) with e x t e n sion l i m i t e d to [ 111], exhibited a s t r e s s s t r a i n curve v e r y d i f f e r e n t f r o m the other c r y s t a l s . At a s t r a i n of about 0.11, a s t r e s s m a x i m u m o c c u r r e d followed by s t r a i n softening. To i n v e s t i g a t e the o r i g i n of this p e c u l i a r b e h a v i o r , a { 111 } b a c k r e f l e c t i o n pole figure was taken u s i n g n i c k e l - f i l t e r e d C u K a r a d i a t i o
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