Migration kinetics of 37 deg coincidence boundaries in copper bicrystals
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In conclusion, it has been o b s e r v e d that in the t e m p e r a t u r e range 360 to 580~ 37 deg coincidence bounda r i e s have higher m o b i l i t i e s than r a n d o m high-angle boundaries in 99.999 wt pct c o p p e r . The higher m o b i l i t i e s obtain despite the fact that the activation e n e r g y of m i g r a t i o n for the coincidence b o u n d a r i e s is about 12 k c a l / m o l e l a r g e r than that obtained for random b o u n d a r i e s . F u r t h e r studies a r e needed to r e s o l v e the o r i g i n s of the orientation dependence of mobility and to a s c e r t a i n if m i g r a t i o n of coincidence boundaries is c h a r a c t e r i z e d by different values of Q in different r e g i o n s of t e m p e r a t u r e . Financial support of the p r e s e n t r e s e a r c h by the National Science Foundation is g r a t e f u l l y acknowledged.
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A Dislocation Cascade Mechanism in Superplasticity P. CHAUDHARI The r a t e controlling m e c h a n i s m in s u p e r p l a s t i c d e f o r m a t i o n is g e n e r a l l y a c c e p t e d to be diffusion cont r o l l e d . Grain boundary sliding is c o n s i d e r e d to be significant and an accommodation p r o c e s s is then r e quired to maintain continuity of m a t e r i a l . 1 There a r e two d i s t i n c t ways in which accommodation can proceed. In one diffusion c r e e p o c c u r s at t r i p l e - p o i n t s and in the other d i s l o c a t i o n s a r e g e n e r a t e d at t r i p l e - p o i n t s and these d i s l o c a t i o n s move through the grain and p i l e - u p at a boundary.* Climb at the head of the p i l e - u p leads *Although we have emphasized triple-points here, the same argument holds for ledges in a grain boundary. One of the differences between ledges and triple points is that ledges are removed with deformation until triple-points are left. The strain or history dependent part of superplastic deformation is, we believe, associated with the gradual removal of ledges until smooth grain boundaries (or interfaces) are obtained.
to continuous p l a s t i c flow. The p u r p o s e of this note is to show that t h e r e is an i n c r e a s e in s t r a i n - r a t e
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