The production and utility of recovered dislocation substructures

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s t r e n g t h of a m e t a l whose g r a i n s contain s u b g r a i n s is g r e a t e r at both a m b i e n t and e l e v a t e d t e m p e r a t u r e s than one with r e c r y s t a l l i z e d g r a i n s of t h e s a m e s i z e . T h e r e c o v e r e d s u b s t r u c t u r e is u s u a l l y w e a k e r , but m o r e d u c t i l e , m o r e c o r r o s i o n r e s i s t a n t and m o r e s t a b l e for high t e m p e r a t u r e s e r v i c e than a d i s l o c a t i o n s u b s t r u c t u r e f o r m e d by d e f o r m a t i o n at o r below a m b i e n t t e m p e r a t u r e s . At high t e m p e r a tures, substructure strengthened material is subject to g r a d u a l s o f t e n i n g by r e c o v e r y o r to c a t a s t r o p i c s o f t e n i n g by r e c r y s t a l l i z a t i o n . Without b e i n g e x h a u s t i v e , the t e c h n o l o g i e s e x a m i n e d i n c l u d e cold w o r k i n g with r e c o v e r y , *,2 fatigue 2,a c r e e p , %4-7 and hot w o r k i n g , 1,7-a4 which involve e i t h e r d y n a m i c r e c o v e r y with c o n c u r r e n t s t r e s s and s t r a i n o r s t a t i c r e c o v e r y without t h e m . A s e x c e l l e n t r e v i e w s ~-~4 e x i s t of the above p r o c e s s e s , the o b j e c t i v e of t h i s p a p e r i s to c o m p a r e t h e i r r e l a t i v e c a p a b i l i t i e s and l i m i t a t i o n s of c r e a t i o n and u t i l i z a t i o n . P r o duction c o n s t r a i n t s r e f e r not only to t h o s e a s s o c i a t e d with i n t e r n a l m e c h a n i s m s but a l s o to p r a c t i c a l p r o c e s s i n g in r e l a t i o n to s h a p e and to p r o p e r t y u n i f o r m i t y . The p r o c e s s e s and m e c h a n i s m s under c o n s i d e r a t i o n have m a n y r e m a r k a b l e s i m i l a r i t i e s in b e h a v i o r while m a i n t a i n i n g s i g n i f i c a n t d i f f e r e n c e s . With i n c r e a s i n g s t r a i n , in e v e r y o n e of t h e m (except r e c o v e r y ) the d i s l o c a t i o n s m u l t i p l y and t a n g l e with the r e s u l t that a c e l l u l a r s u b s t r u c t u r e g r a d u a l l y d e v e l o p s which s a t u r a t e s with r e s p e c t to d i m e n s i o n s . The flow s t r e s s is u s u a l l y p r o p o r t i o n a l to the s q u a r e r o o t of the d i s l o c a t i o n d e n s i t y r e g a r d l e s s of the d e g r e e of c e l l u l a r i t y of the s u b s t r u c t u r e . F u r t h e r m o r e , the s u b g r a i n s b e c o m e l a r g e r with l o w e r i n t e r i o r d i s l o c a t i o n d e n s i t i e s and m o r e o r d e r l y and open b o u n d a r i e s a s any of the following p a r a m e t e r s (as a p p l i c a b l e and H. J. McQUEEN is Professor, Department of Mechanical Engineering, Concordia University, Montreal, Canada H3G i M8. This paper is based on a presentation made at a symposium on "Mechanical-Thermal Processing and Dislocation Substructure Strengthening," held at the Annual Meeting in Las Vegas, Nevada, on

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