Force relations applicable to dislocation-forest intersections
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m a c r o s c o p i c t h e o r i e s o f l i n e a r , s t a g e If, w o r k h a r d e n i n g , 1-6 t h e r e i s g e n e r a l a g r e e m e n t that i n t e r s e c tion of gli-te dislocations with forest dislocation t h r e a d i n g the glide plane is a prominent mechanism in accounting for the temperature dependent portion of the flow stress. Other mechanisms, such as the drag of sessile jogs, have also been considered.6 There is not as good agreement on whether the forest intersection contributes to the temperature independent portion of the flow stress, but this view has been advanced by B a s i n s k i .4' s T h e r e a r e a v a r i e t y o f w a y s in w h i c h t h e f o r e s t i n tersection p r o c e s s can influence the flow s t r e s s . Some o f t h e s e a r e not c o n s i d e r e d i n d e t a i l h e r e but a r e m e n t i o n e d f o r c o m p l e t e n e s s . O n e o f t h e s e m o d e l s is t h e f o r m a t i o n o f a t t r a c t i v e j u n c t i o n s , e i t h e r in u n e x t e n d e d dislocations7, 8 or in extendeddislocations.9' 1o The junction models involve essentially line tension forces because of line length changes and dislocation combinations. These junctions are considered to provide such strong barriers that they contribute only to the temperature independent flow stress. A similar model for a repulsive junction was treated by Mitra et al.11 They developed a linear force-distance curve for the intersection process based on line tension forces associated with bow out of the forest dislocations. Finally, there is the possibility of local crossslip or climb under the large local forces near an intersection site ,12 leading to the subsequent dislocation p r o c e s s e s o f m u s h r o o m i n g , 13 h e l i x f o r m a t i o n , 14' is o r d i p o l e f o r m a t i o n , 1~' 1~ a l l o f w h i c h i n t u r n a f f e c t h a r d ening. O f i n t e r e s t i n the p r e s e n t w o r k i s t h e elastic i n t e r action between an unextended g l i d e and forest d i s l o c a t i o n , b o t h r e s t r i c t e d t o b o w out only i n t h e i r g l i d e p l a n e . T h e g e n e r a l v i e w that h a s b e e n a d o p t e d f o r m e r l y f o r t h i s c o n t r i b u t i o n to t h e i n t e r s e c t i o n p r o c e s s r e s e m b l e s that o r i g i n a l l y p r o p o u n d e d by H e i d e n r e i c h a n d S h o c k l e y . 18 That i s , t h e e l a s t i c i n t e r a c t i o n i s e i t h e r c o n s t a n t o r n e g l i g i b l e , a n d the e n e r g y b a r r i e r t o t h e i n t e r s e c t i o n is c o m p r i s e d o f t h e e n e r g y to c r e a t e k i n k s a n d / o r j o g s a n d that t o c o n s t r i c t t h e d i s l o c a t i o n s i f they a r e e x t e n d e d . 18-2° S e v e r a l a u t h o r s h a v e r e c o g n i z e d that t h e a c t u a l c o n f i g u r a t i o n d u r i n g a n i n t e r s e c M. N. S H E T T Y 3nd J. P. H I R T H are Research Fellow and Professor, respectively, Metallurgical Engineering Department,Ohio St
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