Dislocation transport and hydrogen embrittlement
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T HE potential role of hydrogen t r a n s p o r t by d i s l o c a tions in hydrogen e m b r i t t l e m e n t p r o c e s s e s has been d i s c u s s e d by numerous i n v e s t i g a t o r s since the concept was f i r s t p r o p o s e d in the e a r l y 1950's. ',2 The f i r s t e x p e r i m e n t a l evidence for such t r a n s p o r t was r e p o r t e d in the late 1950's when deformation enhanced hydrogen outgassing was o b s e r v e d in mild s t e e l s . 3 However, the concept did not r e c e i v e widespread attention until the e a r l y 1970's when d i r e c t evidence for d i s l o c a t i o n a s s i s t e d hydrogen t r a n s p o r t was observed.% 5 The use of the r a d i o a c t i v e hydrogen isotope, t r i t i u m , to study t r a n s p o r t kinetics g r e a t l y enhanced the e x p e r i m e n t a l a c c u r a c y of hydrogen r e l e a s e m e a s u r e m e n t s and p e r mitted the d e m o n s t r a t i o n of deformation enhanced hydrogen a b s o r p t i o n . 5 Subsequent to the t r i t i u m t r a n s port and r e l e a s e m e a s u r e m e n t s , i n v e s t i g a t o r s a s s o ciated dislocation t r a n s p o r t as c r i t i c a l to hydrogen embrittlement processes. The development of high l o c a l i z e d hydrogen p r e s s u r e s , 6 c o r r e l a t i o n s between hydrogen c o m p a t i b i l i t y and stacking fault energy, 7 the effect of a d i s p e r s e d phase on hydrogen compatibility,s c o r r e l a t i o n s b e tween lattice m i s f i t p a r a m e t e r and hydrogen p e r f o r mance of p r e c i p i t a t i o n strengthened s t a i n l e s s s t e e l s , 9 the sweeping of hydrogen to g r a i n boundaries, ~~ e n v i r o n m e n t a l effects on fatigue c r a c k growth, ~ and hydrogen p a r t i c i p a t i o n in ductile rupture p r o c e s s e s 12 have been r a t i o n a l i z e d a n d / o r d e s c r i b e d in t e r m s of hydrogen t r a n s p o r t by d i s l o c a t i o n s . These r a t i o n a l i z a tions and numerous s i m i l a r r e p o r t s a r e e x p e r i m e n t a l l y based, t y p i c a l l y qualitative and g e n e r a l l y r e q u i r e the a s s u m p t i o n that localized high concentrations of hydrogen a r e developed. A quantitative model for the l o c a l ization of hydrogen by dislocation t r a n s p o r t lz p r e d i c t s e x t r e m e l y s m a l l v~tues for kinetic s u p e r s a t u r a t i o n when a balance between hydrogen a r r i v a l and d e p a r t u r e r a t e s is obtained. This calculation leads to the conclusion that hydrogen e m b r i t t l e m e n t cannot be explained by kinetic s u p e r s a t u r a t i o n a r g u m e n t s . The significance of this conclusion can be minimized ANTON J. WEST is Member of Technical Staff, Sandia Laboratories, Livermore, CA 94550. MaclNTYRE R. LOUTHAN,JR. is Professor, MaterialsEngineering Department, VirginiaPolytechnic Institute, Blacksburg, VA 24061. Manuscript submitted November 20, 1978. METALLURGICAL TRANSACTIONS A
by showing that when the binding e n e r g y of hydro
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