Analysis of liquid metal embrittlement from a bond energy viewpoint
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AND
N. S. STOLOFF
A b s o r p t i o n induced e m b r i t t l e m e n t of solid m e t a l s by c e r t a i n liquid m e t a l s is a n a l y z e d through an E n g e l - B r e w e r c a l c u l a t i o n of the s o l i d - l i q u i d i n t e r a c t i o n e n e r g y , and the effect of the l a t t e r in r e d u c i n g f r a c t u r e s u r f a c e e n e r g y . The r e d u c t i o n in f r a c t u r e s u r f a c e e n e r g y is e s t i m a t e d b y c o m p a r i s o n of the e l e c t r o n i c c o n t r i b u t i o n to the s o l i d - l i q u i d i n t e r a c t i o n e n e r g y with s o l i d - s o l i d bond e n e r g y for s o m e 40 l i q u i d - s o l i d couples. R e g u l a r s o l u t i o n t h e o r y is used to e s t i m a t e m u t u a l s o l u b i l i t y as the r e l a t i v e d i f f e r e n c e in p a r a m e t e r v a l u e s . E m b r i t t l e m e n t can be p r e d i c t e d by u s i n g r e d u c t i o n in f r a c t u r e s u r f a c e e n e r g y and s o l u b i l ity p a r a m e t e r d i f f e r e n c e as c r i t i c a l v a r i a b l e s . The effect of solute additions to the liquid on the d e g r e e of e m b r i t t l e m e n t is i n t e r p r e t e d v i a the s a m e two v a r i a b l e s ; the p r i n c i p a l effect of s o l u t e s is to modify s o l u b i l i t y r e l a t i o n s h i p s at the s o l i d - l i q u i d i n t e r f a c e . F i n a l l y , s i n c e solute additions to the solid m a y affect the yield s t r e s s , Petch slope and f r a c t u r e s u r f a c e e n e r g y in a i r , the C o t t r e l l - P e t c h f r a c t u r e r e l a t i o n is shown to be a n e c e s s a r y f r a m e w o r k for i n t e r p r e t i n g the effects of such additions on e m b r i t t l e m e n t p h e n o m e n a . T H E sudden o n s e t of b r i t t l e f a i l u r e of a solid m e t a l in the p r e s e n c e of a liquid m e t a l where s o m e f o r m of ductile f a i l u r e would o t h e r w i s e have b e e n o b s e r v e d was f i r s t noted s o m e s i x t y y e a r s ago and has b e e n the s u b j e c t of s e v e r a l r e c e n t r e v i e w s . ~-3 It is g e n e r a l l y a g r e e d that the m e c h a n i s m of liquid m e t a l e m b r i t t l e m e n t (LME) is the r e d u c t i o n b y a d s o r p t i o n of the e n e r g y needed to b r e a k atomic bonds at the tip of a c r a c k in the solid (effective f r a c t u r e s u r f a c e e n e r g y - F S E ) such that b r i t t l e f a i l u r e is induced. 4'6 Additional c o n ditions a r e indicated to be that the solid m u s t not be s i g n i f i c a n t l y soluble in the liquid and that the liquid m u s t wet the solid, l's V a r i o u s t h e o r e t i c a l a p p r o a c h e s have b e e n made to the p r o b l e m of LME, but, in g e n e r a l , q u a n t i t a t i v e e s t i m a t e s of r e d u c t i o n in FSE in the p r e s e n c e of liquid m e t a l and s y s t e m a t i c p r e d i c t i o n of specific e m b r i t t l e m e n t couples have not b e e n p o s s i b l e . Chaevski
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