Radiation-induced solute segregation and precipitation in alloys
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B I N D I N G b e t w e e n s o l u t e s and r a d i a t i o n - i n d u c e d point defects can lead to the coupling of solute fluxes to defect c u r r e n t s in alloys u n d e r i r r a d i a t i o n . The solute fluxes, in t u r n , cause local c o m p o s i t i o n a l changes in a l l o y s . Okamoto and W i e d e r s i c h 1 have shown that the u n d e r s i z e d s o l u t e s Si and Ni in an Si-doped F e - 1 8 C r 8Ni alloy s e g r e g a t e to defect sinks, w h e r e a s Cr, an o v e r s i z e d atom, is depleted at s i n k s d u r i n g i r r a d i a tion. S i m i l a r effects have also b e e n o b s e r v e d m o r e r e c e n t l y in other F e - C r - N i b a s e alloys by J o h n s t o n and c o - w o r k e r s 2 and by Kenik." In addition, s t u d i e s on r a d i a t i o n - i n d u c e d s e g r e g a t i o n in N i - b a s e b i n a r y alloys 4-6 have shown that u n d e r s i z e d Be and Si segregate to s i n k s , w h e r e a s the o v e r s i z e d A1 moves away f r o m s i n k s . The u n d e r s i z e d and o v e r s i z e d s o l u t e s a r e defined in the p r e s e n t context as solutes that cause n e g a t i v e and positive changes, r e s p e c t i v e l y , in the lattice p a r a m e t e r of the host m e t a l . F r e q u e n t l y , the r a d i a t i o n - i n d u c e d , n o n e q u i l i b r i u m s e g r e g a t i o n leads to p r e c i p i t a t i o n of a second phase or, p o s s i b l y , p l a t i n g of a p r e c i p i t a t e l a y e r on the s i n k s u r f a c e when the s o l u b i l i t y l i m i t has b e e n s u r p a s s e d . T h i s r a d i a t i o n - i n d u c e d p r e c i p i t a t i o n p h e n o m e n o n is thought to be i m p o r t a n t r e l a t i v e to void swelling b e c a u s e the f o r m a t i o n of p r e c i p i t a t e s leads to depletion of the m a t r i x of s o l u t e s , which can be e s p e c i a l l y s e v e r e at t e m p e r a t u r e s below the p e a k - s w e l l i n g t e m p e r a t u r e . N. Q. LAM,P. R. OKAMOTO,H. WIEDERSICH,and A. TAYLORare Scientists in the MaterialsScienceDivisionof ArgonneNationalLaboratory. Thispaperis basedon a presentationmadeat a symposiumon "RadiationInducedAtomicRearrangementsin Orderingand ClusteringAlloys"held at the annualmeetingof the AIME,Atlanta,Georgia,March7 to 8, 1977,underthe sponsorshipof the PhysicalMetallurgyand NuclearMetallurgyCommitteesof The MetallurgicalSocietyof AIME. METALLURGICALTRANSACTIONSA
The depletion d e c r e a s e s the s w e l l i n g r e s i s t a n c e of an alloy that can be induced by m i n o r solute additions .~,8 R a d i a t i o n - i n d u c e d solute s e g r e g a t i o n to e x t e r n a l s u r f a c e s and i n t e r n a l sinks has been i n v e s t i g a t e d t h e o r e t i c a l l y by J o h n s o n and Lain 9-12 u s i n g a kinetic model which i n c l u d e s the effects of vacancy and i n t e r s t i t i a l diffusional e n c o u n t e r s with s o l u t e s , as well as the f o r m a t i o n , the d i s s o c i a t i o n , and the m i g r a t i o
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