The effect of semicoherent precipitation on void swelling in Al-Cu alloys
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IT has b e e n shown e x p e r i m e n t a l l y that
a high d e n s i t y of s m a l l p r e c i p i t a t e s , or continuous s t r u c t u r a l m o d u lations a c c o m p a n y i n g c e r t a i n p r e c i p i t a t i o n p h e n o m e n a , will often effectively s u p p r e s s the void s w e l l i n g that o c c u r s in m o s t p u r e m e t a l s as a r e s u l t of d i s p l a c i v e i r r a d i a t i o n with e n e r g e t i c n e u t r o n s , heavy ions or fast e l e c t r o n s . 1-4 A l u m i n u m - c o p p e r alloys in p a r t i c u l a r have l e s s t e n d e n c y to swell u n d e r fast n e u t r o n i r r a d i a t i o n than e l e m e n t a l a l u m i n u m . 1,2 T h e r e is, however, a m a r k e d dependence of the s w e l l i n g r e s i s t a n c e upon the m o r p h o l o g i c a l f o r m and d e n s i t y of the p r e c i p i t a t e . The finest s c a l e p r e c i p i t a t i o n (GP zones) i m p a r t s the s t r o n g e s t s w e l l i n g r e s i s t a n c e to the alloy, t The m e c h a n i s m or m e c h a n i s m s r e s p o n s i b l e for the i n c r e a s e d swelling r e s i s t a n c e of the alloys have not b e e n e x a m i n e d in d e t a i l . In this p a p e r we e x a m i n e the s w e l l i n g r e s i s t a n c e of one A1-Cu alloy c o n t a i n i n g a s i n g l e type of p r e cipitate, 0'. The 0' p r e c i p i t a t e is plate type with b r o a d faces on the m a t r i x cube p l a n e s , and has n o m i n a l composition CuAle. T h i s p r e c i p i t a t e has a s m a l l m i s m a t c h with the m a t r i x on its b r o a d faces and a large m i s m a t c h n o r m a l to the b r o a d f a c e s . It is t e r m e d s e m i c o h e r e n t when few or no d i s l o c a t i o n s a r e p r e s e n t on the b r o a d f a c e s . The m i c r o s t r u c t u r e of the alloy was e x a m i n e d before and a f t e r fast n e u t r o n i r r a d i a t i o n , and the r e s u l t s of the m i c r o s t r u c t u r a l a n a l y s i s w e r e used to a n a l y z e the s w e l l i n g b e h a v i o r in t e r m s of the c h e m i c a l r a t e t h e o r y of void growth. It was found that the s w e l l i n g magnitude can be q u a n t i t a t i v e l y accounted for if the p r e c i p i t a t e - m a t r i x i n t e r faces a r e taken to contain t r a p p i n g s i t e s for both v a c a n c i e s and s e i f - i n t e r s t i t i a l s , thus i n c r e a s i n g the inR. W.CARPENTERand M. H. YOOare withMetalsand CeramicsDivision, Oak RidgeNationalLaboratory,Oak Ridge,TN 37830. 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 A/ME. METALLURGICALTRANSACTIONSA
d i r e c t r e c o m b i n a t i o n rate for point defects and r e d u c ing t h e i r c o n c e n t r a t i o n in the alloy l a t t i c e . E X P E R I
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