Cu-Cr合金におけるCr粒子の転位上優先析出

Abstract

Upon precipitation of a second phase from a solid matrix crystal, dislocations frequently act as preferential nucleation sites. It is well known that internal and external stresses promote the formation of preferential variants of precipitates. It is therefore reasonable to consider that stress fields around a dislocation play an essential role on the variant selection of precipitates. The present research is aimed to quantitatively evaluate the role of the stress fields around a dislocation on the preferential formation of specific precipitate variants. Solution-treated Cu-0.32 mass%Cr alloys were deformed in tension by 5%. To form Cr precipitate particles, the deformed specimens were aged at 773 K for 1.8 ks and successively aged at 973 K for 1.8 ks. To characterize variants of Cr particles and dislocations, thin foils sliced from the aged specimens were observed by using a transmission electron microscope. From analysis of selected-area diffraction patterns, it is revealed that only a certain Kurdjumov-Sachs variant of Cr particles among the 24 crystallographically equivalent ones is formed on given dislocations. By considering the interaction between transformation strains upon precipitation and stress fields around dislocations, it is successfully explained that the specific Cr variants are formed preferentially on the given dislocations.