It was noted that, upon precipitation of a second phase from a solid crystal matrix, dislocations frequently acted as preferential nucleation sites. It was well known that internal and external stresses promoted the formation of preferential variants of precipitates. It was therefore considered that stress fields around a dislocation played an essential role in variant-selection for precipitates. The present work was aimed at quantitatively evaluating the role played, by stress fields around a dislocation, in the preferential formation of specific precipitate variants. Solution-treated Cu-0.32wt%Cr

alloys were deformed in tension by 5%. In order to form Cr precipitates, the deformed specimens were aged (773K, 1800s) and then aged again (973K, 1800s). Thin foils were sliced from the aged specimens and observed by transmission electron microscopy. From analyses of selected-area diffraction patterns, it was deduced that only a certain Kurdjumov-Sachs variant among the 24 crystallographically equivalent Cr particles was formed on a given dislocation. By considering the interaction between transformation strains during precipitation, and stress fields around dislocations, it could be explained why specific Cr variants formed preferentially on certain dislocations.

Preferential Precipitation of Cr Particles on Dislocations in a Cu-0.32wt%Cr Alloy. T.Fujii, M.Ogawa, S.Onaka, M.Kato: Journal of the Japan Institute of Metals, 2002, 66[10], 989-96