PRECIPITATION IN A CU-0.55 WT-PERCENT CR ALLOY

A detailed study was made of the crystallography and strain field contrast at chromium needles precipitated in a Cu-0,55 wt.% Cr alloy. The orientation relationship between the Cu matrix and Cr needles was found to be Kurdjumov-Sachs, with a 〈651〉Cu growth axis being preferred. The strain field of the needles was shown (to a first approximation) to have the same character as that of a dislocation dipole: using this analogy a reasonable match between experimental and computed images was obtained. The magnitude and direction of the Burgers vector of the dislocation dipole suggest complete coherence between the b.c.c. Cr and f.c.c. Cu phases. Experimental evidence for the nature of the precipitate in the early stages of ageing is presented, and the implications of the results for nucleation in this system are considered. © 1979.