High-resolution electron microscopy was used to study the structure of Cu-rich precipitates in an alloy that had been irradiated with 2.5MeV electrons at 295C to a dose of 3.1 x 1023/m2 (0.0014dpa) at a dose-rate of 4.1 x 1017/m2s (2 x 10-9dpa/s). Most of the precipitates which were smaller than about 8nm in diameter were found to have a twinned 9R structure which was similar to that seen in thermally aged alloys. Some precipitates which were larger than about 8nm in diameter appeared to have transformed entirely or partially to a 3R or face-centered cubic structure. The results confirmed that the main effect of irradiation was to enhance the diffusion of Cu. The smaller size at which the 9R to 3R to face-centered cubic transformation appeared to occur under irradiation was attributed to the incorporation of vacancies into the precipitates or to the nucleation of small dislocation loops at the precipitate/matrix interface. Either of these was expected to change the critical size at which the 9R-3R transformation was triggered.

H.A.H.Duparc, R.C.Doole, M.L.Jenkins, A.Barbu: Philosophical Magazine Letters, 1995, 71[6], 325-33