Precipitation and irradiation damage in proton-irradiated palladium-chromium alloys

Abstract

Irradiation damage of Pd-Cr alloys containing 15, 20 and 25 at % Cr was studied over the temperature range 100 to 550° C, primarily in samples irradiated to a dose of 0.7 d.p.a. The solubility limit in this range of temperatures varies from 22 to 38% Cr, and precipitation of a phase having the L12 crystal structure was observed in unirradiated samples of the 25% Cr alloy aged at temperatures as low as 100° C. Octahedrally shaped voids, with faces parallel to {1 1 1}, were found only in the 25% Cr alloy irradiated from 350 to 550° C, but not in the other alloys at any temperature. The undersized chromium atoms migrate to point-defect sinks during irradiation, resulting in solute segregation and, eventually, precipitation under certain conditions. The precipitation of the L12 phase, which is the thermodynamically stable phase at higher chromium contents, was irradiation-induced at dislocation loops, voids and grain boundaries in the more concentrated undersaturated alloys. This irradiation-induced precipitation was observed in the mid-range and surface regions of the samples containing 20 and 25% Cr, but not in those containing 15% Cr. The behaviour of these alloys is compared with Pd-Fe and Ni-Si alloys, which have also been proton-irradiated in this laboratory, and the similarities and differences are noted and discussed.