Thermally induced strain recovery in irradiated and unirradiated zirconium alloy stress-relaxation specimens

Abstract

Thermally induced strain recovery has been measured in specimens which were stress relaxed at 570 K either in a reactor or in an autoclave. Strain recovery occurs in both unirradiated and irradiated specimens. Strain recovery in unirradiated specimens is attributed to unpinning of anelastically bowed dislocations. Strain recovery in irradiated specimens occurs in two stages; a rapid stage attributed to unpinning bowed dislocations and a slow stage attributed to annealing of irradiation defects. Assuming that mechanisms proposed for creep are applicable during stress-relaxation the complete recovery of irradiation-induced strains in annealed specimens and partial recovery in specimens with some cold-work agrees with expectations from models based on stress-induced alignment of dislocation loops and irradiation damage. Recovered strains in this experiment were small as were strains measured by others on irradiated specimens with larger deformation strains, thus annealing to reduce strains in reactor structures may not be useful.