Effects of Re content and fabrication process on microstructural changes and hardening in neutron irradiated tungsten

The effects of the material fabrication process and rhenium (Re) content on the irradiation-induced changes in the microstructure and hardness of pure tungsten (W) and WRe alloys were investigated. Neutron irradiation of pure Wand WRe alloys (Re concentration 326%) was carried out in the experimental fast reactor JOYO. The irradiation conditions were 0.44 displacement per atom (dpa) at 531°C and 0.47 dpa at 583°C for pure W and WRe alloys, respectively. After irradiation, microstructural observations using a transmission electron microscope (TEM) and Vickers microhardness tests were performed. Voids and dislocation loops were observed in both pure Wand WRe alloys after irradiation. The number density of voids in pure W was higher than that in W3% Re, W5% Re and W10% Re. Only in the case of W26% Re irradiated to 0.47 dpa at 583°C were there no voids observed, but irradiation-induced fine precipitates and a few dislocation loops were observed. The irradiation hardening of pure W was greater than that of the WRe alloys. It was considered that irradiation hardening of pure W was caused mainly by the higher number density of voids. The addition of Re suppressed void formation and irradiation hardening of the WRe alloys. Irradiation hardening of W was also suppressed in hot-rolled W compared with arc-melted as-cast W.