Change of thermal diffusivity and lattice constants of W-5% Re-HfC alloys irradiated in a fission reactor

W-5% Re-HfC alloys with aimed HfC contents of 0.5, 1 and 3 wt% were fabricated by powder metallurgy. Their thermal diffusivity and lattice constant were measured before and after neutron irradiation at 330 K up to a fast neutron (E>1 MeV) fluence of 1×10²⁴ n/m². Chemical analysis and lattice constant measurements revealed that Hf existed not as HfC but mainly as a solute in the alloys. The thermal diffusivity of the alloys with HfC less than 1% nominal content was higher than that of W-5% Re, specifically at higher temperatures, while the diffusivity of the alloy with 3% HfC (nominal content) was lower than that of W-5% Re. Only the alloy with 3% HfC showed a distinct decrease of the thermal diffusivity after neutron irradiation and its recovery after annealing. The lattice constants of the W-5% Re alloys increased with the increase of the Hf content. Only the lattice constant of the alloy with 3% HfC represented a considerable increase after neutron irradiation.