Hardness and electrical resistivity of molybdenum in the post-irradiated and annealed conditions

Hardness and electrical resistivity were measured for LCAC molybdenum following irradiation at 270-1100 °C and neutron fluences of 10.5-64.4 × 10²⁴ n/m² (E > 0.1 MeV) to provide a basic assessment of the influence of irradiation and post-irradiation annealing on recovery. Hardness was a more sensitive measure of defect density than electrical resistivity. Irradiation at 935-1100 °C resulted in little hardening and therefore no recovery was observed. Recovery of the radiation hardening for molybdenum irradiated at 270-605 °C was observed to begin at Stage V recovery temperatures (≈600 °C) and was completed at 980 °C and 1100 °C, respectively. Isothermal annealing was performed at 700 °C and Meechan-Brinkman analysis indicated that the activation energy for recovery was 4.07-4.88 eV ± 0.83 eV, which is comparable to values for molybdenum self-diffusion. These results indicate that the recovery of molybdenum irradiated at temperatures ≤605 °C occurs by the solid-state diffusion of vacancies to coarsen the dislocation loops and voids.