The change in the hardness of LCAC, TZM, and ODS molybdenum in the post-irradiated and annealed conditions

Hardness measurements were performed on wrought Low Carbon Arc Cast (LCAC), TZM, and Oxide Dispersion Strengthened (ODS) molybdenum in the post-irradiated and post-irradiated + annealed condition to determine the recovery kinetics. Irradiations performed in the High Flux Isotope Reactor (HFIR) at nominally 300 °C and 600 °C to neutron fluence levels that range from 10.5 to 246 × 1024 n/m2 (E > 0.1 MeV) resulted in relatively large increases in hardness (77–109%), while small increases in hardness (<18%) were observed for irradiations at 870–1100 °C. The hardness recovery for ODS and LCAC irradiated at 300 °C and 600 °C were shown to be complete at 980 °C and ≈ 1100–1250 °C, respectively. Isothermal annealing at 700 °C was used to determine the activation energy for recovery of LCAC and ODS (3.70–4.88 eV ± 0.28–0.77 eV), which is comparable to values reported in the literature for molybdenum vacancy self-diffusion. This suggests that recovery of LCAC and ODS is controlled by the solid-state diffusion of vacancies in the bulk, and that the finer grain size and particle size ODS does not affect this mechanism. TZM exhibited slower recovery kinetics, which can be explained by the solute atoms (titanium and zirconium) inhibiting vacancy diffusion.