Depth distributions of cavities in advanced ferritic/martensitic and austenitic steels with high helium preimplantation and high damage level

The cavity depth distributions in advanced ferritic/martensitic and austenitic 316 steels were characterized after irradiation with Ni ions at 580 °C to peaked damage of ~300 dpa and 13,000 appm preimplanted helium. The swelling depth distributions for the 316 austenitic steel were determined to be ~0.0148%/dpa in helium preirradiation region, ~0.1761%/dpa in transitional region, and ~0.0363%/dpa in peak region, respectively. Inhibitory effect of swelling was observed in the peaked dpa region due to the defect imbalance. In contrast, high-level heavy ion damage was insufficient to induce the formation of voids in the helium-free region for the advanced ferritic/martensitic steel, but high density of helium bubbles with the swelling rate of ~0.0086%/dpa occurred in the helium preirradiation region. For the reduced-activation ferritic/martensitic steel, in comparison with the transitional and peak regions, preinjection helium promoted helium bubble nucleation and assisted swelling in the advanced ferritic/martensitic steel. Meanwhile, for the 316 steel, preinjection helium not only promoted nucleation of cavities but also retarded the swelling by depressing the growth of size and enhancement nucleation of small cavities.