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

Abstract The cavity depth distributions in advanced ferritic/martensitic and austenitic 316 steels were characterized following irradiation with Ni ions at 580 oC to peaked damage of ∼ 300 dpa and 13000 appm pre-implanted helium. The swelling depth distributions for the 316 austenitic steel were determined to ∼ 0.0148%/dpa in helium pre-irradiation 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 pre-irradiation region. For the RAFM steel, compared to the transitional and peak regions, pre-injection helium promoted helium bubble nucleation and assisted swelling in the advanced ferritic/martensitic steel. Meanwhile, for the 316 steel, pre-injection helium not only promoted nucleation of cavities but also retarded the swelling by depressing the growth of size and enhancement nucleation of small cavities.