The effect of oversized solute additions on the microstructure of 316SS irradiated with 5 MeV Ni++ ions or 3.2 MeV protons

The effect of the oversized hafnium or platinum (0.3 at.%) solutes on the evolution of irradiated microstructure in 316SS was investigated. Irradiations were conducted with 5 MeV Ni-ions at 500 °C to doses up to 50 dpa or with 3.2 MeV protons at 400 °C to a dose of 2.5 dpa, and previous studies demonstrated that these irradiations are capable of producing similar irradiated microstructure and microchemistry relevant to LWR cores. Microstructures of 316SS, 316SS + 0.3 at.% Pt and 316SS + 0.3 at.% Hf were characterized using transmission electron microscopy. The addition of Hf showed a strong effect in suppressing radiation-induced microstructure evolution; no voids were observed at doses up to 50 dpa for Ni-ion irradiation and 2.5 dpa for proton irradiation. The mean diameter of the Frank loops in the Hf-doped samples is about 40% smaller than loops in 316SS. The microstructural examinations from both types of particle irradiation revealed that for 0.3 at.% Pt addition there is no beneficial effect on irradiated microstructure. The mechanisms for the role of oversize solute additions on the microstructure evolution are discussed.