Microstructural evolution on Ti-modified austenitic stainless steel irradiated by high energy proton

Hamaguchi, Dai; Kikuchi, Kenji; Saito, Shigeru   ; Endo, Shinya; Yong, D.*

The microstructural evolutions on austenitic stainless steel JPCA irradiated in SINQ target was investigated. JPCA is Ti-modified type-316 base austenitic stainless steel for reduced swelling, and is one of the candidate materials for the structural material on Japanese ADS. Specimens were irradiated in STIP-I and STIP-II with 580MeV proton. For the sample irradiated to 5.7dpa at 150C on STIP-I, only high density of small loops and black dot defects were observed. The density of the loops did not increase significantly with doses and temperatures, which was around 710m, but the size increased from around 15nm at 5.7dpa to 25nm at 19.5dpa on STIP-II irradiated sample. On the other hand, formation of high density small He bubbles with a size of about 2 to 3nm and a density around 1 to 410m were observed for the samples irradiated more than 7.9dpa at above 200C. The densities of the bubbles did not significantly change with doses but the sizes slightly decreased. The helium concentration for the sample with the dose of 7.9dpa was about 600appm, and for the highest dose sample with 19.5dpa was about 1600appm. The formation of bubbles on JPCA was observed at lower temperature compared to EC316LN on STIP-I irradiated samples. This might due to the Ti modification, since Ti in steel is known to be an over-size element and prefer to combine with vacancies, which leads to shorten the incubation period for cavity formation.