Helium cavity formation research on oxide dispersed strengthening (ODS) ferritic steels utilizing dual-ion irradiation facility

A dual-ion irradiation method is one of the most popular techniques for the research of microstructural evolution of materials under fusion environmental conditions. The application of oxide dispersion strengthened (ODS) ferritic steels is anticipated for realization of high temperature operation of fusion reactors above 600 deg. C. In this research, the investigation of the microstructural evolution of high corrosion resistant ODS steels was performed using the ion irradiation methods. Dual ion-irradiation experiments were performed at the DuET facility, Kyoto University using 6.4 MeV Fe self-ion and 1 MeV helium ion. The irradiation temperatures were 300 and 500 deg. C. The dose, dose rate, and helium over dpa ratio were 20 dpa, 5 x 10-4 dpa/s, and 15 appm/dpa, respectively. The post-irradiation experiments were performed using SEM, TEM and the nano-indentation methods. Significant microstructural evolution of grains and oxides were not observed after the single-ion irradiation at 20 dpa, 500 deg. C. Fine helium cavities were observed in the dual-ion irradiated 19Cr-2W-4Al ODS steel. Fine cavities of approximately several nanometers diameter were densely and uniformly formed in dual-ion irradiated range