Studies on irradiation effects of ODS steels by using DuET facility

Irradiation hardening and microstructural change of oxide dispersion strengthened (ODS) ferritic steels were investigated by using ion-irradiation technique. The material used for the present study was K3 (16Cr-2W-0.3Ti-4.6AI-0.4Y2O3) ODS ferritic steel for the application to Generation IV concept advanced reactors and fusion reactors. 6.4 MeV Fe3+ ions were used to irradiate to the K3 ODS steel by using a 1.7 MeV tandem accelerator in the DuET facility, Kyoto University. The irradiation temperatures were 300 degree C and 500 degree C. The nominal displacement damage rate and total displacement damage were 1 x 10-3 dpa/s and up to 10 dpa at about 600 nm depth from the irradiated surface, respectively. Nano-indentation hardness was evaluated with a Berkovich indenter. After the ion-irradiation at 300 degree C up to 1 dpa, the normalized nano-indentation hardness (hardness after irradiation/hardness before irradiation) of the K3 ODS steel reached about 1.28 and the value showed no change up to 10 dpa. On the other hand, the ion-irradiation at 500 degree C up to 10 dpa showed no significant irradiation hardening. TEM observation revealed that dense and fine dislocation loops were formed in the ion-irradiated steels at 300 degree C, which were probably enough to explain the irradiation hardening. Effects of helium on the swelling behavior of ODS steels will be also presented in the symposium. (authors)