Effects of helium on irradiation response of reduced-activation ferritic-martensitic steels; Using nickel isotopes to simulate fusion neutron response

Kim, B. K.*; Tan, L.*; Sakasegawa, Hideo   ; Parish, C. M.*; Zhong, W.*; Tanigawa, Hiroyasu*; Kato, Yutai*

Understanding the effects of helium on microstructures and mechanical properties of reduced-activation ferritic-martensitic steels is important to use of these steels in fusion reactor structures. 9Cr-2WVTa steels were doped with Ni and Ni isotopes at 2 weight percent to control the rate of transmutation helium generation. The samples were irradiated in the High Flux Isotope Reactor. Transmission electron microscopy revealed a variety of precipitates and the radiation-induced dislocation loops and cavities (voids or helium bubbles). Tensile tests of the irradiated samples at the irradiation temperatures showed radiation-hardening at 300C and radiation-softening at 400C. Analysis indicates that the hardening primarily originated from the loops and cavities. The Ni-doped samples had greater strengthening contributions from loops and cavities, leading to higher hardening with lower ductility than the Ni-doped samples. The greater helium production of Ni did not show pronounced reductions in ductility of the samples.