Microstructural evolution in helium doped HT-9 ferritic steel following 14 MeV nickel ion irradiation

A set of HT-9 specimens uniformly pre-implanted with 100 appm of helium up to a depth of 1.3 μm were irradiated with 14 MeV nickel ions up to 60 dpa at temperatures of 400, 500 and 6000C. Cavities were observed in the He-doped specimens irradiated at 500 and 6000C. The maximum local swelling was found to be 0.1% in the specimen irradiated at 5000C to 60 dpa. There was no measurable difference in precipitate evolution and dislocation loop structure between samples irradiated with and without pre-implanted helium. It is concluded that free gas atoms are essential to the formation of cavities in heavy ion irradiated HT-9. The overall low swelling characteristics of this alloy show that HT-9 is a highly swelling resistant material even in the presence of considerable amounts of helium. (orig.)