Comparison of microstructure evolution in Fe2+ or neutron-irradiated T91 at 500°C

The objective of this study is to evaluate dose rate effects on microstructure evolution in ferritic-martensitic alloy T91 following neutron or Fe2+ irradiation to a common dose (3 dpa) and temperature (500 degrees C). Characterization via TEM and APT is also conducted following Fe2+ irradiation to 100 dpa at 500 degrees C. Dislocation loop morphologies are consistent following each irradiation to 3 dpa, with only minor growth observed at 100 dpa. Each irradiation exhibits favorability for a < 100 > loops over a/2 < 111 >. Si-Mn-Ni-rich and Cu-rich nanoclusters are more coarsely distributed following Fe2+ irradiation, while the same solutes exhibit strong evidence of segregation to grain boundaries, dislocation loops, and dislocation lines following both irradiations to 3 dpa. However, after 100 dpa, solutes are likely redistributed. While the invariance theory likely explains dislocation loop evolution with variations in dose rate, it is not sufficient to predict temperature shift requirements for solute cluster evolution at 3 dpa.