Microstructural evolution of proton irradiated T91

Understanding radiation effects in ferritic-martensitic alloys is critical for their success in advanced reactor and transmutation systems. The objective of this work is to evaluate the microstructural and mechanical property changes in irradiated ferritic-martensitic alloy T91. Irradiations were conducted with 2.0 MeV protons to doses of 3, 7, and 10 dpa at a dose rate of 2 × 10^-5 dpa/s and at temperatures of 400 °C, 450 °C, and 500 °C. The post irradiation microstructure contained a high density of black-dots and a₀〈1 0 0〉 dislocation loops in addition to precipitates and tangled dislocations that were present in the unirradiated condition. The irradiated dislocation microstructure is sensitive to the heat treatment. Results show that the irradiated microstructure did not contain any voids or evidence of second phase formation. Hardness increases with dose and tends to saturate around 5 dpa for 400 °C irradiation. Only a portion of irradiation hardening can be accounted for by the observable microstructural features. An initial investigation of the effect of irradiation on prior austenite grain boundary microchemistry revealed that Cr is enriched by 4.7 wt%, V by 0.6 wt% (nearly 300%), and Fe is depleted by 5.3 wt% relative to the bulk values. No segregation was observed in the unirradiated condition. No radiation-induced segregation was observed at martensite lath boundaries. Overall, the irradiated microstructure is consistent with reactor and spallation system experiments.