Performance of high-Cr ODS steels under high-temperature neutron irradiation
Two ferritic Oxide Dispersion Strengthened (ODS) steels Fe-12Cr-YWT and Fe-14Cr-YWT were irradiated in the High Flux Reactor (HFR) up to 3 dpa at a nominal temperature of 600°C. Tensile tests at room and elevated temperatures as well as microstructural investigations using transmission electron microscopy (TEM) and atom probe tomography (APT) were performed to study evolution of the ODS steels during the high-temperature neutron exposure. Both steels had similar responses to the neutron irradiation in HFR. Tensile testing demonstrated very little effect of irradiation on strength and plasticity. STEM studies showed stable fine distribution of Ti-Y oxides before and after irradiation, with larger sized precipitates at grain boundaries (10-30nm) and smaller precipitates within the matrix (<10nm). APT measurements confirmed high stability of Y-based oxides with relatively small increase of the average diameter (about 20%) after irradiation and stable number density of the clusters. STEM-EDX analysis revealed the presences of W-rich Laves phase precipitates at grain boundaries formed during the neutron exposure in HFR. Besides, a higher number density of Cr rich carbides was observed in the Fe-12Cr-YWT steel after irradiation. A 50% drop in matrix W content was measured by APT that is consistent with the TEM observations of W-rich Laves phases at GBs.