Microstructure evolution of T91 irradiated in the BOR60 fast reactor

Microstructures of T91 neutron irradiated in the BOR60 reactor at five temperatures between 376 degrees C and 524 degrees C to doses between 15.4 and 35.1 dpa were characterized using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and atom probe tomography (APT). Type a < 100 > dislocation loops were observed at 376-415 degrees C and network dislocations dominated at 460 degrees C and 524 degrees C. Cavities appeared in a bimodal distribution with a high density of small bubbles less than 2 nm at irradiation temperatures between 376 degrees C and 415 degrees C. Small bubbles were also observed at 460 degrees C and 524 degrees C but cavities greater than 2 nm were absent. Enrichment of Cr, Ni, and Si at the grain boundary was observed at all irradiation temperatures. Radiation-induced segregation (RIS) of Cr, Ni and Si appeared to saturate at 17.1 dpa and 376 degrees C. The temperature dependence of RIS of Cr, Ni and Si at the grain boundary, which showed a peak Cr enrichment temperature of 460 degrees C and a lower peak Ni and Si enrichment temperature of similar to 400 degrees C, was consistent with observations of RIS of Cr in proton irradiated T91, suggesting that the same RIS mechanism may also apply to BOR60 irradiated T91. G-phase and Cu-rich precipitates were observed at 376-415 degrees C but were absent at 460 degrees C and 524 degrees C. The absence of G-phase at 524 degrees C could be related to the minimal segregation of Ni and Si in that condition. (C) 2018 Elsevier B.V. All rights reserved.