Irradiation-induced Cu aggregations in Fe: An origin of embrittlement of reactor pressure vessel steels - art. no. 134110

Very dilute Fe-Cu systems, model alloys of nuclear reactor pressure vessel (RPV) steels, irradiated by fast neutrons, are studied by positron annihila tion experiments and simple calculations. The ultrafine Cu precipitates, wh ich are never formed by thermal aging in the dilute alloys, are observed cl early and are strongly suggested to be responsible for irradiation-induced embrittlement of RPV steels. The formation and recovery process of the prec ipitates an revealed: (i) irradiation-induced Cu-vacancy complexes aggregat e into microvoids; (ii) around 400 degreesC the dissociation of vacancies f rom the microvoids leads to the formation of the Cu precipitates of about 1 nm in size; and (iii) the Cu precipitates anneal out at about 650 degreesC .