Very dilute Fe-Cu model alloys, for nuclear reactor pressure-vessel steels that were irradiated with fast neutrons, were studied by means of positron annihilation. Ultrafine Cu precipitates, which never formed during the thermal aging of these alloys, were clearly observed and were suggested to be responsible for the irradiation-induced embrittlement of reactor pressure-vessel steels. The irradiation-induced Cu-vacancy complexes aggregated into microvoids. At about 400C, the dissociation of vacancies from the micro-voids led to the formation of Cu precipitates which were about 1nm in size. The Cu precipitates annealed out at about 650C.

Irradiation-Induced Cu Aggregations in Fe - Origin of Embrittlement of Reactor Pressure Vessel Steels. Y.Nagai, Z.Tang, M.Hasegawa, T.Kanai, M.Saneyasu: Physical Review B, 2001, 63[13], 134110 (5pp)