Irradiation behavior of Fe-Cu model alloys analyzed with the positron annihilation lifetime technique

The positron annihilation lifetime technique has been employed to investigate the role of nano-sized copper precipitate formation in the irradiation embrittlement of Fe-Cu model alloys with 0.15 wt.% and 1.0 wt.% copper. The samples were irradiated with a 3.0 MeV proton to a dose of 10-3 dpa (displacement per atom) below 353 K. Positron lifetime and micro-Vickers hardness were measured at the as-irradiated state and after annealing at 523 K for 30 min. Positron lifetime measurements were performed with a lifetime spectrometer with a time resolution of about 230 ps (FWHM) and a positron source of 22Na (0.7 MBq). The microhardness change after irradiation clearly showed irradiation-induced hardening. The lifetime spectrums were decomposed into two lifetime components. The longer lifetimes showing the formation of three-dimensional vacancy clusters (microvoid) depend on the Cu content. These results suggest that the irradiation-induced vacancies are incorporated into the copper precipitates. (orig.)