Effects of Neutron Irradiation and Thermal Annealing on Model Alloys using Positron Annihilation Techniques

We present the results of a systematic investigation of neutron-irradiated and thermally-annealed model alloys using positron annihilation spectroscopy (PAS), including both lifetime and Doppler broadening techniques. The objective of this work is to use PAS to provide information on the irradiation-induced microstructural features that are thought to cause embrittlement in pressure-vessel steels. Such information could complement the results obtained by other techniques, especially small-angle neutron scattering (SANS) and atomic probe field ion microscopy (APFIM). We examined a series of model Fe-based alloys, in which the Cu, P and Ni concentration were systematically varied. These alloys were examined in the as-fabricated state, after irradiation to 1 x 10 19 nxcm-2, and to 8 x 10 19 nxcm-2, and after successive post-irradiation 30-minute isochronal anneals at temperatures ranging from 200 to 600 °C. In each case, we measured the positron annihilation lifetime distribution, the Doppler broadening (S-parameter), and the 15 N Rockwell hardness for the samples.