3D atom probe observation of heavy ion irradiated model alloys for reactor pressure vessel steels

More accurate prediction of neutron irradiation embrittlement of reactor pressure vessel (RPV) steels is very important issue at the high neutron fluence region for the long-term operation of light water reactors. Accelerated irradiation is a useful technique for investigating embrittlement at the high fluence region but requests careful evaluation taking account of flux effects on embrittlement. In this study, solute-atom clusters in heavy ion-irradiated model alloys representative RPV steels are observed using three dimensional atom probe technique, and microstructural changes under highly accelerated irradiation are investigated. Main results are as follows. In Fe-Cu-Ni-Si alloys, ultra fine solute-atom clusters with approximately 2nm are densely formed due to Fe ion-irradiation and consist of Cu, Ni, Mn, and Si. The clusters in Fe ion-irradiated alloys are much smaller and denser than that of neutron irradiated alloys. In addition, the clusters in Fe ion-irradiated alloys have less Cu content and more Ni and Si contents but composition as a whole are nearly same as that of neutron irradiated alloys. There is non-uniformity of concentrations of solute atoms in Fe ion-irradiated alloys. Square root of volume fraction of clusters in Fe ion-irradiated alloys can be almost linear-correlated with changes in hardness. (author)