Effect of Nickel Concentration on Radiation-Induced Diffusion of Point Defects in High-Nickel Fe-Cr-Ni Model Alloys during Neutron and Electron Irradiation

The quantitative evaluation of vacancy mobility was conducted by analyzing the void denuded zone (VDZ) width formed near grain boundaries under neutron and electron irradiation. The microstructures of Fe-15Cr-xNi (x = 15, 20, 25, 30 mass%) alloys that were neutron irradiated at 749 K were examined, and the differences in the vacancy mobility among the four alloys were qualitatively investigated. We also investigated the VDZ widths formed under electron irradiation at various irradiation temperatures (576 K-824 K) in these alloys. The VDZ widths increased with increasing Ni content in both the neutron and electron irradiation experiments, which implies an increase of the vacancy mobility. The vacancy migration energies were estimated from the temperature dependence of the VDZ widths, and the estimated energies were 1.09, 0.97, 0.90, and 0.77 eV for the alloys containing 15, 20, 25, and 30 mass% Ni, respectively. It was confirmed that these estimated energies were approximately consistent with the ones estimated by well-known dislocation loop growth rate analysis through electron irradiation experiments. From the obtained vacancy migration energies by the VDZ analysis, the effective vacancy diffusivity and excess vacancy concentration were estimated using the analytical equation of the VDZ width, which quantitatively confirmed the increase of the vacancy mobility with increasing Ni content.