Atomistic Modeling of Interstitial Diffusion of Oxygen in Nickel Chromium Binary Alloy

Nickel and nickel base alloys have been widely used as structural materials in nuclear power systems, because they have favorable material properties at high temperature water environment. Recently, however, these materials have shown to be suffered from primary water stress corrosion cracking (PWSCC) in pressurized water reactor environments. But there is no general theory to explain the mechanism of PWSCC in nickel base alloys, because the process of PWSCC usually takes place slowly in tiny localized area and many difficulties to maintain specific environment of nuclear power plants chemistry are involved. In this study, ab-initio calculations on the diffusion processes of oxygen in nickel and Ni-Cr binary alloy are conducted to understand the oxidation behavior of nickel base alloys. Total energies, forces, and energy profiles are calculated using the density functional theory (DFT) in this study. Then, the cohesive energy, insertion energy of atomic oxygen and vacancy formation energy in nickel are calculated and compared with experimental data. The activation energy of oxygen which is important parameter to understand the diffusion behavior, are also calculated. The results are good agreement with previous work for the diffusion of oxygen in pure nickel. However, the calculated activation energy for diffusion of oxygen in Ni-Cr binary alloy showed lower value than that in nickel because of current limitation of calculational model in this study. The current model will be improved by further investigation considering oxide formation.