Ab-initio Calculation of Diffusion of Atomic Oxygen in Nickel : Insertion and Substitution of Oxygen in Nickel

Nickel and nickel base alloys have been widely used as structural materials in nuclear systems because they have good mechanical properties at high temperature, high pressure and high corrosion resistance in oxidizing environment. Recently, however, these materials have shown to be suffered from the environment-assist cracking (EAC) such as primary water stress corrosion crack (PWSCC) in pressurized water reactor environments. SCC is a cracking phenomena because of a process involving conjoint corrosion and strain of a metal due to residual or applied stressed within the susceptible environment. Many experimental studies have been performed to reveal the governing mechanism of PWSCC of nickel base alloys and have drawn several different arguments with some possible ways to reveal the process and prevent them, such as oxide rupture, accumulation of critical crack tip strain or hydrogen induced cracking. However, there is no general theory to explain the PWSCC of nickel base alloys, because the experiments of SCC usually take a lot of times, have difficulty to make specific environment of nuclear power plants water chemistry, and the corrosion (or oxidation) process takes place slowly in tiny localized area. Meanwhile, according to the increase in the computer calculation speed, atomistic modeling and simulation method has been receiving much attention as a method to evaluate the mechanical properties, thermodynamics and kinetics characteristics of metals and alloys. Very recently, modeling and simulation studies have been performed to understand the fundamental mechanism of nickel and nickel base alloy corrosion (oxidation) process in high temperature water. For pure nickel, Grruchet et al evaluated diffusion of oxygen in nickel by the variable charge molecular dynamics, and Goerge A. Young et al and Meg-chiche evaluated the diffusion of oxygen in nickel using the ab-initio (first-principle) calculation. Also, Finnis et al and Lozovoi et al calculation explored some properties about oxidation of bimetal such as NiAl. All of them have compared the computational data with the experimental data and the results have shown good agreement. Still, however it is not enough to understand the corrosion behavior detail and to prove the accuracy of the computational results. The purpose of this study is to understand the oxidation behavior of nickel base alloys through the simulation of diffusion processes of oxygen in nickel. Therefore the diffusivity and solubility of oxygen in nickel followed by previous study was calculated. And, the vacancy formation energy of nickel was calculated and the calculation of insertion and substitution energy of oxygen in nickel was performed. Furthermore, this method will be applied to atomistic oxygen diffusion in nickel -chrome binary alloy