First-Principles Kinetic Monte Carlo Modeling of Passivation in Ni-Based Alloys

Abstract

Corrosion by metal oxidation is a major problem for many structural materials, including Ni-based alloys in high-temperature applications. Passivation can be achieved through various alloying strategies, but common theoretical approaches to understanding key factors such as the critical concentration of the minor element are limited in their predictive capability. In particular, existing models often do not explicitly capture competing metal cation migration mechanisms in the oxide. In this study, we examine passivation kinetics of Ni-Cr and Ni-Al alloys by modeling the evolution of initial NiO oxide films as Cr/Al are incorporated. Surrogate models for the energies of various oxide configurations and the migration barriers of metal cations are parameterized from density functional theory calculations. These inputs are used to drive kinetic Monte Carlo simulations over long time scales. By tracking the time-dependent oxidation behavior across alloy composition, we predict critical concentrations of Cr/Al to form continuous passivation layers. Compositional and structural analyses of the simulated oxides are used to quantify fractions of different phases and provide insight into the nature of passivation in each alloy system. The effect of increasing or decreasing the exchange rate of metal atoms near the alloy-oxide interface, which can be related to alloy processing, is also explored. We discuss the applicability of our method to other systems and its incorporation into an existing open-source software package.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.