Oxide Scale Evolution on Binary Alloys: Transient State Kinetics from First Principles

Abstract

Metal oxidation is a major cause of structural materials degradation. Alloying has been a successfully strategy to mediate metal degradation by forming protective oxides of minor elements. Understanding factors that affect the formation of such a protective film is essential for the rational design of corrosion resistant alloys. The Wagner theory focused on oxygen permeability and metal diffusion in the alloy beneath the oxide scale. Cation kinetics in the oxides is also important for the oxide composition evolution and thus the protective layer formation, which was missing in previous models. In this work, we study the competing cation diffusion and segregation dynamics in the oxide from first principles. By doing so, we are able to predict the oxide composition as a function of time with atomic resolutions at different conditions. Effective cation diffusivities through the oxide film can be obtained as a function of composition as well, which quantifies the protectivity of the oxide. Comparison will be made between alumina former and chromia former in Ni based alloys and steel.In our approach, energetics of various local configurations is calculated from DFT+U and parameterized into a surrogate model by cluster expansion. Hopping barriers are calculated from the nudged elastic band method. The above two are combined by the Bell–Evans–Polanyi (BEP) relation to provide essential inputs for kinetic Monte Carlo simulations. This approach enables large length scale and long-time scale atomistic kinetic simulations with the quantum level of accuracy.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract Number DEAC52-07NA27344. IM release number: LLNL-ABS-810184