Simulation of high-temperature oxidation in NiCr alloy based on a chemo-mechanical coupled model

Components of gas turbine engines are subjected to severe thermomechanical loads under exposure to aggressive environments containing hydrogen, oxygen, sulfur- and chlorine-based compounds, which induce high-temperature corrosion and subsequent fatigue failure. This type of corrosion is accompanied by interdiffusion of alloy and aggressive components, chemical reactions, finite eigenstrains and rheological strains, necessitating the formulation of a coupled model of these phenomena.The model is developed within the classical irreversible thermodynamics, which incorporates independent mass balance equations for each component and a unified stress tensor. This stress tensor satisfies the mechanical equilibrium condition and depends on both the chemical composition variables and strain measures.The governing equations are formulated in a geometrically nonlinear framework, accounting for elastic, plastic, and viscous components of deformation. The combined approach to diffusion and deformation is employed, which integrates a material-based description of convective transport with a marker-based description of diffusion.A numerical simulation of high-temperature oxidation of nichrome was carried out as a user-defined application within the COMSOL Multiphysics software. The results demonstrate the initiation and growth of a chromium oxide layer accompanied by the development of compressive residual stresses within it.A qualitative analysis of the model in both coupled and uncoupled frameworks, as well as within geometrically linear and nonlinear formulations, revealed significant differences in the distributions of strains and stresses. The geometrically nonlinear formulation captures the oxide front blocking effect, which is attributed to a large gradient in mean stress influencing the diffusion fluxes.The developed model can be applied to describe the evolution of corrosion layers for other types of high-temperature corrosion in heat-resistant alloys.