Coupled Large-Strain Mechanochemical Theory for Solid-State Reaction With Application to Oxidation

Abstract

Oxidation is still perceived as a significant challenge in various industrial applications, e.g., pressurized water reactors and gas-turbines. One of the hurdles in understanding oxidation is its coupled multi-physics nature, i.e., the coupling between mechanics, chemical reaction, change in the microstructure, and diffusion. Here, a general large-strain mechano-chemical theory is developed to model the anisotropic reaction/compositional strain in the solid-state chemical reaction. The anisotropic strain leads to a unique stress relaxation mechanism, which is in agreement with existing experimental studies. This novel stress-relaxation is achieved by introducing a kinetic relationship between deviatoric compositional and reaction deformation rate and the deviatoric Cauchy stress. Also, a new chemical potential, including the deviatoric stress, is derived. The new model shows that mechanical stress alters the chemical equilibrium constant through reaction-induced deviatoric stress. Finally, the developed mathematical framework is used to study the aluminum's oxidation for model verification.