Kinetics of High-Temperature Corrosion in Austenitic Steel Alloys from First Principles

Manufacturers of internal combustion engines seeking to optimize performance and efficiency design their components to operate at temperatures upwards of 700 °C. Under these extreme conditions, corrosive gases resulting from incomplete combustion reactions can drive the formation of a multilayered oxide film atop austenitic steel alloys which would be resistant at lower operating temperatures. In this work, we use density functional theory (DFT) calculations to evaluate the migration energy barrier of point defects in each phase of the oxide film to understand the atomistic mechanisms by which the corrosion process progresses. Particular attention is directed towards the MnCr₂O₄ spinel layer which has been observed experimentally to form rapidly and in direct contact with the alloy - mediating the flow of cations and oxidizing agents between the alloy and oxide film. These DFT results are extended to conditions representative of the application environment through the use of an ab-initio thermodynamics framework which translates the effects of finite temperature and pressure into adjustments of chemical potential.<br/> <br/>This work was supported by the US Department of Energy Office of Energy Efficiency and Renewable Energy Project Number 1919-1744.