Phase-Field Modeling of Conditions Leading to Protective Oxide Scale Formation

One of the most demanding properties for reliable high temperature structural materials is oxidation resistance. The transition from internal to external oxidation is often a basis for alloy design to slow down the oxidation process. While lots of experimental efforts have been devoted to investigating the transition, there is still a significant gap in understanding the relevant mechanisms. This can be partly attributed to a lack of physics-based modeling capabilities due to the difficulty in constructing a coherent and consistent thermodynamic framework for oxidation modeling in multi-component alloy systems and the complexity of the interplay among the various governing factors for oxidation – a rich topic for Integrated Computational Materials Engineering. To bridge this gap, one of the tasks in the on-going XMAT project sponsored by US-DOE that involves 7 National Laboratories is to develop a phase-field modeling capability for an alloy system where the oxidation transition can be simulated. In this presentation, we will describe a phase-field model for a ternary prototype system where competition of a faster-growing oxide and a thermodynamically-more-stable oxide can be considered. The model captures the oxidation reactions at the surface and in the bulk, as well as the interdiffusion of oxygen and other elements. The application of this model to investigate internal to external oxidation transition will be discussed.