Thermodynamic Stability of Oxide Phases of Fe-Cr Based ODS Steels via Quantum Mechanical Calculations

Using density functional theory-based calculated formation and reaction enthalpies, we have examined the relative stability of a large number of likely oxide phases of typical oxide dispersion strengthened steels based on the Fe-Cr-Al-Ti-Y-O system. Calculated formation and reaction enthalpies are in good agreement with available measured values. The relatively more negative formation enthalpies of Y2O3, Y2TiO5, Y4Al2O9, Y2Ti2O7 and YAlO3 oxides show them to be more stable corroborating with their observation in the microstructure of ODS steels. Analysis of reaction enthalpies, guided by convex-hull consideration, gives a mechanism by which reactions of Y2O3 with Al2O3 for the formation of YAlO3, Y4Al2O9, and Y3Al5O12, and reactions of Y2O3 with TiO2 for the formation of Y2TiO5 and Y2Ti2O7, are favored over other likely reactions, such as, those based on Y-Fe-O, Y-Cr-O and Fe-Cr-O systems.