Part I: Theoretical Predictions of Preferential Oxidation in Refractory High Entropy Materials

TL;DR

This paper uses thermodynamic methods to predict preferential oxidation in refractory high entropy materials, highlighting potential stability issues and phase changes that could affect their high-temperature performance.

Contribution

It provides a systematic thermodynamic analysis of oxidation behavior and preferential oxidation effects in refractory high entropy alloys and ceramics, which was previously not well understood.

Findings

Large tendency for preferential oxidation in high entropy alloys.

Reduced preferential oxidation effects in carbides.

Potential destabilization of solid solutions due to oxidation.

Abstract

High entropy materials, which include high entropy alloys, carbides, and borides, are a topic of substantial research interest due to the possibility of a large number of new material compositions that could fill gaps in application needs. There is a current need for materials exhibiting high temperature stability, particularly oxidation resistance. A systematic understanding of the oxidation behavior in high entropy materials is therefore required. Prior work notes large differences in the thermodynamic favorability between oxides formed upon oxidation of high entropy materials. This work uses both analytical and computational thermodynamic approaches to investigate and quantify the effects of this large variation and the resulting potential for preferential component oxidation in refractory high entropy materials including group IV-, V- and VI-element based alloys and ceramics. Thermodynamic calculations show that a large tendency towards preferential oxidation is expected in these materials, even for elements whose oxides exhibit a small difference in thermodynamic favorability. The effect is reduced in carbides, compared to their alloy counterparts. Further, preferential oxidation in high entropy refractory materials could result in possible destabilization of the solid solution or formation of other, competing phases, with corresponding changes in bulk material properties.