  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.
