A study on the durability of oxide coatings fabricated on a refractory high entropy alloy

This study investigates the structural features and mechanical durability of the oxide coatings fabricated on HfMoNbTiZr refractory high entropy alloy via micro-arc oxidation in two different electrolytes (namely, sodium silicate- and sodium aluminate-based). Structural characterizations revealed that fabricated coatings consisted of oxides of the refractory elements (Hf, Zr, Nb, Ti) except Mo and the oxides of the main constituents of the electrolyte (Si and Al). According to the results of hardness and scratch tests, the Al₂O₃-containing coating (fabricated in sodium aluminate-based electrolyte) has got higher hardness and scratch resistance compared to SiO₂-containing coating (fabricated in sodium silicate-based electrolyte). Moreover, the SiO₂-containing coating detached from the substrate at 100 °C under sliding contact, while the Al₂O₃-containing coating remained intact with the substrate up to temperature of 300 °C. Therefore, it is concluded that Al₂O₃-containing coating has a potential to provide better protection against sliding contact for the HfMoNbTiZr alloy both at room and high temperatures.