High temperature oxidation resistance of W-containing high entropy alloys

Tungsten containing refractory high entropy alloys (HEAs) are potential candidate for high temperature applications owing to their remarkable mechanical properties. However, the oxidation resistance of W containing HEAs at high temperatures is problematic, and it received less attention. In this work, several equiatomic W containing WTaTiCr, WMoTaTiCr, WTaAlCr, and WMoTaAlCr refectory HEAs were fabricated by arc melting technique and their oxidation behavior at 1000 °C for 10 h was compared with MoTaTiCr medium entropy alloy (MEA). The as cast microstructure of the MoTaTiCr, WTaTiCr, WMoTaTiCr, and WMoTaAlCr alloys exhibited a single BCC solid solution, while the as cast WTaAlCr MEA showed some extent of intermetallic compounds along with the BCC phase. The best oxidation resistance was obtained for MoTaTiCr MEA, which was protected by a continuous CrTaO4 scale layer. The formation of tungsten oxides (mainly WO3) prohibited the evolution of a protective oxide layer of AlTaO4, CrTaO4 or Al2O3 on the surface of W containing alloys. WMoTaAlCr HEA exhibited the best oxidation resistance among all the W containing alloys, which was protected by a nearly continuous rutile type (Al,Cr)TaO4 oxide layer.