Effect of Al content on the oxidation behavior of refractory high-entropy alloy AlMo0.5NbTa0.5TiZr at elevated temperatures

The effects of Al content on the oxidation resistance of AlMo 0.5 NbTa 0.5 TiZr refractory high entropy alloys (RHEAs) were investigated. The oxidation obeys a power-law passivating oxidation at the early stage, followed by a transformation to linear oxidation. Increasing Al content reduces the mass change of forming the full coverage of passivating scale and prolongs the passivation duration of alloys. Higher Al content benefits the formation of AlNbO 4 and AlTaO 4 instead of Nb 2 O 5 and Ta 2 O 5 , which has a positive effect on oxidation resistance of alloys. The fracture of scales generally occurs at the mass gain of 15 mg∙cm −2 roughly and leads to the transformation to linear oxidation. • The oxidation of Al x Mo 0.5 NbTa 0.5 TiZr obeys a power-law oxidation, followed by a transformation to linear oxidation. • Increasing Al content reduces the mass change of forming passivating scale and prolongs the passivation duration of alloys • Higher Al content benefits the formation of AlNbO 4 and AlTaO 4 and improves the oxidation resistance of alloys.