Oxidation Behavior between 700 and 1300 °C of Refractory TiZrNbHfTa High‐Entropy Alloys Containing Aluminum

Refractory alloys without Cr, Al, and Si additions exhibit very poor high temperature oxidation resistance and thus significantly limit their applications. With an aim to improve the poor oxidation resistance of strong and ductile refractory TiZrNbHfTa high‐entropy alloys (HEAs), this study investigates the effect of Al additions on the oxidation behavior and mechanisms for Al_0‐1TiZrNbHfTa HEAs. Higher Al content renders the alloy more resistant to oxidation. The AlTiZrNbHfTa alloy exhibits a mass gain twice of that of conventional Ni‐based alloys at 1100 °C for 1 h, but much less than Nb refractory alloys because an Al‐containing oxide on the surface layer provides a partial barrier against oxidation between 700 and 1100 °C. But, at 1300 °C the Al‐containing alloys exhibit poor oxidation resistance because the less dense oxide layers provide oxygen with an effective diffusional channel and enable oxygen to penetrate the substrate more easily.