| Summary: | Oxidation behavior of a refractory AlNbTiVZr<sub>0.25</sub> high-entropy alloy at 600⁻900 °C was investigated. At 600⁻700 °C, two-stage oxidation kinetics was found: Nearly parabolic oxidation (n = 0.46⁻0.48) at the first stage, transitioned to breakaway oxidation (n = 0.75⁻0.72) at the second stage. At 800 °C, the oxidation kinetics was nearly linear (n = 0.92) throughout the entire duration of testing. At 900 °C, the specimen disintegrated after 50 h of testing. The specific mass gains were estimated to be 7.2, 38.1, and 107.5, and 225.5 mg/cm<sup>2</sup> at 600, 700, and 800 °C for 100 h, and 900 °C for 50 h, respectively. Phase compositions and morphology of the oxide scales were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that the surface layer at 600 °C consisted of the V<sub>2</sub>O<sub>5</sub>, VO<sub>2</sub>, TiO<sub>2</sub>, Nb<sub>2</sub>O<sub>5</sub>, and TiNb<sub>2</sub>O<sub>7</sub> oxides. Meanwhile, the scale at 900 °C comprised of complex TiNb<sub>2</sub>O<sub>7</sub>, AlNbO<sub>4</sub>, and Nb<sub>2</sub>Zr<sub>6</sub>O<sub>17</sub> oxides. The oxidation mechanisms operating at different temperatures were discussed and a comparison of oxidation characteristics with the other alloys was conducted.
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