Refractory high entropy alloys (RHEAs) hold the promise of superior mechanical properties at high temperatures but are plagued by a lack of oxidation resistance. In this work, the role of Al additions (4.8, and 13 at.%) to HfNbTaTiZr is explored as a means of improving protective oxide scale formation in RHEAs. Oxide formation was resolved using STEM-EDS/EELS, precession electron diffraction, and computational predictions of formation energy. Our results show that oxides with large negative formation energies (i.e., HfO₂/ZrO₂) always formed near the metal/oxide interface while Al₂O₃ and oxides with less negative formation energies formed near the surface. The addition of Al prevented pesting in both alloys and formed Al₂O₃ with 13 at.% Al. While the Al₂O₃ formed was not continuous, we report the lowest threshold yet to prevent pesting with only 4.8 at.% Al added. These findings provide guidance to future alloy development of Al₂O₃-forming alloys.

难熔高熵合金 (RHEA) 有望在高温下具有优异的机械性能，但受到缺乏抗氧化性的困扰。在这项工作中，探索了在 HfNbTaTiZr 中添加 Al（4.8 和 13 at.%）的作用，作为改善 RHEA 中保护性氧化皮形成的一种手段。使用 STEM-EDS/EELS、进动电子衍射和形成能的计算预测来解析氧化物的形成。我们的结果表明，具有大负形成能的氧化物（即HfO ₂ /ZrO ₂）总是在金属/氧化物界面附近形成，而Al ₂ O ₃和具有较小负形成能的氧化物在表面附近形成。 Al 的添加防止了两种合金中的虫害，并形成了含 13 at.% Al 的 Al ₂ O ₃。虽然形成的 Al ₂ O ₃不是连续的，但我们报告了仅添加 4.8 at.% Al 即可防止虫害的最低阈值。这些发现为Al ₂ O ₃形成合金的未来合金开发提供了指导。