High-entropy alloys (HEAs) synthesized using refractory elements are being strongly considered as candidates for high temperature structural applications. The role of compositional changes of HEA surfaces due to oxidation is crucial to sustain the material properties, but a detailed description of the thermodynamic mechanism driving the adsorption of oxygen on such complex surfaces is absent. We examine and explain the reaction process of oxygen on a representative refractory HEA surface using first principles and atomistic thermodynamic models. The HEA surface is highly reactive to oxygen yielding a full monolayer coverage at temperatures between 300 and 1500 K. The preferential adsorption of oxygen to specific sites of the HEA surface is attributed to the electronic configuration of the bonding shells of the constituent surface atoms. On further oxygen addition, the oxygen atoms diffuse into the bulk regions of the alloy. Manipulation of temperature and oxygen pressure reveals that it is difficult to rid the alloy surface of oxygen even at extremely low pressures of 10⁻⁹ bar at 2000 K.

使用耐火元素合成的高熵合金（HEA）被强烈认为是高温结构应用的候选材料。氧化引起的HEA表面成分变化的作用对于维持材料的性能至关重要，但是缺少驱动氧在此类复杂表面上吸附的热力学机理的详细描述。我们使用第一原理和原子热力学模型检查并解释了氧气在代表性难熔HEA表面上的反应过程。HEA表面在300至1500 K之间的温度下对氧气具有很高的反应性，从而产生了完整的单层覆盖。氧气优先吸附到HEA表面的特定位置归因于组成表面原子的键合壳的电子构型。进一步添加氧后，氧原子扩散到合金的主体区域中。对温度和氧气压力的操作表明，即使在10的极低压力下，也很难去除合金表面的氧气2000 K时为^-9 bar。