目的 提高AlMo0.5NbTa0.5TiZr难熔高熵合金的抗氧化性能。方法 采用非自耗真空电弧熔炼法制备了AlMo0.5NbTa0.5TiZrBx（x=0、0.02、0.06）难熔高熵合金，通过系列高温氧化试验、X射线衍射分析和扫描电镜及能谱分析，研究了微量B元素的添加对该合金组织结构和高温氧化性能的影响规律。结果 铸态AlMo0.5NbTa0.5TiZr合金具有典型的枝晶状凝固组织，包括由黑色枝晶间区的富Al-Ti-Zr的BCC1相、明亮枝晶区的富Mo-Nb-Ta的BCC2相以及枝晶边缘灰色过渡区的富Al-Zr相。微量B的添加没有改变AlMo0.5NbTa0.5TiZr相组成，但使合金的枝晶组织明显细化。添加B以后，AlMo0.5NbTa0.5TiZrBx合金的放热峰强度由0.95 W/g降至0.05 W/g，氧化反应的峰值温度由880 ℃升至1020 ℃；添加适量的B可改善合金短时氧化过程中的氧化皮剥落现象，并可防止合金在长时氧化过程中出现灾难性氧化。由于B的添加，AlMo0.5NbTa0.5TiZrB0.06合金表面在800 ℃氧化50 h过程中形成了Nb4Ta2O15和AlNbO4等具有保护性的复杂氧化物。结论 添加适量的B元素不仅可抑制AlMo0.5NbTa0.5TiZr合金在800~1200 ℃之间的氧化反应和氧化增重程度，而且可以大幅提高合金在800 ℃+3 h和800 ℃+50 h条件下的氧化抗力。

The work aims to improve the high temperature oxidation resistance of AlMo0.5NbTa0.5TiZr refractory high- entropy alloys, AlMo0.5NbTa0.5TiZrBx (x=0, 0.02, 0.06) refractory high-entropy alloys were prepared by a non-consumable vacuum arc melting technology and the effects of B on the microstructure and high temperature oxidation resistance were investigated by a series of high temperature oxidation experiments, XRD, SEM-BSE and EDS. The results show that the microstructures of as-cast AlMo0.5NbTa0.5TiZr alloy has the characteristic of dendritic morphology with Al-Ti-Zr rich BCC1 phase in black interdendritic zone, Mo-Nb-Ta rich BCC2 phase in bright dendritic zone and Al-Zr rich phase between the dendritic zone and the interdendritic zone. The addition of trace amounts of B (x=0.02 and x=0.06) does not change the phase composition but refine the dendritic structure of the alloy. For the addition of B with x=0.06, the exothermic peak value decreases from 0.95 W/g to 0.05 W/g, whereas the peak temperature for oxidation reaction increases from 880 ℃ to 1020 ℃. B addition can alleviate the exfoliation of the oxidation film formed in the process of the short-term oxidation and prevent the disastrous oxidation of AlMo0.5NbTa0.5TiZr alloy during long-term oxidation. Oxidized at 800 ℃ for 50 h, the complex protective oxidation layer with Nb4Ta2O15 and AlNbO4 are formed on the surface of AlMo0.5NbTa0.5TiZrB0.06. Therefore, B addition can not only obviously reduces the oxidation weight gain rate but also greatly enhance the oxidation resistance of the alloy oxidized at both 800 ℃ for 3 h and 800 ℃ for 50 h.