硼对AlMo0.5NbTa0.5TiZr难熔高熵合金组织和高温氧化性能的影响

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。

Effect of B Addition on Microstructure and High Temperature Oxidation Resistance of AlMo0.5NbTa0.5TiZr Refractory High-entropy Alloys

The work aims to improve the high temperature oxidation resistance of AlMo0.5NbTa0.5TiZr refractory highentropy 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.