Al_(0.5)CrCoFeNi高熵合金高温氧化的研究

采用真空电弧炉在氩气保护下熔炼Al0.5Cr Co Fe Ni高熵合金,在不同温度(800~1100℃)下进行100 h的高温氧化实验,测定其氧化动力曲线,采用X射线衍射仪和扫描电镜等方法分析氧化层结构和形貌。结果表明:Al0.5Cr Co Fe Ni高熵合金在800和900℃形成的氧化膜较完整且致密,具有较为优异的抗氧化性能。在1000和1100℃形成的氧化膜较厚,膜内有大量裂纹与孔洞,抗氧化性能较差。氧化初期,界面反应起主导作用,随着氧化膜的生长,扩散过程发挥越来越重要的作用,成为继续氧化的控制因素,以致一种或多种合金元素氧化物在表面析出,形成尖晶石类内层氧化物Ni Cr2O4、Co Cr2O4、Fe(Cr,Al)2O4内氧化层。在高温氧化过程中,N2会参与反应,与Al发生较强反应,生成Al N颗粒,进一步的氧化过程使Al N再次氧化,N2逃逸,留下具有Al N外形的空洞。

High Temperature Oxidation Behavior of Al0.5CrCoFeNi High Entropy Alloy

Al0.5CrCoFeNi high entropy alloy was prepared by vacuum arc melting in a high-purity argon atmosphere. The oxidation experiments were performed at the temperatures of 800, 900, 1000 and 1100 oC for 100 h, and the corresponding oxidation kinetics curves have been tested. The structure and morphology of oxide layer have been studied by adopting the analytical methods, such as XRD and SEM. The results show that oxide films forming at 800 oC and 900 oC were complete and compact, and have excellent oxidation resistance. However, the oxide films forming at 1000 oC and 1100oC become much thicker and have a large number of cracks and holes, which result into poor oxidation resistance. Interface reactions played a mast role at the early stage of oxidation, but with the growing of oxide films, diffusion process played an important role increasingly, and became the control factor for continue oxidizing. Then, one or multiple kinds of alloy elements oxide precipitated on the surface, and formed inner spinel oxide of NiCr2O4, CoCr2O4 and Fe(Cr,Al)2O4. During the high temperature oxidation process, N2 will react with Al to generate AlN particles. The further oxidizing has made AlN particles oxidized again and N2 escaped. Finally, the holes with the AlN particles shape have appeared