AlCrFeNi3共晶中熵合金的高温氧化行为

High Temperature Oxidation Behavior of AlCrFeNi3 Eutectic Medium Entropy Alloy

摘要:

为开发具有优异抗高温氧化性能的AlCrFeNi₃共晶中熵合金，探究其氧化层组织演变与氧化机理显得尤为重要。通过真空中频感应熔炼炉制备AlCrFeNi₃共晶中熵合金，在800 ℃下进行氧化增重试验，测定该合金的高温抗氧化性能。利用X射线衍射仪表征氧化膜的物相组成，使用扫描电镜表征高温氧化后的氧化膜表面、氧化层截面微观组织演变，并结合EDS能谱仪分析元素分布，以研究合金的高温氧化行为。结果表明，AlCrFeNi₃共晶中熵合金在800 ℃下单位面积氧化增重与氧化时间的关系符合抛物线规律，抛物线速率常数为0.007 13 g²?m^-4·h^-1，抗氧化性属于完全抗氧化级。AlCrFeNi₃共晶中熵合金在800 ℃下氧化产物主要为Cr₂O₃和Al₂O₃，氧化100 h后合金表面膜平整光滑并未出现裂纹与氧化剥落，只在合金氧化表面形成了密集分布的深黑色Al₂O₃和少量浅灰色岛状Cr₂O₃，膜厚度约为2.504 μm。氧化初期，基体表面附近O₂充足，氧化反应主要由界面反应控制，Al优先与O₂发生反应生成Al₂O₃；随着氧化的继续，Al、Cr离子向外扩散产生阴极反应，氧离子向内扩散发生阳极反应使氧化物增加；稳定氧化期，合金基体和氧化膜紧密贴合，氧化膜具有良好的保护性和完整性，最终形成致密Al₂O₃与少量Cr₂O₃的混合氧化层。揭示AlCrFeNi₃共晶中熵合金的抗高温氧化机理，对促进高性能中/高熵合金的发展和工程应用具有一定的理论意义。(专精特新·特殊环境材料服役行为专辑十五之五)

Abstract:

AlCrFeNi₃ eutectic medium entropy alloy with excellent high temperature oxidation resistance was developed， and the microstructure evolution and oxidation mechanism of its oxide layer were investigated. AlCrFeNi₃ eutectic medium entropy alloy was prepared by vacuum medium frequency induction melting furnace. The oxidation weight gain test was carried out at 800 ℃， determing the high temperature oxidation resistance. The phase composition of the oxide films was characterized by X-ray diffraction. The microstructure evolution of the surface of the oxide films and the cross section of the oxide layer after high temperature oxidation were characterized by scanning electron microscopy， and the element distribution was analyzed by EDS. The high temperature oxidation behavior of the alloy was investigated. The results show that the relationship between the oxidation weight gain per unit area and the oxidation time of AlCrFeNi₃ eutectic medium entropy alloy at 800 ℃ conforms to the parabolic law. The parabolic rate constant is 0.007 13 g²·m^-4·h^-1， indicating complete oxidation resistance. The oxidation products of AlCrFeNi₃ eutectic medium entropy alloy at 800 ℃ are mainly Al₂O₃ and Cr₂O₃. After oxidation for 100 h， the surface film is smooth without cracks and oxidation spalling. Densely distributed dark black Al₂O₃ and a small amount of light gray island Cr₂O₃ are formed on the oxidation surface of the alloy， with a thickness of about 2.504 μm. In the initial stage of oxidation， O₂ is sufficient near the surface of the matrix. The oxidation reaction is mainly controlled by the interface reaction promoting preferential Al oxidation to form Al?O?. With the progress of oxidation， Al and Cr ions diffuse outward to produce cathode reaction， while oxygen ions diffuse inward to produce anode reaction， resulting in the formation of increased oxides. During the stable oxidation period， the alloy substrate and the oxide film are closely bonded， forming the oxide film with good protection and integrity. The alloy finally forms a mixed oxide layer of dense Al₂O₃ and a small amount of Cr₂O₃. This study reveals the high temperature oxidation resistance mechanism of AlCrFeNi₃ eutectic medium entropy alloy， which has certain theoretical significance for promoting the development and engineering application of high performance medium/high entropy alloys.