Abstract Microstructural evolution and isothermal oxidation behavior of a cast Ni-based superalloy have been investigated at 800 °C, 900 °C and 1000 °C in air. Results show that the oxidation kinetics of the Ni-based superalloy follows parabolic law at elevated temperatures. Oxide scales after oxidation can be divided into external layer, continuous Cr2O3 layer linked with internal TiO2, discontinuous Al2O3 layer and γ′-depletion zone. Due to the segregation of alloying elements, densely granular zone and porous zone are formed at 800 °C. External oxide layer is a mixed oxides zone, which mainly consists of TiO2 and Cr2O3 at 800 °C and 900 °C, NiO and NiCr2O4 at 1000 °C. The formation condition of NiO and NiCr2O4 is mainly after 50 h oxidized at 1000 °C. Thickness growth rate of Cr2O3 and Al2O3 layers decrease gradually during oxidation process, indicating that external oxides can effectively prevent the inward diffusion of oxygen. The oxidation activation energy of the experimental Ni-based superalloy is confirmed to be 205.3 kJ mol−1 and the oxidation process is controlled by diffusion of oxygen, Ti and Cr ions.

中文翻译：

---

镍基高温合金暴露在空气中的微观结构演变和氧化行为

摘要 研究了铸造镍基高温合金在 800 °C、900 °C 和 1000 °C 空气中的显微组织演变和等温氧化行为。结果表明，镍基高温合金在高温下的氧化动力学遵循抛物线规律。氧化后的氧化皮可分为外层、与内部TiO2相连的连续Cr2O3层、不连续Al2O3层和γ'-耗尽区。由于合金元素的偏析，在800℃时形成致密颗粒区和多孔区。外部氧化层为混合氧化物区，主要由800℃和900℃的TiO2和Cr2O3，1000℃的NiO和NiCr2O4组成。NiO和NiCr2O4的形成条件主要是在1000℃氧化50h后。Cr2O3 和 Al2O3 层的厚度生长速率在氧化过程中逐渐降低，表明外部氧化物可以有效阻止氧气向内扩散。实验证实镍基高温合金的氧化活化能为 205.3 kJ mol-1，氧化过程受氧、钛和铬离子的扩散控制。