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.
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