Isothermal Oxidation Behavior of Nickel-based Superalloy U720Li in Different Oxidation Stages at 750℃
The increasing service temperature of aero-engine turbine discs makes more stringent requirements for oxidation resistance of the materials.U720Li alloy is a high-strength nickel-based superalloy for turbine discs with a long-term ser-vice temperature up to 750℃.Clarifying the oxidation behavior at service temperatures of this alloy is of great significance for improving the service life of high-performance turbine discs.In this paper,the oxidation kinetics curve of forged U720Li alloy at 750℃has been determined by the static weight gain method,and the oxide film morphology,structure and element distribution in different oxidation stages were analyzed by XRD and SEM-EDS.The results show that the U720Li alloy has excellent oxidation resistance at its service temperature,and its isothermal oxidation kinetic curve at 750℃basically follows the cubic law,reaching the full anti-oxidant level.It has been analyzed that the loose γ-Cr2O3 is generated at the early oxidation stage of U720Li alloy.The γ-Cr2O3 layer spalls continuously as the oxidation proceeds,and the oxide film becomes more continuous and dense and forms a complex multilayer structure.Meanwhile,a γ´ de-pleted layer is gradually formed within the matrix nearby the oxide film.In the stable oxidation stage,the oxide film be-comes more continuous and dense,forming a regular double-layer structure which includes the dense α-Cr2O3 outer layer and α-Al2O3 inner layer.The formation of continuous dense α-Cr2O3 and α-Al2O3 layers can effectively prevent the internal diffusion of oxygen and external diffusion of alloying elements,which guarantees the excellent oxidation resistance of U720Li alloy.
U720Li AlloyOxidation BehaviorOxide Filmγ´ Depleted LayerService Temperature
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万方数据
维普
