In Situ Observation of Initial Oxidation in Different Generations of Nickel-Based Single-Crystal Superalloys

Due to the application of thermal barrier coatingsThermal barrier coating, the concentrations of Cr in turbine bladeTurbine blades alloys have been limited to low values (approximately 5 at.% or less) since the introduction of second-generation single-crystal superalloysSingle-crystal superalloys. Thermal oxidationOxidation-induced rumpling and swelling of coatingCoating could lead to coatingCoating spallation and inner alloy failure, especially in advanced thin-wall turbine bladesTurbine blades. The initial oxidized surface morphologies and elemental distributions were considered crucial to understanding the failure of superalloysSuperalloys. In this work, initial oxidationOxidation behavior in typical 1st- to 3rd-generation single-crystalSingle-crystal superalloysSuperalloys was systematically studied in situIn situ at nanoscale using an environmental transmission electron microscope from 20 to 800 ℃. With increasing oxygen pressure, the oxide nucleated at the γ/γ’ interface, expanded along the γ channel, and grew into the γ’ phase. In thin foil samples, oxidationOxidation prompted the diffusionDiffusion of base elements from the inner γ and γʹ phases to the γ/γʹ interfacesΓ/γʹ interface in all alloys. With increasing Re content, the oxidationOxidation resistance decreased due to the evaporation of Re2O7 at the γ/γʹ interfaceΓ/γʹ interface in the 3rd-generation superalloySuperalloys. This study provided technical guidance for optimizing the compositions of advanced single-crystalSingle-crystal superalloysSuperalloys to enhance their oxidationOxidation resistance.