In Situ Oxidation in Ni-Based Single-Crystal Superalloys with Varying Re Contents Observed by Environmental Transmission Electron Microscopy

In situ environmental transmission electron microscopy has previously been applied to traditional alloys and has been verified as a powerful tool for studying oxidation mechanisms. Single-crystal Ni-based superalloys are often used for commercial turbine blades, especially 1st- to 3rd-generation superalloys. The reactivity to oxidation of the single-crystal Ni-based superalloys was the main factor in deciding their bulk oxidation resistance. An overall study on different generations of various Re-containing Ni-based superalloys was conducted in this study to compare their difference in oxidation properties using an in situ technique. Nanoscale structural and elemental distributions across the γ/γ′ interface were assessed on three typical 1st- to 3rd-generation superalloys via modern electron microscopy. Oxidation at the γ/γ′ interface was systematically analysed by an in situ oxidation process in an environmental transmission electron microscope to reveal the nanoscale oxidation mechanisms and the roles of key elements. Preferential oxidation of the γ/γ′ interface is revealed in oxidation mechanisms. Aggregation of Cr and Re in the γ/γ′ interfaces of the 0Re and 7Re alloys induced a larger lattice misfit and a corresponding stress, which prompted priority oxidation at the interface. Key factors, including alloy elements and microstructures, are extracted, and this technique is expected to be applicable to more materials.