The oxidation resistance of FGH4097, FGH4099, and a new Ni-based powder metallurgy (PM) superalloy FGHXX at 750-1100 ℃ is investigated by isothermal oxidation tests on the basis of FGH4095 and FGH4096 superalloys. Results show that the oxide layer of FGH4097 superalloy, mainly consist of Al₂O₃, become denser modestly with temperature rising without internal oxidation. Even after heating at 1100 ℃ for 200 h, the oxide layer is approximately only 10 μm. While the thickness of FGH4099 and FGHXX increase with temperature rising, but decrease at 1100 ℃ because of the oxide layer spallation. The surface of FGH4099 and FGHXX become layered above 900 ℃, which the inner side of both superalloys is Al₂O₃, and the outer side of FGH4099 superalloy is mainly Cr₂O₃, TiO₂, Ta₂O₅, and Nb₂O₅, and that of FGHXX is mainly Cr₂O₃, TiO₂, and Ta₂O₅ at 900 ℃ and 1000 ℃. While the outer side of both superalloys is comprised of (Ni, Co)Cr₂O₄ and Cr₂O₃ at 1100 ℃. The difference of oxide layer constitution and morphology comes from Al content discrepancy in five Ni-based PM superalloys. Therefore, the oxidation resistance from highest to lowest of the above five Ni-based PM superalloys is FGH4097>FGHXX≈FGH4099>FGH4095>FGH4096, which lays the theoretical and practical foundation to the material selection of components such as aero-engine turbine discs.

Heat treatment is the most critical thermal process determining the properties of powder metallurgy（PM）superalloy components, with FGH96 currently being one of the most prevalent PM Ni-based superalloys. This work investigates the effects of two distinct solution heat treatment cooling methods—full air cooling quenching and combined air-oil cooling quenching—on the microstructure and properties of FGH96 alloy ring parts. The results indicate that both cooling methods yield equivalent grain sizes, ranging from grade 6.5 to 7. Notably, full air-cooled rings exhibit more homogeneous distribution of secondary γʹ phase. In contrast, rings subjected to combined air-oil cooling exhibit coarser secondary γʹ phases, with reduced quantity on the inner side compared to the outer side, attributable to internally diminished cooling rate. During the later stage of quenching, ring parts undergoing full air cooling experience a slower cooling rate than those using combined air-oil cooling. Furthermore, fine γʹ phases, possessing sizes between the secondary and tertiary γʹ phases, precipitate along the grain boundaries using full air cooling method, leading to grain boundary strengthening. This enhances tensile strength but reduces elongation and plastic elongation at 68 h in high-temperature creep tests. Additionally, due to the more uniform cooling rate throughout the ring during full air cooling quenching, the surface residual stress reduces with more uniform distribution, thereby augmenting dimensional stability during subsequent machining processes.