Oxidation resistance of three Ni-based powder metallurgy superalloys

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.