A. J. Heidloff, T. Izumi, Iowa State University, Ames, IA; B. Gleeson, University of Pittsburgh, Pittsburgh, PA
Novel heat-treatable γ-Ni+γ'-Ni3Al-based alloys having excellent resistance to both high-temperature oxidation and creep are being developed in a systematic manner using multiple alloying additions, including Pt and Ir, i.e., platinum group metals (PGMs). Alloys possessing such combined high temperature properties could find use in current and future niche aero applications involving extreme conditions. The microstructures, phase equilibria and thermal stabilities of the alloys studied were fully characterized. This included determination of the γ and γ' volume fractions and lattice parameters over the temperature range 700-1300°C using controlled-atmosphere synchrotron radiation. The results were correlated with the alloy microstructures. Alloys subjected to intermediate-temperature creep were investigated using TEM and the resulting dislocation network spacings were used to determine γ/γ' lattice misfits, which were compared to the unstressed measurements obtained from the synchrotron results. Oxidation behavior was studied at 1000°C under both thermal cycling and isothermal conditions. PGM additions were found to reduce the detrimental effects of “strengthening” alloying additions on oxidation and to promote exclusive formation of a continuous Al2O3 scale. Investigation of short-term oxidation behavior was also conducted to determine compositional and microstructural factors affecting the oxide-scale evolution.
Summary: Novel heat-treatable
g-Ni+
g'-Ni
3Al-based alloys having excellent resistance to both high-temperature oxidation and creep are being developed in a systematic manner using multiple alloying additions, including Pt and Ir,
i.e., platinum group metals (PGMs). Alloys possessing such combined high temperature properties could find use in current and future niche aero applications involving extreme conditions.
