High-temperature characterization of reactively processed nanostructure nickel aluminide intermetallics

A detailed study of the high-temperature oxidation behavior of reactively powder processed nanostructure nickel aluminides Ni3Al and NiAl (with and without microalloying additions) starting from elemental nanopowders in air at two different temperatures (800 and 1000 °C) for 200 h was carried out, as well as the sulphidation behavior (in 10% SO2, 90% He atmosphere) at 800 °C for 100 h. The weight gain per unit area (mg/cm2) due to oxide scale formation at a given exposure time t (h) and temperature was discussed. Thermodynamics and kinetics were used to explain the oxidation mechanism.The high temperature oxidation/or sulphidation resistance was improved due to nanostructure grains formation. Also, additions of a small amount of Nb (up to 4 wt%) as microalloying element resulted in a significant increase in the high temperature oxidation/ or sulphidation resistance compared to the microalloying free intermetallics. Also, the results indicated that nanostructure NiAl (with and without micro-alloying elements) showed superior high temperature oxidation/or sulphidation resistance compared to the nanostructure Ni3Al (with and without micro-alloying elements). Both XRD and SEM/EDS-analysis were used to identify the oxide phases present after the high temperature oxidation/or sulphidation exposure of nanostructure aluminides at 1000 °C after 200 h, and at 800 °C after 100 h, respectively.