High-temperature oxidation of reactively processed nickel aluminide intermetallics

A detailed study of the high-temperature oxidation behavior of powder processed Ni3Al (combustion synthesized (CS), reactively pressed (RP), and reactively extruded (RE)) in air at two different temperatures (1000 and 1200 °C) for 400 h was carried out. 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 results indicated that Ni3Al alloys processed using RE showed superior high-temperature oxidation resistance compared to either RP or CS-Ni3Al at both 1000 and 1200 °C. The oxide scales resulting from the high-temperature oxidation of Ni3Al consisted of an internal layer of Al2O3 (major phase in the case of RE and RP), intermediate layer of NiAl2O4, and an external scale of NiO (major phase in the case of CS-Ni3Al at 1000 and 1200 °C). Both XRD and SEM/EDS-analysis were used to identify the oxide phases present after the high-temperature oxidation exposure at 1200 °C of CS-Ni3Al and RE-Ni3Al in air after 400 h.