High-temperature oxidation of reactively processed nickel aluminide intermetallics

Abstract

A detailed study of the high-temperature oxidation behavior of powder processed Ni 3Al (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/cm 2) 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 Ni 3Al alloys processed using RE showed superior high-temperature oxidation resistance compared to either RP or CS-Ni 3Al at both 1000 and 1200 °C. The oxide scales resulting from the high-temperature oxidation of Ni 3Al consisted of an internal layer of Al 2O 3 (major phase in the case of RE and RP), intermediate layer of NiAl 2O 4, and an external scale of NiO (major phase in the case of CS-Ni 3Al 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-Ni 3Al and RE-Ni 3Al in air after 400 h.