Effect of Cr, Co, and Ti additions on the high-temperature oxidation behavior of Ni3Al

The oxidation behavior of Ni3Al+2.90 wt.% Cr, Ni3Al+3.35 wt.% Co, and Ni3Al+2.99 wt.% Ti alloys was studied in I atm of air at 1000, 1100, and 1200 degrees C. Isothermal tests revealed parabolic kinetics for all three alloys at all temperatures. Cyclic oxidation for 28 two-hour cycles produced little spallation at 1000 degrees C, but caused partial spallation at 1100 degrees C. Especially, at 1200 degrees C severe spallation in all three alloys was observed Although additions of Cr, Co, or Ti to Ni3Al alloys slightly increased the isothermal-oxidation resistance, the additions tended to decrease the cyclic-oxidation resistance. The major difference in the oxidation of the three alloys compared with the oxidation of pure Ni3Al alloys was the existence of small alpha-Al2O3 particles in the middle of the alpha-Al2O3 scale and the formation of irregularly shaped Kirkendall voids at the alloy-scale interface.