Oxidation Behavior of γ′-Ni3Al-Based Ni–20Al–5Cr Alloys With and Without Reactive Elements Under Different Heating Conditions

High-temperature oxidation of a model γ′-Ni3Al-based Ni–20Al–5Cr alloy and versions of this alloy doped with Y, Hf, or Si, or some combination of these, was investigated. Oxide scale evolution was characterized using SEM, TEM, and TOF–SIMS. The resulting scale microstructures depended quite sensitively on the heating rate to the oxidation temperature of 1100 °C. However, whatever the heating rate, the dopant additions improved the oxidation resistance of the base alloy. The reactive elements Y and Hf, if segregated to the surface during preheating under conditions where appreciable oxidation was not possible, suppressed transient oxidation and facilitated the exclusive growth of the thermodynamically stable α-Al2O3 scale.