The effect of grain boundaries on high temperature oxidation of new γ′-strengthened Co–Al–W–B superalloys

Abstract

Isothermal oxidation in air was carried out on a γ′-strengthened single crystalline Co–Al–W–B superalloy at 800, 900, and 1000°C. The absence of grain boundaries leads to inferior oxidation properties at 800 and 900°C, and improved properties at 1000°C, compared to a polycrystalline alloy of the same composition. At lower temperatures, grain boundary diffusion is dominant and assumed to be the reason for enhanced B-accumulation in the inner oxide layer and enhanced formation of the protective inner Al2O3 layer. However, at 1000°C superior oxidation resistance of the single crystalline superalloy can be observed.