Improvement of isothermal oxidation resistance of a γ′-strengthened Co–Al–W–Mo–Ta–B alloy at 800 °C via doping Ce

Abstract

Isothermal oxidation resistance, oxide scale evolution and failure mechanism of Ce-doped Co–Al–W–Mo–Ta–B alloy (0.01 at%, 0.05 at%, 0.10 at% and 0.20 at% Ce) exposed at 800 °C were compared. The 0.01Ce and 0.05Ce alloys were consisted of γ/γ′ coherent microstructure, while the κ-Co3W compound precipitated at the grain boundary of the 0.10Ce and 0.20Ce alloys in addition to the γ/γ′ microstructure. The oxidation kinetics curves of the Ce-doped alloys exhibited a parabolic time dependence on the weight gain. With an increasing nominal Ce content, the weight gain of the Co–Al–W–Mo–Ta–B alloys monotonically decreased. An oxide scale composed of a dense and uniform outer Co3O4 + CoO layer, a middle CoAl2O4 and CoWO4 compound layer and an inner Al2O3 layer. The excellent oxidation resistance of 0.2Ce alloy was mainly attributed to a shorter incubation stage for the formation of the continuous and protective Al2O3 layer and the thickest Al2O3 layer during entire oxidation process.