High temperature oxidation behaviour of polycrystalline and single crystal Ta stabilized γ'-strengthened Co-Ni-Al-Ta-Cr alloys

Isothermal oxidation was carried out on the polycrystalline and single crystal γ'-strengthened Co-Ni-Al-Ta-Cr alloys at 800–1000 ℃. The oxidation kinetic of both alloys follows logarithmic, cubic and parabolic law at 800 ℃, 900 ℃ and 1000 ℃, respectively. The polycrystalline alloy exhibits superior oxidation resistance at 800–1000 ℃, which can be explained by the effects of grain boundary. Grain boundary diffusion enhances the formation of the protective spinel oxides layer at 800–900 ℃. The beneficial effect of the grain boundary on the spallation resistance of oxides results that the polycrystalline alloy maintains better oxidation properties at 1000 ℃.