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

Isothermal oxidation was carried out on the polycrystalline and single crystal gamma'-strengthened Co-Ni-Al-Ta-Cr alloys at 800-1000 degree celsius. The oxidation kinetic of both alloys follows logarithmic, cubic and parabolic law at 800 degree celsius, 900 degree celsius and 1000 degree celsius, respectively. The polycrystalline alloy exhibits superior oxidation resistance at 800-1000 degree celsius, 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 degree celsius. The beneficial effect of the grain boundary on the spallation resistance of oxides results that the polycrystalline alloy maintains better oxidation properties at 1000 degree celsius.