Effects of Al and Ta on the high temperature oxidation of Ni-based superalloys

The effects of Al and Ta on the high temperature oxidation of Ni-8Cr-9.5Co-2.5Mo-6W-(4-5)Al-2Ti-(3-6)Ta-0.1C-0.01B (wt.%) superalloys were examined at 850 °C and 1000 °C by cyclic oxidation tests. The oxidation resistance of the superalloys was improved with an increase in the Al content in the alloy at both temperatures, although the degree of this influence was dependent on Ta concentration at 850 °C. Ta was found to be detrimental to formation of a continuous Al2O3 layer at 850 °C, but it reduced oxidation rate at 1000 °C or when its concentration is over 5 wt.% at 850 °C.