Oxidation of a Co-base Superalloy

The oxidation behavior of a cast polycrystalline Co-base superalloy was studied at temperatures from 900 to 1050℃ and analyzed by thermogravimetric analysis (TGA),X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results indicate that a cast Co-base superalloy follows the subparabolic oxidation kinetics at 900 and 1000℃,which are controlled by the growth of the inner Cr-rich layer,and that after oxidation at 1050℃ for 200 h,it almost exhibits the linear oxidation kinetics possible due to the volatility of Cr-rich oxide.A mixed scale forms on the alloy after prolonged oxidation.The oxide scale formed at 900 and 1000℃ is composed of an outer layer of spinel and an inner continuous Cr-rich layer and at 1050℃ is composed of a very discontinuous Cr-rich layer.