No abstract

The oxidation behavior of a cast polycrystalline Ni-base superalloy was studied at 900 and 1000°C and analyzed by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and SEM. The results indicate that the cast Ni-base superalloy exhibits subparabolic oxidation kinetics, which are controlled by the growth of the inner Al-rich layer. A mixed scale forms on the alloy after prolonged oxidation. The oxide scale formed on the c matrix is composed of an outer layer of spinel and a uniform inner, compact Al-rich layer. The oxidation behavior on the region overlying MC carbide precipitates is slightly different from that in the c matrix. The difference is explained by the big difference in composition between MC carbide and c matrix.