Microstructural Evolution of Oxidation Film on a Single Crystal Nickel-Based Superalloy at 980 A°C

The isothermal oxidation behavior of a single crystal nickel-based superalloy was investigated at 980 A degrees C through XRD, SEM/EDX and EPMA. The mass gain process exhibited two periods: an initial stage followed by a steady-state stage. Based on the experimental results, the rapid formation of alumina and NiO was responsible for the initial stage of mass gain, and the formation of complex spinels phases may dramatically effect on the steady stage. The microstructure of oxidation film, from the top surface down to the base material, was clarified as Ni-rich oxides, Ni-Cr oxides, Cr-Ta-Co oxides, Ni-Al oxides and finally a continuous Al2O3. In addition, AlN formed in the gamma'-free zone. The effect of oxidation film evolution on the oxidation kinetics and mechanism were discussed.