On oxide formation on a single crystalline Ni-based superalloy at 900 C in SO₂ containing atmosphere: The effect of surface treatment

The oxidation behavior of the single crystalline SCA425+ (17Cr-10Al-3Ta-Ni bal.) after two different surface finish procedures (grinding and polishing) was investigated after cyclic exposures at 900 degrees C in SO2 containing atmosphere up to 260 h. The microstructure and chemistry of the produced oxide scales were studied using highresolution methods, SEM/EDX, TEM, and STEM. The investigation revealed that grinding provides more effective diffusion paths, so that the material is able to form a protective continuous alumina layer, while an extensive internal oxidation takes place on the polished sample. In addition, a numerical model, based on the cellular automata approach, was developed and used to consider the effect of dislocation pipe diffusion in combination with diffusion processes and oxide formation. Good agreement between the model and experimental results was obtained.