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Co-based alloys are promising to offer high-temperature corrosion resistance under extreme environmental conditions. Here, we report a novel approach that exploits the characteristics of the oxidation scale by making the specimens ground at three different levels to compare the effects of surface roughness in the presence and absence of external pressure. At a constant pressure of 2.5 MPa, the influence of surface roughness on the oxidation behaviour at an elevated temperature of 1050°C for 430 h has been investigated via scanning electron microscopy coupled with an energy-dispersive X-ray spectrometer and X-ray diffraction. The results have revealed that for rough surfaces the thickness of the oxide scale with Ra = 76.0 nm is significantly higher compared to a smooth surface with Ra = 13.0 nm. Furthermore, the oxide scale on the rough surface has some micro defects and protrusion compared to smooth surfaces. Besides that, under the applied external pressure and surface roughness, more pressure- and roughness-induced cracks and discontinuity have been observed on the oxide scale. [ABSTRACT FROM AUTHOR]