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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]

DZ40M alloy is a new Co-base superalloy, which is suitable for the blade material of gas turbines. In this paper, isothermal oxidation of an aluminide coating on this alloy was examined at 900–1100°C in air. It was observed that the weight gain at lower temperatures (900 and 1000°C) was greater than that at the higher temperature (1050°C), which was due to the formation of both θ-Al2O3 and α-Al2O3 at 900 and 1000°C but only α-Al2O3 at 1050 and 1100°C. [ABSTRACT FROM AUTHOR]

• The activation energy of oxidation can be from the kinetic data of weight gain. • The oxidation reaction rate can be further expressed from the activation energy. • This expression can be favorable for knowing the oxidation behavior of superalloys. This presentation deals with the activation energy of oxidation for a practical Co-base superalloy suitable for turbine blades. The kinetic data of weight gain were measured to get the corresponding rate constants of oxidation for this high temperature alloy oxidized at 900 °C and 1000 °C in air, and the activation energy of oxidation has been derived for this alloy at high temperatures of 900~1000 °C. According to this, the specified relations can be further achieved to express the oxidation reaction rate for this superalloy at different temperatures in air. These would be favourable for knowing the oxidation behaviour of the superalloy at high temperatures in air, and evaluating the service life to get the safe application for the superalloy. [ABSTRACT FROM AUTHOR]