The γ-γ′ Co-based superalloys have begun to be extensively studied due to their promising properties and capability for creating beneficial microstructure. The interest of researchers from around the world is mainly due to high operating temperature and mechanical properties, which are much higher compared to that of conventional cobalt superalloys reinforced with carbides. The works related to the development of this group of materials are focused on increasing the operating temperature, mechanical properties and oxidation resistance, which is much lower compared to that of nickel-based superalloys. One way of influencing the properties is addition of reactive elements (RE), namely yttrium. In this study, the influence of this element on the high-temperature oxidation resistance of cobalt superalloys from the Co-Ni-Al-W group was investigated.

Therefore, The Co-9Al-9W, Co-9Al-9W-0.5Y, Co-20Ni-9Al-9W-0.5Y (at.%) alloys were prepared via VIM technique. The alloys were subjected to isothermal and cyclic oxidation at 900 °C for 500 h. Furthermore, the oxide scales were analyzed by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

The Y-containing alloys exhibit lower oxidation rate compared to that of Co-9Al-9W. Moreover, Y improved cyclic oxidation resistance, especially in the case of the alloy containing nickel. The improved oxidation resistance may be caused by formation of Y rich oxides within the scale and at the metal-oxide interface. Depending on the depth of the oxide layer, Y-rich phases oxidized and formed Y2O3 or Y2WO6 phases.

This work was supported by National Science Centre (Project 2018/29/N/ST8/02062).