The Effect of Yttrium on Oxide Scale Growth on Co-Al-W-based Superalloys

The study on the individual role of yttrium (Y) and Y-related phases during scale formation on Co-9Al-9 W (at%) and other Co-based alloys during isothermal and cyclic oxidation at 900 degrees C was performed. The addition of Y increased the oxidation resistance of Co-(Ni)-Al-W alloys, especially under cyclic conditions due to an oxide keying effect related to the internal oxidation of Y-containing phase constituents. The Y-containing oxide areas corresponded in number, size, shape, and spatial distribution to the original Y-rich particles in the alloy. The mechanism describing the formation of Y-related oxides within the oxide scale was proposed.