Effect of Ti addition on high-temperature oxidation behavior of Co–Ni-based superalloy

The oxidation behavior of a newly designed Co–Ni-based alloy with varied addition of Ti (1.4 and 2.1 wt.%, hereafter referred as 1.4Ti and 2.1Ti alloys) was explored in air at 900 °C. It is found that an outer oxide layer composed of CoO, an intermediate oxide layer composed of intermittent TiO2 plus continuous Cr, W-rich oxides, and an inner oxidized region composed of Al2O3 were formed on the surface of 1.4Ti alloy, whereas the oxide structure of 2.1Ti alloy was composed of CoO as the outer oxide layer, continuous TiO2, Cr2O3, and WO3 as intermediate oxide layer, and Al2O3 as the inner oxidized region. With increasing Ti content, continuous TiO2 films formed in the intermediate oxide layer, which would lead to the formation of compact Cr2O3 and improved oxidation resistance after 100 h oxidation at 900 °C. These observations indicated that Ti addition can improve the high-temperature oxidation resistance of Co–Ni-based alloys.