Effects of temperature and Ti addition on high-temperature oxidation behaviors of Co-Al-W based superalloys

Abstract

PurposeDue to the special service environment of superalloys, this paper aims to obtain effects of temperature and Ti addition on high temperature oxidation behavior of Co-Al-W-B alloys.Design/methodology/approachIsothermal oxidation experiment of Co-Al-W-based alloys were carried out at 800°C, 900°C and 1000°C for different times (3, 5, 10, 20, 50 and 100 h) referring to the method of HB5258-2000. Oxidation weight gain curves and oxidation products were detected.FindingsThe results showed that the average oxidation rates of Co-Al-W-B alloy at 800 °C and 900 °C were 0.489 g·m−2·h−1and 0.888 g·m−2·h−1, respectively, which belonged to an antioxidant grade. However, the average oxidation rate at 1000 °C was 2.068 g m−2·h−1, belonging to the secondary oxidation resistance class. In the alloy with Ti addition, dense Ti oxides film were formed at the early oxidation stage and then gradually diffused later, which can increase the oxidation resistance of the alloys to some extent. By analyzing the oxidation products of Co-Al-W-B alloy, it was found that a dense Al2O3layer could be formed when the alloy was oxidized at 800°C. The continuous Al2O3layer would prevent the oxygen from further spreading and make the alloy into the stable oxidation stage. However, only a non-dense Al2O3layer were observed with 900°C oxidation.Originality/valueIt can provide references for the composition design, preparation process optimization and protective coating selection of the γ′ phase strengthened cobalt-base superalloys.