Role of volatilization of molybdenum oxides during the cyclic oxidation of high-Mo containing Ni-based single crystal superalloys

Highlights: •The volatilization of refractory metal oxides may influence the mass changes during the transient oxidation in the high refractory elements-containing single crystal superalloys. •The spallation of the oxide scales determines the mass change of the samples during the steady oxidation in the cyclic oxidation test. •Thicker oxide scales show stronger tendency to spallation owing to the higher elastic strain energy. •Finite element calculations show the stress distributions of the oxidation systems in the Ni-based single crystal superalloy. -- Abstract: The cyclic oxidation behavior of two high-Mo containing Ni-based single crystal superalloys with different Al contents at 1100 °C has been investigated. The higher formation tendency of the continuous and dense α-Al₂O₃ scales in the alloy with higher Al content can prevent the volatilization of MoO₃ through decreasing the diffusion of Mo. Besides the spallation of oxide scales, the volatilization of refractory metal oxides can also result in the mass loss of the samples in the cyclic oxidation tests, especially in the Ni-based single crystal superalloys with high contents of refractory elements and weak formation tendency of continuous α-Al₂O₃ scales.