Cyclic oxidation behavior of Ni3Al-basedsuperalloy.

Cyclic oxidation behavior of a polycrystalline Ni 3 Al-based superalloy under as-cast and solution treated conditions was investigated in detail. SEM equipped with energy dispersive X-ray spectrometer and high-resolution transmission electron microscopy was used for microstructure observation and mechanism analysis. Results showed that oxidation process occurred along eutectic area (γ-γ′) and dual phase area (γ+γ′)interfaces firstly for as-cast alloy and oxide scales along (γ-γ′)/(γ+γ′) interfaces spalled gradually with oxidation process proceeding. As for the solution treated alloy, though oxidation process also occurred along (γ-γ′)/(γ+γ′) interfaces, no obvious spalling of oxide scales was observed under the present conditions. Due to the precipitation of Hf-containing carbides which can increase the adhesion of scales and its segregation to Al 2 O 3 grain boundaries during cyclic oxidation to hinder outward migration of Al, leading to slower growth rate of scales. During the long-time (8–200 h) cyclic oxidation process of the solution treated alloy, O atoms continuously diffused towards the matrix along the pores in scales, resulting in thickening of Al 2 O 3 layer. Moreover, thickening of Al 2 O 3 layer also hindered the outward diffusion of Ni and a small amount of NiO was observed on surface of specimen after long-term cyclic oxidation, meaning the improvement of oxidation resistance. • The oxidation behavior occurs on the interface area firstly. • Hf-containing carbides increase the adhesion force of scale. • Solution elements and thermal expansion affect the oxidation behavior. [ABSTRACT FROM AUTHOR]