Effects of Ta and Ti content on microstructure and properties of multicomponent Co–Ni-based superalloys

Abstract

The content and the existing form of refractory elements significantly affect the performance in service of superalloys, which has gained extensive attention in this field. In this study, basic influence rule of diverse Ta and Ti contents on the microstructure and properties of the novel γ′ phase strengthened Co–Ni-based superalloys is clarified by thermodynamic calculation and experimental research. Under the premise of a total Ta and Ti content of 5 at%, increasing Ta content elevates the solvus temperature of γ′ phase and volume fraction of Laves phase, and also reduces the volume fraction of β phase in the as-cast alloys. Moreover, the average size of γ′ phase goes down and the coarsening of γ′ phase is inhibited simultaneously in the alloy after aging treatment. Consequently, increasing the content of Ta can enhance the microstructure stability and elevates the Vickers hardness and yield strength of the alloy. However, the density and cost of the alloy have to be raised. Meanwhile, the variation of Ta and Ti contents affects the oxidation performance of the alloys by influence the volatilization of W and Mo oxides. 2Ta3Ti and 3Ta2Ti alloys possess favorable oxidation resistance at 1050 °C. Considering the effect of Ta and Ti elements and normal performance requirements of Ni-based superalloys, 3Ta2Ti alloy has more impressive engineering application prospects. This work provides a solid foundation for optimizing the composition and improving the properties of Co–Ni-based superalloys.