Effect of Re on microstructure and mechanical properties of γ/γʹ Co-Ti-based superalloys

Three compositions of Re containing Co-Ti-based alloys with γ/γ′ two-phase microstructure were obtained based on the determined phase relationship in the Co-rich corner at 800 °C. The effect of Re on microstructure, elemental partition behavior, thermodynamic properties, lattice parameter misfits, mechanical properties and γ′ coarsening behavior of the Co-Ti-Re alloys were investigated. The γ/γ′ lattice parameter misfit of the alloys decreases from 0.72% to 0.50%, and the γ′ coarsening rate constant K of alloys decreases from 0.30 × 10⁻²⁷ m³ s⁻¹ to 0.073 × 10⁻²⁷ m³ s⁻¹ as Re content increasing form 1 at. % to 5 at. %. Additionally, the volume fraction of γ′ phase (V_γ′) increases from 42.15% to 53.19% and the γ′ solvus temperature increases from 1059 °C to 1085 °C (T_solvus-γ′) with increasing Re content. Moreover, the 0.2% flow stresses and the 0.2% specific flow stresses of all three alloys exhibit negative temperature dependence at the temperatures ranging from room temperature to 900 °C. And both the 0.2% flow stresses and the 0.2% specific flow stresses increase with the Re content.