Improving the mechanical properties of a novel nickel-based superalloy via the cubic secondary γ′ and the regulation of tertiary γ′

The heat treatments significantly impact the mechanical properties and performance of the nickel-based powder superalloys. This study investigates the effect of heat treatments on the precipitation behavior of the γ′ phase and the mechanical properties of a novel nickel-based powder superalloy. By altering the solution treatment temperatures, holding times, cooling rates, and applying a two-step aging, the effect of heat treatments on the morphologies, volume fractions, and sizes of the γ′ phase were clarified. The mechanical properties after different heat treatments were evaluated by Vickers hardness tests and tensile tests at room temperature. As the cooling rates decreased, the volume fractions and sizes of the secondary γ′ phase significantly increased, and the morphology of the γ′ evolved from the spherical to the cubic, eventually forming the dendritic shape. The heat treatments involving solution treatment (1150 °C/2 h, air cooling/AC) and two-steps aging (870 °C/8 h, AC + 760 °C/16 h, AC) resulted in improving of the alloys mechanical properties, with tensile strength, yield strength, elongation and Vickers hardness reaching 1470 MPa, 1138 MPa, 11.87 %, and 458 Hv, respectively. The results indicate that the higher the cubicity of secondary γ′ phase, the higher the dislocation density, and the more pronounced the dislocation cutting effect. With sizes of the tertiary γ′ increasing, the deformation mechanism shifts from weakly coupled dislocation cut to strongly coupled cut. The combined effects of the cubic secondary γ′ and the deformation mechanisms transforming of the tertiary γ′ improve the mechanical properties of the alloys.