Effect of Heat Treatment on Microstructure and Mechanical Properties of a Novel Co-based Superalloy

In this work, the microstructure and mechanical properties of a novel Co-based supersuperalloy reinforced by the γ′ phase will be investigated after and before heat treatment. The results show that the Co–25Ni–20Cr–8Mo–3Ti–1Al–1Nb superalloy, solution at 1045 °C for 6 h solid and aging at 660 °C for 4 h aging conditions has excellent strength and plasticity. The ultimate strength is 1065 MPa at 25 °C, with an elongation of 62%, which is mainly due to the uniform and fine grain organization and the large number of nano-size γ′ phases within the grains. The yield strength of the superalloy reaches 423 MPa at 600 °C, which is lower than that of 650 MPa at 25 °C, because the failure mode of the superalloy changes from perforation failure at 25 °C to a long-crystal fracture at high temperature. Meanwhile, the grain boundaries under high-temperature stress would become weak zones that promote the formation and propagation of cracks. In addition, the carbides at the grain boundaries are relatively reduced after heat treatment, which can also effectively improve the strength and plasticity of the superalloy.