Microstructural Stability and Mechanical Properties of a Novel Weldable Ni-based Superalloy during Thermal Exposure at 800 °C

The microstructural evolution, stress rupture life, tensile properties, and deformation behavior of a novel weldable Ni-based superalloy destined for cast components of aero engines were investigated during prolonged isothermal exposure at 800 °C. The size of γ′ particles increased from ~ 30 to ~ 190 nm and exhibited a coarsening rate of 113 nm³/h after 8000 h of aging, which is significantly lower than that of other conventional nickel-based superalloys, such as C263 and IN718 plus. Its high-temperature tensile properties showed by a slight decrement with increased aging time. Stress rupture life, under conditions of 815 °C/379 MPa, declined as exposure time was prolonged. These characteristics in mechanical properties are mainly attributed to the coarsening of γ′ particles. The connected M₂₃C₆, the decomposition of MC with the reaction of MC + γ  → M₂₃C₆ + γ′ and the precipitation of η phase also have detrimental effect. These microstructural transformations led to the change of the deformation mechanism. Initially, the deformation mechanism involved Orawan mechanism and the activation of multiple stacking faults. However, in the thermally aged state, it shifted to dislocation shearing mechanism. In addition, microcracks were prone to initiate and propagate near voids created by MC decomposition and M₂₃C₆ carbide coarsening, potentially inducing premature fracture failure in the alloy.