Influence of Multi-Stage Heat Treatment on Microstructure and Mechanical Properties of a Generic Ni-Based Superalloy

This study investigates the influence of a multi-stage heat-treatment strategy on the microstructural evolution and room-temperature mechanical properties of a generic precipitation-strengthened Ni-based superalloy. The applied heat-treatment sequence consisted of an as-received condition, high-temperature solution treatment at 1090°C, secondary solution treatment at 980°C, and final aging at 760°C for 16 h. Microstructural characterization using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) revealed progressive dissolution of coarse γ′ precipitates, redistribution and stabilization of carbide phases, and the formation of a refined bimodal γ′ precipitate distribution after aging. The aged condition exhibited primary γ′ precipitates with sizes of 35–45 nm and secondary γ′ precipitates of 10–20 nm, which contributed to effective precipitation strengthening. Mechanical testing demonstrated a significant enhancement in hardness and tensile strength following the multi-stage heat treatment. Vickers hardness increased from 235 HV in the as-received condition to 347 HV after final aging. Yield strength and ultimate tensile strength were also markedly improved, with the final aged condition exhibiting yield strengths in the range of 840–1140 MPa and ultimate tensile strengths of 965–1390 MPa, depending on specimen variability. The observed mechanical improvements are attributed primarily to γ′ precipitation strengthening, solid-solution strengthening from alloying elements, and stabilized grain-boundary carbides. These results demonstrate that carefully designed multi-stage heat-treatment schedules can effectively tailor microstructure and enhance mechanical performance, providing useful guidance for the processing and optimization of Ni-based superalloys.