Microstructural evolution and strengthening mechanisms of FGH4095 superalloys with high strength and ductility via hot oscillatory pressing

The high strength and ductility FGH4095 superalloys were prepared by hot oscillatory pressing and heat treatment. The as-sintered superalloy exhibited an average grain size of 8.8 μm in the axial direction and 9.8 μm in the lateral direction. After heat treatment, the grain size became isotropic at approximately 8.2 μm, accompanied by a marked reduction in the proportion of low-angle grain boundaries. Heat treatment also led to isotropic microstructure and hardness, reduced the size and amount of primary γ′, refined secondary and tertiary γ′, and suppressed prior particle boundaries. The heat-treated FGH4095 superalloys exhibited room-temperature tensile strength of 1676 MPa, yield strength of 1286 MPa, and elongation of 17.4%; at 650 °C, the corresponding values were 1449 MPa, 1131 MPa and 16.3%, respectively. The FGH4095 superalloys prepared by this method achieved the strength level of the combined process of hot isostatic pressing, extrusion and isothermal forging, together with superior ductility. The superalloy exhibited a typical microvoid coalescence fracture mode at both room temperature and 650 °C. Synergistic effects of grain boundary strengthening, solid solution strengthening, and multimodal-sized γ′ precipitate strengthening, together with the precipitation of nanoscale carbide phases and stacking faults, enhanced the yield strength and plasticity. Hot oscillatory pressing could effectively shorten the production process of powder metallurgy superalloys and reduce manufacturing costs.