The solid solution cooling heat treatment of powder, high-temperature alloys is a crucial part of the process for ensuring the strength of materials during the forging processing. The influence of the γ′ phase and other microstructures in high-temperature alloy forgings on their macroscopic mechanical properties has been confirmed in numerous studies. Among them, the performance of the γ′ phase during the solid solution cooling process varies significantly depending on the cooling rate. This study uses the FGH99 nickel-based high-temperature alloy as the research material. It examines the precipitation and microstructure evolution law of the material under different cooling rates and its impact on the macroscopic mechanical properties of the material. Additionally, a prediction model of the organizational properties based on the cooling rate is constructed. The research findings indicate that there is a distinct positive correlation between the yield strength of the material and the cooling rate. As the cooling rate increases, the yield strength rises from 910.8 MPa to 1025.4 MPa, showing an increase of 12.6%. Moreover, an increase in the cooling rate has an evident promoting effect on the refinement of the precipitation phase. When the cooling rate is elevated from 50 °C/min to 250 °C/min, the average size of the γ′ phase decreases from 106 nm to 82.1 nm, and its morphology transforms from an irregular state to a spherical shape. For the microstructure of the material, such as the size of the precipitated phase and dislocation density, the maximum prediction error of the heat treatment organization performance prediction model established in this study is 2.97%. Moreover, the prediction error of the yield strength is 1.76%.

The deformation mechanism during the hot compression of PM nickel-based superalloy FGH99 and its micro-structural evolution, especially the evolution of γ’ phases, are the key factors affecting the final molding quality of aero-engine hot forged turbine disks. In this study, a new constitutive model of viscoplasticity with micro-structures as physical internal parameters were developed to simulate the hot compression behavior of FGH99 by incorporating the strengthening effect of the γ’ phase. The mechanical behavior of high-temperature (>1000 K) compressive deformation of typical superalloys under a wide strain rate (0.001~1 s⁻¹) is investigated using the Gleeble thermal-force dynamic simulation tester. The micro-structure after the hot deformation was characterized using EBSD and TEM. Work hardening as well as dynamic softening were observed in the hot compression tests. Based on the mechanical responses and micro-structural features, the model considered the coupled effects of dislocation density, DRX, and γ’ phase during hot flow. The model is programmed into a user subroutine based on the Fortran language and called in the simulation of the DEFORM-3D V6.1 software, thus realizing the multiscale predictive simulation of FGH99 alloy by combining macroscopic deformation and micro-structural evolution. The established viscoplastic constitutive model shows a peak discrepancy of 10.05% between its predicted hot flow stresses and the experimental values. For the average grain size of FGH99, predictions exhibit an error below 7.20%. These results demonstrate the high accuracy of the viscoplastic constitutive model developed in this study.