Forming limit curves (FLC) at high temperatures under plane-stress states are beneficial for guiding the process parameter design of hot forming superalloy sheets. Constrained by the high deformation temperatures, the establishment of FLCs of superalloy sheets at high temperatures is extremely difficult. This paper conducts an experimental and modelling research to establish the physical-based model with the accurate prediction of hot flow behavior as well as micro grain sizes, using which, the forming limit curves can be predicted. First, the uniaxial tensile tests under different temperatures and strain rates and electron backscattered scattering detection (EBSD) observations of typical conditions were conducted to obtain the hot flow behavior and grain evolution. Second, the dome test at room temperature was performed, and the corresponding simulation was further carried out to obtain the forming limit at room temperature under plane-stress states. Using the above results, a plane-stress constitutive model for GH3128 superalloy was established enabling plane-stress test results under typical hot conditions to be accurately predicted. The prediction accuracies of hot uniaxial and biaxial stretching results are 94.2% and 95.4%, respectively.

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.