Hot Deformation Characteristics of GH4975 Nickel-Based Superalloy in the Coexistence Region of γ and γ′ Phases

To provide a theoretical guidance for the hot deformation of the difficult-to-deform GH4975 superalloy, hot compression tests of homogenized GH4975 ingot were performed at the γ and γ′ coexistence temperatures of 1120–1210°C, the strain rates of 0.001–10 s⁻¹, and the strain of 0.60. Arrhenius-type constitutive equation and hot processing maps have been constructed based on the corrected flow stresses. The microstructure evolution and dynamic recrystallization (DRX) characteristics have been investigated by considering the role of the γ′ phase. The results reveal that the flow stresses continuously decrease with decreasing the strain rate and increasing the temperature, and that the hot deformation activation energy is 1376.37 kJ mol⁻¹. The optimum deformation parameters are located at the region with temperatures of 1150–1210°C and strain rates of 1–10 s⁻¹. This region takes into account the high power dissipation efficiency and high stability of processing maps, as well as low crack sensitivity and high DRX fraction of the microstructure. Moreover, the primary DRX mechanism of the alloy is discontinuous DRX (DDRX), which exists widely in various deformation conditions. Continuous DRX (CDRX) and particle-induced DRX (PIDRX) play an auxiliary role, and the effect of them weakens or even disappears with decreasing the strain rate and increasing the temperature.