The contribution of γ' phase transition induced (PI-CDRX) - CDRX-DDRX alternating cycling behavior to the hot formability of GH4079 alloy

Abstract

The hot deformation behavior of nickel-based superalloys at different temperatures (1025–1150 °C) and different strain rates (0.001–1 s⁻¹) was studied by isothermal hot compression experiments using a Gleeble-3800 thermal simulator. According to the obtained stress-strain curve, the Arrhenius constitutive model based on the phase transition temperature segmentation was established. The correlation coefficient and the average absolute error were 0.992 and 0.978, respectively. Based on the thermal processing theory, the thermal processing maps based on Prassad, Gegel, Murty and Malas instability criteria were constructed and the rheological instability conditions of materials were predicted. The microstructure nucleation mechanism of DRX was studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that due to the strong pinning effect of γ' phase on grain boundaries and the interaction between γ' phase and dislocations, the hot deformation behavior of the material at the phase transition temperature (1067 °C) is significantly different. The PI-CDRX (γ' phase-induced continuous dynamic recrystallization) and CDRX (continuous dynamic recrystallization) mechanisms dominate below the phase transition temperature. The DRX mechanism above the transformation temperature is mainly DDRX (discontinuous dynamic recrystallization), and the degree of DRX gradually increases with the increase of the deformation temperature. In addition, the ∑3 twin boundaries contribute to the nucleation of DRX grains.