Effect of Strain Rate on Dynamic Recrystallization of a Typical γ-γ′ Nickel-Based Superalloy with Initial Bimodal Precipitation

The effect of strain rateStrain rate on microstructureMicrostructure evolution of a γ-γ′ nickel-based superalloyNickel-based superalloy during hot deformation has been examined in this study. The experiments were conducted below the γ′-phase solvus temperature, at 1050 °C with various strain ratesStrain rate ( \({10}^{-1}\) , \({10}^{-2}\) , and \({10}^{-3}\) \(\text{ s}^{-1}\) ) up to different macroscopic strain level (0.2, 0.8, and 1.3). An inverse effect of strain rateStrain rate on dynamic recrystallizationDynamic recrystallization has been observed with an increase in the recrystallized fraction as strain rateStrain rate increases, for a fixed macroscopic strain level. Scanning electron microscope and electron backscattered diffraction analysis were employed to investigate the deformed microstructuresMicrostructure in terms of γ phase evolution and γ′ precipitationΓ′ precipitation state. A constant average size value of recrystallized grainsRecrystallized grains at 1 µm is obtained for all tested conditions, suggesting that nucleationNucleation of new dynamically recrystallized grainsRecrystallized grains is favored at the expense of the growth of recrystallized grainsRecrystallized grains during hot deformation, which is inhibited. Furthermore, the complete absence of fine γ′ precipitationΓ′ precipitation within dynamically recrystallized grainsRecrystallized grains, reveals a strong interaction between the progress of recrystallizationRecrystallization front and the presence of fine γ′ precipitatesPrecipitates.