Evolution of hot processing map and microstructure of as-forged nickel-based superalloy during hot deformation

Abstract

Nickel-based superalloy has excellent mechanical properties at high temperature. However, the high deformation resistance, narrow deformation temperature range and complex microstructure evolution of the alloy bring great challenge to the plastic deformation of the alloy. The microstructure evolution and hot deformation behavior of as-forged nickel-based superalloy were examined through thermal compression tests at 950–1150 °C and strain rates of 0.001–10 s−1 with true strain of 1.0. The stress-strain curve exhibited a yield stage under small strain, and it comprised dynamic recovery (DRV) and dynamic recrystallization (DRX) two types. Strain rate sensitivity (m) and power dissipation efficiency (η) were calculated, and hot processing map was generated in accordance with the Murty criterion, and the rate of strain and the temperature of deformation were obtained as 1100–1150 °C and 0.02–0.4 s−1, separately, based on the optimal hot processing parameters. The instability zone was primarily in the zone of high strain rates. As the temperature of deformation was risen or the rate of strain was decreased, the DRX grain size was increased, as indicated by the microstructure results. The main deformation mechanism varied from DRX to DRV, and, then to the shear band (SB), deformation band (DB), and flow localization (FL) as η was decreased. Moreover, continuous dynamic recrystallization (CDRX) at subgrains rotation and discontinuous dynamic recrystallization (DDRX) at grain boundaries were identified during thermal deformation.