Post-dynamic recrystallization behavior of a powder metallurgy Ni-Co-Cr based superalloy under different deformation conditions

The post-dynamic recrystallization (PDRX) behavior of a powder metallurgy (PM) Ni-Co-Cr based superalloy was researched by thermal compression tests at the temperature range of 1020–1080 °C within the strain rates of 0.01–1 s⁻¹, followed by heat preservation for 0–45 s after deformed to 10%−50%. Electron backscatter diffraction (EBSD) and Transmission Electron Microscope (TEM) techniques were employed to investigate the effect of the deformation conditions on PDRX behavior. The results show that the deformation conditions (strain rate, temperature, degree of deformation and holding time) have great impact on the PDRX kinetics. Increasing deformation temperature, strain or holding time can result in the effective release of residual deformation stored energy, promoting the PDRX course. The irregular energy storage release of the superalloy deformed at different strain rates is mainly concerned with the various microstructure evolution during heat preservation. The evolution of twin boundary (Σ3) during PDRX exhibits the similar regularity with that of recrystallization fraction. The formation of Σ3 boundary induces the recrystallized nucleation, leading to further release of deformation storage energy. Meta-dynamic recrystallization (MDRX) and static recrystallization (SRX) are the dominant mechanisms of PDRX, and the nucleation induced by undissolved γ′ precipitates or assisted by twins also play certain roles in microstructure evolution during heat preservation of the deformed superalloy.