Microstructural evolution of a Ni-Co based superalloy during hot compression at γ′ sub-/super-solvus temperatures

The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated by isothermal compression tests performed at gamma' sub-solvus (1090 degrees C) and gamma' super-solvus temperatures (1150 degrees C) with a wide strain rate range from 0.001 to 10 s(-1) under a true strain of 0.693. Electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and transmission electron microscope (TEM) techniques were used to characterize the microstructures. The results revealed that the dynamic recrystallization (DRX) volume fraction increased and stored energy of the gamma matrix grains decreased with increasing the strain rate during gamma' sub-solvus temperature deformation, while the opposite phenomena were observed during gamma' super-solvus temperature deformation. The comprehensive effect of initial grain size, primary gamma' phase, twins and adiabatic temperature rise led to these results. The primary gamma' particles undergone the deformation behavior within itself and obviously accelerated the DRX of the matrix. The microstructural evolution proved that discontinuous dynamic recrystallization (DDRX) was the dominant mechanism during the hot deformation carried out at both gamma' sub-solvus and gamma' super-solvus temperatures. Primary gamma' particles obviously accelerated the nucleation step and retarded the growth step of DDRX during gamma' sub-solvus temperature deformation. Besides, the acceleration effect of primary gamma' particles on DDRX increased with the increase of strain rate. Continuous dynamic recrystallization (CDRX) was confirmed to be an assistant mechanism during gamma' super-solvus temperature deformation and was promoted with the increase of strain rate. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The effects of strain rate on the microstructural evolution and deformation mechanism of a Ni-Co based superalloy were investigated through isothermal compression tests. It was found that the primary gamma' particles played a significant role in accelerating and retarding dynamic recrystallization (DRX), while discontinuous dynamic recrystallization (DDRX) was identified as the dominant mechanism.