Characteristic and mechanism of dynamic recrystallization in a newly developed Fe-Cr-Ni-Al-Nb superalloy during hot deformation

Highlights: • The Avrami kinetics model of the Fe-Cr-Ni-Al-Nb superalloy was constructed, which revealed the three stages of DRX, including nucleation, grain growth and grain contact. • Twin boundaries were found in the DRX grains under the strain of 0.3, which would consume the stored energy, thus inhibiting the growth of grains. • The generation of ∑3 derived from "growth accents" during hot deformation. • The twins found near the original grain boundaries could promote the bulging behavior and accelerate the separation of the bulged sites from the matrix, which was beneficial for DRX. • Three different DRX mechanisms were identified. DDRX was found the dominant nucleation mechanism, while CDRX and TDRX were evidenced as the auxiliary mechanism. -- Abstract: Thermal-mechanical experiments of a newly developed Fe-Cr-Ni-Al-Nb superalloy were conducted on a Gleeble simulator under the temperature of 900–1100 ℃ and the strain rate of 0.01–5 s⁻¹. The microstructure evolution and the nucleation mechanisms of dynamic recrystallization (DRX) were characterized by electron backscattering diffraction (EBSD) technique, and the results showed that relatively higher temperature, lower strain rate and larger true strain were favorable for DRX. When the superalloy was deformed under 1050 ℃− 0.1 s⁻¹, nearly complete DRX occurred with the power dissipation efficiency of 0.34. Moreover, the Avrami dynamic model of the investigated superalloy was constructed, which suggested that there were three stages during DRX, including nucleation, grain growth and grain contact. Furthermore, three different DRX mechanisms during hot deformation were identified. The bulge and nucleation characteristics of original grain boundaries occurred within all experimental parameters, confirmed that discontinuous dynamic recrystallization (DDRX) was the main DRX mechanism. Besides, the presence of a small amount of medium angle grain boundaries affirmed that subgrains continuously rotated and absorbed dislocations during deformation, meaning that the continuous dynamic recrystallization (CDRX) was an auxiliary nucleation mechanism. Moreover, annealing twins, appeared in the matrix, provided additional nucleation sites for DDRX and CDRX, encouraging the twinning dynamic recrystallization (TDRX), which effectively promoted the progress of DRX.