Effect of strain rate on the microstructural evolution of hot deformed GH625 superalloy

Hot compression tests were conducted on a Gleeble-1500 simulator at a true strain of 0.7 at different temperatures and different strain rates to investigate the dynamic recrystallization behavior of GH625 superalloy. Optical microscopy (OP) and transmission electron microscopy (TEM) were employed to analyze the effect of strain rate on the microstructural evolution and nucleation mechanisms of dynamic recrystallization (DRX). The results show that the actual deformation temperature of the sample deformed at a strain rate of 10.0s^-1 is higher than the preset temperature, resulting in a deformation thermal effect. It is also found that the DRX of GH625 superalloy is controlled by both strain rate and deformation temperature. When the strain rate έ ≤ 1.0s^-1, the size and volume fraction of DRX grains decrease with increasing strain rate. The nucleation mechanism of DRX is composed of discontinuous dynamic recrystallization (DDRX) characterized by the bulging of original grain boundaries and continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation. However the size and volume fraction of DRX grains increase at a strain rate of 10.0s^-1 due to the deformation thermal effect. The nucleation mechanism of DRX for GH625 superalloy deformed at a strain rate of 10.0s^-1 is operating by DDRX with the bulging of original grain boundaries.