Microstructure evolution and underlying mechanisms during the hot deformation of 718Plus superalloy

Abstract

718Plus superalloy was investigated to obtain a detailed and fundamental understanding of the microstructure evolution and the underlying mechanisms. Isothermal compression tests were conducted, and different strains were utilized to trace the whole deformation process at the selected deformation conditions. The results showed that no yield drop phenomenon (YDP) occurred at all deformation conditions involved in this research except a very slight one at 1020 °C with the strain rate of 0.1 s−1 The heterogeneity of initial microstructure was responsible for the absence or weakening of YDP. Deformation conditions and the Taylor factor differences between adjacent grains were found both strongly affected the distribution of dislocation density and local misorientation, as well as the formation of low angle grain boundaries (LAGBs), which finally influenced the dynamic recrystallization (DRX) behaviors and the underlying mechanisms. Moreover, discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) behaviors as well as the underlying mechanisms were discussed in detail. Subgrain rotation would also be observed during the DDRX process, which may lead to a misjudgment of CDRX if only focused on misorientation gradient. Hence, based on the morphology examination, misorientation gradient and misorientation angle evolution, progressive subgrain rotation labeled as CDRX was confirmed to be an important assistant nucleation mechanism during the deformation of the studied 718Plus superalloy at both sub-solvus and super-solvus temperatures.