DDRX and CDRX of an as-cast nickel-based superalloy during hot compression at γ′ sub-/super-solvus temperatures

Abstract

Taking the importance of γ′ phase into consideration, an as-cast nickel-based superalloy was investigated by uniaxial compression experiments performed at sub-solvus and super-solvus temperatures. Several different strains were utilized to trace the processes of deformation and microstructural evolution. Electron backscatter diffraction was employed to characterize the microstructures. The results reveal that the volume fraction of DRX grains increased with strain at both sub-solvus and super-solvus temperatures, and also the fraction of high angle grain boundaries. Meanwhile, both the correlated and uncorrelated misorientations gradually approached the random distribution curves during continuous strains. Specially, the fast migration of grain boundaries caused by the unpinning from γ′ particles promoted twin nucleation and generated a number of twins at sub-solvus temperatures. Sub-solvus deformations were found to be more efficient to weaken the initial textures of as-cast superalloys. Finally, it was confirmed that discontinuous dynamic recrystallization (DDRX) dominated the DRX process during the hot deformation carried out at both sub-solvus and super-solvus temperatures. Continuous dynamic recrystallization (CDRX) was the second mechanism, and played a very important role during plastic deformation at sub-solvus temperatures, which is different from the DRX mechanisms reported in the fine-grain structures of wrought billets. The findings improve the understanding of DDRX and CDRX, which does benefit to the accurate control of microstructures of nickel-based superalloys, and also tailoring the properties of final components used in aero-engine.