Microstructure evolution and dynamic recrystallization mechanism induced by grinding of Ni-based single crystal superalloy

Ni-based single crystal superalloy has experienced high temperature and extreme strain rate during grinding process, resulting in white layer and plastic deformation layer on the subsurface. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD) techniques were used to characterize the microstructure changes such as dislocation distribution, crystal structure and orientation information at the nanoscale of the ground subsurface. The mechanism of dynamic recrystallization and grain refinement of the single crystal superalloy were obtained. The results show that the high-density dislocation structure is easy to form in the stress concentration areas, which are the nucleation sites of dynamic recrystallization. With the accumulation of misorientation, the subgrain boundaries (SGBs) are transformed into low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs). Moreover, equiaxed nanograins are formed near the top surface due to the cooperation mechanism of dislocation movement and twins. Under the condition of high strain rate, the deformation mechanism of Ni-based single crystal superalloy is continuous dynamic recrystallization (CDRX) dominated by subgrain rotation. This work illustrated the grinding-induced microstructure evolution and mechanism of dynamic recrystallization, which provides theoretical guidance for machining of single crystal blade.