The evolution of microstructure and texture induced by grinding and subsequent thermal exposure of single crystal alloy

The dynamic recrystallization (DRX) behavior during grinding and static recrystallization (SRX) behavior during thermal exposure of Ni-based single crystal alloy were compared in this work. The microstructure changes after DRX and SRX were characterized by field emission scanning electron microscopy (FE-SEM) and scanning transmission electron microscopy (STEM). The grain orientation and dislocation density distribution were analyzed by transmission Kikuchi diffraction (TKD) and electron backscatter diffraction (EBSD). The results show that SRX is affected by DRX process on the ground subsurface of single crystal alloy. The nucleation sites of SRX at high temperature are derived from significant number of high-density dislocation structures generated by DRX that induced by grinding process. Compared with the equiaxed nanograins produced by DRX, micron-scale cellular and equiaxed grains are formed on the surface, and dislocation density decreases sharply after SRX. The original cube texture of single crystal superalloy changes into shear texture due to plastic deformation during grinding, and then into strong recrystallization texture at high temperature. The microstructure changes under deformation and high temperature directly affect the final properties of single crystal blades. It is of great practical significance to understand the microstructure evolution and grain orientation changes during DRX and SRX processes, so as to reveal the mechanism of single crystal transforming into polycrystal from machining process to service stage of single crystal blades.