High temperature deformation and recrystallization behavior of magnesium bicrystals with 90° <■> and 90° <■> tilt grain boundaries

The deformation mechanisms and dynamic recrystallization(DRX) behavior of specifically grown bicrystals with a symmetric 90° <■> and 90° <■> tilt grain boundary, respectively, were investigated under deformation in plane strain compression at 200 ℃ and 400 ℃. The microstructures were analyzed by panoramic optical microscopy and large-area electron backscatter diffraction(EBSD)orientation mapping. The analysis employed a meticulous approach utilizing hundreds of individual, small EBSD maps with a small step size that were stitched together to provide comprehensive access to orientation and misorientation data on a macroscopic scale. Basal slip primarily governed the early stages of deformation at the two temperatures, and the resulting shear induced lattice rotation around the transverse direction(TD) of the sample. The existence of the grain boundary gave rise to dislocation pile-up in its vicinity, leading to much larger TD-lattice rotations within the boundary region compared to the bulk. With increasing temperature, the deformation was generally more uniform towards the bulk due to enhanced dislocation mobility and more uniform stress distribution. Dynamic recrystallization at 200 ℃ was initiated in {■}-compression twins at strains of 40% and higher. At 400 ℃, DRX consumed the entire grain boundary region and gradually replaced the deformed microstructure with progressing deformation. The recrystallized grains displayed characteristic orientations,such that their c-axes were perpendicular to the TD and additionally scattered between 0° and 60° from the loading axis. These recrystallized grains displayed mutual rotations of up to 30° around the c-axes of the initial grains, forming a discernible basal fiber texture component,prominently visible in the {■} pole figure. It is noteworthy that the deformation and DRX behaviors of the two analyzed bicrystals exhibited marginal variations in response to strain and deformation temperature.