SEM/EBSD Analysis of Grain Refinement and Coarsening of Ultra-Fine-Grained Al during Simple Shear Deformation

Although severe plastic deformation causes grain refinement of polycrystalline materials, saturation of grain refinement is known to be caused by simultaneous grain coarsening. In the present study, for ultra-fine-grained (UFG) pure Al prepared by equal-channel angular pressing, we studied the grain refinement and coarsening processes during large simple-shear deformation using scanning electron microscopy/electron backscatter diffraction. The changes of the crystal orientations in the grains as a function of position were analyzed using log angles as rotation angles around reference axes. This analysis enabled the evaluation of order of magnitude of the in-plane components of geometrically necessary dislocation (GND) density tensors. Detailed changes in the crystal orientations during shear deformation were measured for identical regions in UFG Al, and the changes in the components of the GND density tensors were discussed. Our findings indicate that the grain refinement and coarsening can be explained by the appearance and disappearance of grain boundaries composed of dislocation walls, respectively.