Orientation dependence of intracrystalline and grain boundary deformation behavior in Mg-2Y using nanoindentation and CPFEM

The inherent hexagonal close-packed (HCP) structure of magnesium (Mg) alloys leads to anisotropy in their deformation mechanism. In this study, the deformation behavior of Mg-2Y alloys with varying grain orientations was investigated by using nanoindentation experiments coupled with Electron Back Scatter Diffraction (EBSD) and Crystal Plasticity Finite Element Method (CPFEM) techniques. It has been found that "Hard grains" demonstrate significantly higher hardness and elastic modulus compared to "Soft grains". This distinction is primarily attributed to the varying Schmid factors of the slip systems corresponding to different grain orientations, resulting in the anisotropy of deformation mechanism. The dominant deformation mechanism for "Hard grains" is basal slip, while prismatic and pyramidal slip dominate for "Soft grains". The activation of the corresponding slip system was confirmed by the in-grain misorientation axes (IGMA) distribution, indentation surface morphology, slip trace analysis, and CPFEM simulations. Additionally, fixed-target grain boundary indentation experiments and geometrical compatibility calculations were employed to determine that the effect of grain boundaries on plastic deformation mechanism is primarily dependent on the neighboring grains misorientation angle. The mechanism of competitive and coordinated behaviors between deformation mechanisms was also revealed.