Asymmetrical plastic deformation during spherical micro-indentation of magnesium.

The complex deformation of magnesium (Mg) and its alloys has been the focus of many studies in lightweight technologies. In this paper, spherical micro-indentation tests followed by post-test electron microscopy were carried out on large grain pure Mg to isolate the effects of crystal orientation on the activation of deformation along different slip or twinning systems. Both pre- and post-indentation crystal orientations were measured using electron backscatter diffraction (EBSD). The pre-indentation orientations were mapped into a crystal plasticity finite element (CPFE) model to further analyze the results. It is shown that the resulting deformation twinning and the degree of indentation-induced misorientation were strongly correlated with the crystal orientation in the region of the indentation. Depending on the crystal orientation, multiple waves of basal slip were observed to form asymmetrically around the indents. These slip bands lead to more than 12° lattice rotations that are captured by CPFE modeling. For the first time, it is shown that indentation can lead to significant out-of-plane displacement field that can induce twin nucleation at the interface of far-field (>100 μm) neighbouring grains. CPFE simulations indicate that maintaining far-field strain compatibility leads to the nucleation of twins rather than a slip transfer or slip-induced twinning mechanism. • CPFE and micro indentation are used to characterize deformation mechanisms of pure magnesium. • EBSD is used to measure orientation distribution before and after indentation within individual grains. • Asymmetric plastic deformation occurs with the formation of slip bands, twins, and misorientation fields around indents. • A new mechanism for nucleation of twins in neighbouring grains is discovered. • Numerical modeling shows this nucleation results from out-of-plane displacement, not a slip-induced twinning. [ABSTRACT FROM AUTHOR]