Plastic deformation in surface indentation of magnesium oxide single crystal

In order to investigate how to achieve volume plastic flow and what kind of deformation mechanism in the Vickers indentation of a magnesium oxide single crystal, the transmission electron microscopy (TEM) images were recorded. Significant crystal plane deviation was observed in the contact area between the sample and the indenter, while there was almost no deviation in other plastic zones. It was found that the deflecting lattice interface was realized by dislocation accumulation, and incoherent in the interface is coordinated by mismatch and multi-atom layer stacking. Some narrow holes in which both ends connected to boundaries were observed, and formation of the narrow holes is due to fracture and then re-bonding under high stress. There exists an amorphous trend in the area next to the indenter, which is generated by high stress extrusion. These mechanisms together enable plastic deformation of magnesium oxide single crystals in indentation experiments.