Nanoindentation induced deformation anisotropy in β-Si3N4 ceramic crystals

The influence of crystal orientation on nanohardness and indentation modulus of grains in polycrystalline β-Si3N4 was studied under nanoindentation at room temperature. The orientation of the individual grains was determined by electron backscatter diffraction (EBSD) prior to the indentation. Significant elastic and plastic deformation anisotropy was revealed. The elastic modulus exhibited a decrease for grains oriented from the basal towards the prismatic facets while the nanohardness values showed reversed tendency. The orientation dependence of indentation modulus was predicted by the Vlassak-Nix model and finite element model (FEM) calculations based on the elastic constants of β-Si3N4 single crystal and compared to the experimental results. A theoretical model was proposed to describe the nanohardness anisotropy on the basis of the possible slip systems of β-Si3N4. The calculations for elastic and plastic anisotropy are in good agreement with the experimental results.