Effect of crystal orientation, structure and dimension on vickers microhardness anisotropy of β-, α-Si3N4, α-SiO2 and α-SiC single crystals

Variation of Vickers microhardness on planes parallel to [VMH(∥C)] and perpendicular to the C-axis [VMH(⊥C)] of hexagonal β-Si3N4, α-Si3N4, α-SiO2 (α-quartz) and α-SiC(6H) single crystals has been studied. The VMH (∥C)VMH (⊥C) ratios have been correlated with ac ratios, a and c being unit cell parameters of the single crystals. VMH(⊥C) was found to be independent of orientation of Vickers indenter on basal plane (0001) of α-SiC, while VMH(∥C) was found to vary with Vickers indenter direction on prismatic plane (10-10) of α-SiC. VMH(∥C) of β-Si3N4 single crystals was found to depend on the aspect ratio of β-Si3N4, while VMH(⊥C) was found to be independent of the dimension of basal plane. VMH(⊥C) of α-SiC single crystals was also found to be independent of the dimension of basal plane of α-SiC.