On the phase transformation of single-crystal 4H-SiC during nanoindentation

Microstructural changes of single-crystal 4H silicon carbide (SiC) induced by nanoindentation under various conditions were investigated. It was found that nanoindentation at different crystal orientations induced different Raman spectroscopic characteristics. Cross-sectional observation by transmission electron microscopy indicated that a very deep subsurface damage region was formed where dislocations occurring along the basal planes, crystal grains rotation and micro-cracks were observed. The microstructures of the damage regions were strongly affected by the nanoindentation conditions. Coupled analysis of lattice fringes and Raman spectra indicated that a phase transformation from 4H-SiC to 3C-SiC occurred during nanoindentation, which has never been reported before. Furthermore, the 4H to 3C phase transformation strongly depended on the indenter orientation with respect to the SiC crystal. These findings are meaningful for low-damage precision machining of SiC substrates.