Brittle-ductile transition during diamond turning of single crystal silicon carbide

In this experimental study, diamond turning of single crystal 6K-Sic was performed at a cutting speed of I mis on an ultra-precision diamond turning machine (Moore Nanotech 350 UPL) to elucidate the microscopic origin of ductile-regime machining. Distilled water (pH value 7) was used as a preferred coolant during the course of machining in order to improve the tribological performance. A high magnification scanning electron microscope (SEM FIB- FF1 Quanta 3D FEG) was used to examine the cutting tool before and after the machining. A surface finish of Ra=9.2 nm, better than any previously reported value on Sic was obtained. Also, tremendously high cutting resistance was offered by Sic resulting in the observation of significant wear marks on the cutting tool just after 11cm of cutting length. It was found out through a DXR Raman microscope that similar to other classical brittle materials (silicon, germanium, etc.) an occurrence of brittle-ductile transition is responsible for the ductile-regime machining of 6K-Sic. It has also been demonstrated that the structural phase transformations associated with the diamond turning of brittle materials which are normally considered as a prerequisite to ductile- regime machining, may not be observed during ductile-regime machining of polycrystalline materials.