The mechanism of ductile deformation in ductile regime machining of 6H SiC

Silicon Carbide (SiC) is a material with excellent mechanical and electrical properties. Much attention has been paid to the ductile regime machining of SiC in recent years, but there is still controversy regarding the mechanism of its ductile response in ultraprecision machining. While some researchers proposed the high pressure phase transformation (HPPT) theory from experimental studies on 6H SiC, later molecular dynamics (MD) studies disapproving the HPPT theory adopted 3C SiC as the workpiece. This study conducts MD simulations to investigate the atomicscale details of ductile deformation in the machining of 6H SiC for the first time, using an interaction potential that can reproduce the HPPT of SiC. The HPPT in the machining of 6H SiC are visualized for the first time by MD simulations, although the quantity of HPPT is very small. The dislocation structures in the machining of 6H SiC are also visualized by MD for the first time. Frank partial dislocations and basal plane edge dislocations are identified to be primarily responsible for the ductile deformation. Taper cutting experiment on a single crystal 6H SiC wafer produces a ductile-cut surface, and micro Raman spectroscopy on the machined surface finds no peaks for amorphous SiC, which agrees with the MD result that the quantity of HPPT is very small. These results indicate that the origin of ductile response for 6H SiC is a combination of HPPT and dislocation activities, while dislocation plasticity plays a major role. (C) 2014 Elsevier B.V. All rights reserved.