Possibility of high-pressure transformation during nanoindentation of SiC

High-pressure transformation to the rocksalt structure has been proposed as a mechanism that underlies the ductile wear observed during nanomachining of SiC. However, in contrast to other brittle materials (e.g. Si), no such transformation has been directly observed either during machining or during nanoindentation of SiC. Here, we performed large-scale molecular dynamics simulations of nanoindentation with spherical indenters of various sizes and surface roughness to determine whether SiC can undergo a nanoindentation-induced transformation from the zincblende to the rocksalt structure. The calculations of possible states of stresses under the indenter have been combined with a thermodynamic analysis to estimate the effects of dislocation density, shear stresses and temperature on the phase transformation pressure in SiC. Our analysis shows that the high-pressure transformation is highly unlikely under the conditions of nanomachining. We conclude that the primary response of SiC to nanoindentation is dislocation nucleation and propagation in the low-pressure (zincblende) phase.