Behaviors of carbon atoms induced by friction in mechanical polishing of diamond

Abstract

Molecular dynamics simulation is employed to represent the mechanical polishing of diamond crystal, in which two diamond substrates with free surface of {100} and {110} faces are established. Firstly, the polishing direction related to variations of friction force on the both substrates are analyzed, and the non-diamond carbon atoms produced due to the phase transformation, mainly sp2 and amorphous sp3 hybridizations, in the surface layer are further extracted. Then, the distribution planes of ordered sp2 hybridizations are fitted, on which the length and angles of C–C bonds are also calculated. Finally, dependence of the length of dislocation lines and the distribution area of localized von Mises shear strain in the polishing direction are discussed. The results suggest that friction force decreases gradually when the polishing direction transiting from the ‘soft’ direction to the ‘hard’ direction, and the same variation tendency is also observed on the phase transformation, length of dislocation lines as well as distribution area of localized shear strain. More interestingly, the appearance of ordered sp2 structures, which can be considered as graphitization of diamond, has an obvious directionality. It always generates on the {100} crystal planes, regardless of polishing on the {100} and {110} faces.