Direct simulation of Monte Carlo analysis of nano-floating effect on diamond-coated surface

Abstract It is well known that the diamond-coated sliding surface has good quality with respect to sliding movement. We have ensured that the partly polished diamond-coated sliding surface shows much lower coefficients of the kinetic friction than the teflon-coated sliding surface in our experiments. Also, we confirmed that the gas-layer lubrication effect appears due to the gas in the concavo–convex sliding surface when its relative counter speed reaches in the order of 1 m/s. Then, in this study, the numerical investigation was performed to simulate the gas-layer lubrication effect on the sliding surface. The microscopic flow conducted in this study has very small length scale which is in the order of the mean-free path of the air at the atmosphere pressure. Consequently, the Navier–Stokes equations are not applicable to analyze the present microscopic flow because the continuum flow is assumed. In addition, we observed many unpolished concave parts on the diamond-coated surface after polishing, and the vertical flow will appear induced by such complicated geometric boundary. For this reason, any analytical method that assumes quasi-parallel flow cannot be applied to the present flow problem. Herein, we used direct simulation of Monte Carlo (DSMC) method to handle the nano/micro flow, which cannot be assumed to be continuum. We clarified the feature of gas-layer lubrication on the sliding surface, which would be dominated by the surface roughness, the relative counter speed of surfaces, and the surface roughness including its surface geometry in the nano/micro scales.