Diamond-coating is promising for sliding surface because it produces very low friction. Nakamori et al. found experimentally that the friction between a partly polished diamond-coated surface and a metal surface was drastically reduced to zero as relative speed was increased. In their experiment, sliding became noiseless. This indicates that the substrate with diamond coating takes off the counter surface and the sliding mechanism is gas film lubrication. In the present work, we investigate the floating mechanism and the effect of micro gas flow on friction properties by performing numerical simulations. Since the surface roughness of the partly polished diamond-coated substrates is from 0.28 gm to 0.57 gm, Knudsen number Kn is larger than 0.1. Therefore, a flow between two sliding surfaces cannot be treated as a continuum. To simulate this flow, we use the direct simulation Monte Carlo (DSMC) method.
