Abstract
Here, we report friction reduction observed in a ring-on-disk sliding test under hydrodynamic lubrication in distilled water with silicon-carbide (SiC) specimens with herringbone-like grooves formed by irradiation with femtosecond laser pulses, the sliding surface of which was partially treated hydrophobically with hexamethyldisilazane (HMDS) vapor, compared with the test using the hydrophilically treated specimen by exposure to UV in air. Assuming the reduction was induced by fluid slip, the slip length decreased as the normal load increased or as the sliding velocity decreased, despite no damage to the hydrophobic coating due to hydrodynamic lubrication. This dependence of slip length on the normal load suggests the existence of a low-density fluid layer on the hydrophobic sliding surface, as reported in some literature .
