DLC (Diamond-like-carbon) is one of the candidates of coatings durable for the water lubrication. DLC-coating is known as a material for unique mechanical, chemical and electrical properties. It also has favorable properties for tribology such as low friction coefficient, high wear resistance and so on. Therefore, it is expected that DLC-coating can be used for various applications under different conditions. However, properties of DLC-coating vary widely depending on the deposition methods and deposition conditions. In addition, small particles called droplets are generated on the surface. The lubrication mechanism of DLC-coating under water lubrication has not been established sufficiently yet. Some studies have shown that a transfer layer may be responsible for the low friction and wear of DLC-coating. However, the structural composition of the transfer layer is still undefined. In this study, it was attempted to clarify the contribution of surface effect on the tribological characteristic of DLC-coating by changing the counter material under water lubrication, and by polishing the DLC-surface. It was considered that surface polishing was an effective technique for removing droplets on the surface, as well as for unifying the surface condition. In this study, polishing with diamond slurry aqueous liquid was introduced. Moreover, in order to evaluate the effect of transfer layer furthermore, different counter materials were applied for tribological tests and transfer layers on counter materials were analyzed.
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