Characteristics of friction surfaces with DLC films in low and high humidity air

Diamond-like carbon (DLC) films were deposited on Si wafers using a plasma CVD apparatus with two different types of precursors. A friction and wear test was conducted under dry and wet air conditions. In wet air, friction was higher and the wear rate was smaller than that experienced in dry air. The rupture load of DLC films, were a normal load was increased stepwise, was larger with wet air than dry air. Many folds, perpendicular to the sliding direction, were seen on the friction surfaces under wet air conditions, although the friction surfaces in dry air seemed very smooth. There were no pits on the friction surface in wet air, although some pits existed on surfaces exposed to dry air. Even with the endurance test, there were no pits and clacks on the friction surface in wet air, in contrast to the friction surface in dry air. Many of the wear fragments obtained in wet air had a flattened-shape, while many granular wear fragments were scattered on the friction surface in dry air. These observations suggest that the friction surface obtained under wet air conditions has the property that can deform plastically. This property translates to a smaller wear and a greater film toughness.