Tribological behavior of thick DLC coatings under lubricated conditions

The experiments showed that under same tribological parameters all lubricated DLC coatings on polished samples suffered under strong fatigue wear on the surface. By using thick coatings, it could be realised that this is not caused by an adhesion problem, because the resulting defects do not reach the steel interface. Fatigue wear was found for lubrication with oil as well as for lubrication with water. In contrast DLC coated rough surfaces showed no fatigue wear, also under lubricated condition. By using rough DLC coatings the wear of the counterpart is obviously remarkable increased. If the tribological experiments were done under excessive use of oil (not on a thin oil film), no fatigue wear on the surface could be found as well. On smooth surfaces the adhesion forces caused by the thin oil or water film seem to be responsible for the observed fatigue wear defects. It is also shown that with a special topography of the DLC coating fatigue wear under slightly lubricated condition can be eliminated and simultaneously the wear of the counterpart can be kept very low.