Wear resistance of PVD-coatings in roller bearings

To what extent PVD-coatings are able to take over the function of EP/AW-additives, was systematically examined on the basis of cylindrical roller thrust bearings. The bearings were tested under heavy-duty conditions in order to distinguish the efficiency of different coating-substrate-systems very fast. Out of the investigated ones, two Me-C:H-coatings showed the best performance and fulfilled the required criteria for rolling bearings in the boundary friction. Least wear took place, if only the bearing washers were coated. Material transfer from the carbonaceous coating to the steel surface developed during the test. As a consequence, a change in material combination and a smoother contact with less contact stress could be observed. The positive experiences that were made in gear wheels with microblasting could not be confirmed by the bearing tests. The performance of the coated bearings decreased. The early failure of the PVD-coatings on the microblasted surface was most likely due to the greater roughness.