PVD coatings for lubricant-free tribological applications

Abstract This paper outlines the potential of hard coatings for ball bearings to achieve lubricant-free employment. The examined bearing type is an axial ball bearing (type no. 51107). This bearing combines a rolling and a sliding movement of the balls that induces a dynamically normal and shear stress into the coating. The rings consist of 100Cr6, a typical bearing steel. The ball consists of Si 3 N 4 bulk material. A special test bench was developed to examine the coated axial ball bearings. This test bench permits the investigation of very different test conditions by varying several parameters, such as axial force and speed of rotation. The coatings were deposited using the magnetron sputter ion plating technique. At the first stage the coating material systems were developed and adapted to the substrate material and its heat treatment. The optimised process was than used for coating the bearing rings. The reduction of the substrate temperature below its tempering temperature of 180 °C during the coating was a very important aspect. Therefore the rings could be coated without having their hardness reduced. After the preliminary experiments the coated rings were tested in the test bench and compared with an uncoated ball bearing. During the test no lubricant was used.