PVD COATINGS FOR LUBRICANT-FREE TRIBOLOGICAL APPLICATIONS

This paper outlines the potential of hard coatings for ball bearings t o achieve lubricant-free employment. The examined bearing type is an a xial ball bearing (type no. 51107). This bearing combines a rolling an d a sliding movement of the balls that induces a dynamically normal an d shear stress into the coating. The rings consist of 100Cr6, a typica l bearing steel. The ball consists of Si3N4 bulk material. A special t est bench was developed to examine the coated axial ball bearings. Thi s test bench permits the investigation of very different test conditio ns by varying several parameters, such as axial force and speed of rot ation. The coatings were deposited using the magnetron sputter ion pla ting technique. At the first stage the coating material systems were d eveloped and adapted to the substrate material and its heat treatment. The optimised process was than used for coating the bearing rings. Th e reduction of the substrate temperature below its tempering temperatu re of 180 degrees C during the coating was a very important aspect. Th erefore the rings could be coated without having their hardness reduce d. After the preliminary experiments the coated rings were tested in t he test bench and compared with an uncoated bah bearing. During the te st no lubricant was used. (C) 1997 Elsevier Science S.A.