THE SCUFFING RESISTANCE OF THE COATED TRIBOSYSTEMS LUBRICATED WITH ECOLOGICAL OILS Remigiusz Michalczewski, Marian Szczerek, Waldemar Tuszynski, Jan Wulczynski Tribology Department Institute for Terotechnology (ITeE) Radom, Poland ABSTRACT The objective of the paper is to show that thin, hard coatings deposited on heavy-loaded machine components working in a non-conformal contact (e.g. gears) and lubricated with ecological oils, make it possible to increase the service-life of these components. The scuffing resistance was assessed by employing a high- resolution four-ball test method realized in a tester with continuously increasing load. Also another test method - FZG scuffing test - was realized using a back-to-back gear test rig. The test balls and gears were coated with thin, hard TiN and WC/C coatings deposited using arc-vacuum and reactive sputtering techniques respectively. The performed tests indicate that the presence of thin coatings on machine components gives a possibility of eliminating or reducing the content of toxic AW/EP additives in lubricating oils, as well as using ecological oils made of renewable resources, without any risk of a scuffing failure. INTRODUCTION Increasing attention to the environmental issues and more restrictive environmental regulations drive the lubricant industry to increase the ecological friendliness of its products, this means eliminating or drastically limiting the content of AW/EP additives. However, the elimination of lubricating additives from the oils implies that they may show poor performance under extreme-pressure conditions, which radically reduces the area of their application. So, the authors postulate a new concept: taking over the function of lubricating additives by thin, hard coatings deposited on sliding elements, and through this promote the application of lubricants without environmentally hazardous additives. EXPERIMENTAL Coatings with thickness about 2 μm were deposited by the PVD techniques: TiN (arc-vacuum method) and WC/C (reactive sputtering method). A four-ball tribotester working in a sliding contact (Fig. 1) was used for the basic experiments. Figure 1. Four-ball sliding tribosystem. The scuffing resistance was characterized by the so-called limiting pressure of seizure (p oz ). This measure is determined according to a test method described in detail in [1]. The higher p oz value, the better action of the tested lubricant under extreme pressure conditions. The results were verified using a back-to-back gear test rig of FZG type (Fig. 2) where the resistance to scuffing for lubricated test gears was investigated. Figure 2. Test tribosystem of the gear test rig. 1 Copyright © 2005 by ASME Proceedings of WTC2005 World Tribology Congress III September 12-16, 2005, Washington, D.C., USA WTC2005-63432