PVD CrxN coatings for tribological application on piston rings

Besides the established PVD coatings for the wear protection of machining tools, this paper deals with coating development and model wear test results from PVD coatings on piston rings for combustion engines. Piston rings are examples for the application of thin films on commonly used mechanical components. The PVD CrxN coatings are deposited by RF magnetron sputtering and characterized by their fundamental mechanical properties like thickness, hardness, residual stress and adhesion, which are important for the tribological behaviour of the coating substrate compound. The contact mechanics of the tribological system piston-ring-cylinder are determined by high mechanical loading and changing geometry caused by the sliding kinematics. Therefore, the range of thickness is about 7 mu m. The selected rings are made of steel DIN 1.4112 (DIN X 90 Cr Mo V 18) with a bore diameter of 97.5 mm. The results of the coating substrate characterization - high hardness, moderate compressive residual stresses and sufficient adhesion on metallic substrates - provide good behaviour of coatings in this tribological application. This is confirmed by the results of the tribological test procedures which have been performed with ring-on-disc model-wear tests and a short-stroke lest rig. (C) 1997 Elsevier Science S.A.