Influence of morphology and microstructure on the tribological behavior of arc deposited CrN coatings for the automotive industry

Abstract

PVD coatings are widely used in the automotive industry for tribological purposes. In heavy-duty diesel engines, piston rings represent a challenging component concerning its tribological performance. Top piston rings were designed as an additional part with a supporting role in the sealing or prevention of gas leakages from the combustion chamber. Several sudies have been published proposing metal nitride coatings for the piston ring's functional surface. CrN coatings are among those most frequently proposed, but regularly using magnetron sputtering as the predefined deposition method. In a large-scale production framework, different deposition methods with improved deposition rates must be adopted. Cathodic arc deposition is currently widely implemented in several industries, such as in the automotive one. Although this technique is consolidated in the industrial environment, the deposition process and parameters are continuously under optimization.In the present study,two different CrN coatings deposited on the piston ring's functional surface are studied. Using other deposition conditions, two distinct morphologies are achieved in the coating layer: a denser structure (CrN-A) and a columnar structure (CrN-B). Those coatings were tested using a locally developed test rig, adapted to test the piston rings under conditions close to the real engine operation. The microstructure and mechanical properties of the CrN-A and CrN-B coatings were evaluated using X-ray diffraction and micro-indentation. The surface morphology and wear mechanism were characterized using SEM and EDS techniques before and after to perform the wear and friction tests.