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A number of wear resistant coatings has been developed using physical vapor deposition(PVD) process. However this coating process has not yet been widely used in the automotive industry. The purpose of this work was to evaluate thin PVD coatings such as diamond like carbon doped with tungsten (W-DLC), molybdenum-disulfide doped with aluminum (MoS2-Al), and chrome nitride (CrN). Some of these coatings were previously found to have low friction, high wear resistance, or both when tested in unlubricated conditions. In the present work, the experiments were conducted using a Cameron-Plint apparatus in lubricated conditions. The ring counterfaces used were Cr-plated and gas-nitrided compression rings. Our data also indicated that some PVD coatings with thicknesses in the same order of magnitude as the surface roughness of the liners did show some improvement in liner wear resistance. The suitability of thin coatings for liner applications needs additional study.

Ring/liner wear is a major factor in determining effective engine life. One of the primary goals of engine manufactures is to design engines for increased durability. In order to preserve knowledge that was gained over the years with current liner materials and to meet target costs, methods of improving the wear resistance of the liner material without changing the substrate from gray cast iron are attractive. In addition, stringent emission requirements pose a larger challenge to the materials community. For example, cooled exhaust gas recirculation (EGR) is one option to meet US EPA NOx emissions for the year 2002. With the application of cooled EGR technology, the present durability of current ring/liner materials may be reduced. Three methods to improve the wear resistance of gray cast iron liners are 1) adding special alloying elements 2) using surface treatment techniques such as induction hardening, gas nitriding, etc. 3) applying surface coatings.