Energy efficiency has gained importance due to the increase in global energy demand and a decrease in fossil fuel sources over the last decade. Friction causes energy losses and decreases the energy efficiency of the mechanical system and related to friction, wear is the source of material losses at the components of the mechanical system which also determines the effective life of the system. Thus, to decrease friction losses and wear of component materials, lubricating oils blended with additives are used and surface treatments are applied to surfaces of sliding pairs. Coatings are one of the common surface treatments for tribological applications to provide lower friction coefficient and wear resistance for sliding tribo-pairs in mechanical systems. However, sliding tribo-pairs in mechanical systems can work at boundary lubricated sliding conditions, when oil film thickness decreases below 100 nm between sliding surfaces and metal to metal contacts arise with the interaction of surface asperities. In this study, AISI52100 steel surfaces were coated with bilayer Cr–N/TiB2 thin films in total thickness of 65 and 120 nm by magnetron sputtering. The CrN/TiB2 thin-films deposited under 10 and 20 sccm N2 flow whereas no N2 flow was used for a Cr/TiB2 thin film. The friction and wear behaviors of these bilayer thin-films consisting of metallic (Cr)/ceramic (TiB2) and ceramic(CrN)/ceramic(TiB2) layers were investigated via the tribometer tests under unlubricated and lubricated conditions. Bilayer thin-films were characterized by nanoindentation, microscopic and spectroscopic analysis. Results showed that N2 flow has significant effects on mechanical characteristics of bilayer coatings. Furthermore, the Cr/TiB2 thin film with a high porosity showed good tribological performance under 2 GPa contact pressure whereas the CrN/TiB2 thin film deposited at high N2 flow with high thickness and hardness showed the best tribological behavior.
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