Metal to metal contact under contact pressures results in adhesion of two surfaces that reveal adhesion wear and plastic deformation on the surfaces. Following this, abrasive wear mechanism can be caused by separated particles from the surfaces. The adhesion, depending on the surface free energy of the sliding pairs, generates higher energy losses with friction force. This energy loss and wear can be reduced by coatings that relatively decrease the surface free energy and adhesion. In this study, magnetron sputtered bilayer Cr–N/TiB2 heterostructured thin-film coatings were investigated by tribological tests, microscopic and spectroscopic analysis to evaluate their friction and anti-wear behaviors under unlubricated and boundary lubricated conditions. Especially, these heterostructured thin-film coatings were investigated to act as an alternative coating for cam tappets of internal combustion engines (ICEs) that are sliding against cam noses. This tribological system is the one main source of friction losses and runs mostly under boundary lubricating condition which leads to wear of cam tappets. According to the literature survey, TiB2 hard coatings were deposited as composite coatings on various tool steel surfaces, such as TiN–TiB2, Ti–TiB2, and TiC–TiB2 by physical vapor deposition and their tribological behaviors were investigated by tribometer tests under unlubricated conditions. Furthermore, Ti/TiB2/MoS2 graded composite coatings were deposited on Cu substrates by pulsed- DC magnetron sputtering and investigated to be an alternative coating for machining applications. On the other hand, thermal and atmospheric plasma spray coating methods have been used to develop multilayer wear and oxidation-resistant composite coatings such as NiAl–TiB2, TiC–TiB2 for structural materials and tool steels in recent studies. However, there has been no study focusing on wear and friction behavior of composite TiB2 coatings at lubricated conditions to be an alternative coating for ICEs cam tappets. Moreover, investigation of the lubricating oil and TiB2 composite coating interaction topic has been very scant in the literature. Therefore, this paper presents a novel study, which focuses on the tribological behavior of magnetron sputtered bilayer metallic (Cr)/ceramic (TiB2) and ceramic samples by magnetron-sputtering and their morphological, chemical and mechanical properties were characterized by macroscopic and spectroscopic analyses. Bilayer thin-film coated samples were tested by a tribometer to explore wear and friction characteristics of the coatings not only at unlubricated conditions but also under various loads such as 10, 25, 50 N at lubricated conditions.
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