Investigation of pure sliding and sliding/rolling contacts in a DLC/Cast iron system when lubricated in oils containing MoDTC-Type friction modifier. (June 2018)

• Record Type: Journal Article
• Authors: Al-Jeboori, Yasir; Kosarieh, Shahriar; Morina, Ardian; Neville, Anne
• Is Part Of: Tribology international. Volume 122(2018)
• Page Start: 23
• Page End: 37
• Publication Date: 2018-06
• Subjects: Sliding/rolling -- Pure sliding -- DLC/Cast iron -- MoDTC; Tribology -- Periodicals; 621.89
• DOI: 10.1016/j.triboint.2018.02.015
• Languages: English
• ISSNs: 0301-679X

Abstract

Abstract: Diamond-like carbon (DLC)/cast iron (CI) systems have been widely investigated due to their important application in engine components such as cylinders, pistons and more specifically for the cam/follower interface. The pure sliding contact of the DLC/CI system has traditionally been the focus of research; consequently less is understood about sliding/rolling contact systems. In addition, the tribological and tribochemical characteristics of the Molybdenum Dialkyl Dithiocarbamate (MoDTC) as a lubricant additive in such sliding/rolling contacts are not fully understood. In this study, a Mini Traction Machine (MTM) was used to run the experiments using alloy steel balls coated with 15 atomic percent (at. %) hydrogenated DLC (a-C: 15H) rubbing against uncoated cast iron discs. Results showed that the sliding/rolling ratio affects friction, wear and tribochemistry in CI/DLC systems; pure sliding enhances MoDTC activation. MoDTC decomposes to form MoS2, FeMoO4 and not MoO3 . In addition, it was observed that MoS2 /FeMoO4 ratio depends on test conditions and affects to the friction performance. Highlights: An approach to study and compare the tribological behaviour of two types of the DLC/cast iron contacts (pure sliding contact + sliding/rolling contact) under mixed-boundary lubrication regimes. In both contacts, the variation of tribofilm compositions when lubricated in a fully formulated oil / base oil containing MoDTC was investigated. The sliding/rolling ratio affects friction, wear and tribochemistry in CI/DLC systems; pure sliding enhances MoDTC activation. The main MoDTC decomposition products are MoS2 and FeMoO4, but not MoO3.