Formation of interfacial molybdenum carbide for DLC lubricated by MoDTC: Origin of wear mechanism

• Published in: Wear Vol. 370-371; pp. 17 - 28
• Main Authors: De Feo, M., De Barros Bouchet, M.I., Minfray, C., Esnouf, C., Le Mogne, Th, Meunier, F., Yang, L., Thiebaut, B., Pavan, S., Martin, J.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-01-2017; Elsevier Science Ltd; Elsevier
• Subjects: Additives; Boundary lubrication; Chemical composition; Chemical elements; DLC coatings; Energy dispersive X ray spectroscopy; Energy transmission; Engineering Sciences; Lubrication; Materials; MoDTC friction modifier additive; Molybdenum; Molybdenum carbide; Molybdenum dithiocarbamate; Organic chemistry; Protective coatings; Transmission electron microscopy; Tribology; Wear mechanism; Wear mechanisms; Wear rate; Wear resistance; X ray photoelectron spectroscopy; X ray spectra; MoDTC friction modifier additive; DLC coatings; Wear mechanism; Additives; Energy dispersive spectroscopy; Friction modifier additives; X ray spectroscopy; Amorphous silicon; Wear mechanisms; Coatings; Tribological experiments; Carbon; Boundary lubrication conditions; Friction and wear performance; Transmission electron microscopy; Molybdenum dithio carbamates; Friction; Wear of materials; X ray photoelectron spectroscopy; High resolution transmission electron microscopy; Lubrication; Carbides; Tribology; Energy dispersive X ray spectroscopy
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2016.10.002

A large amount of research has been devoted to the effect of molybdenum dithiocarbamate (MoDTC) additives on the lubricating performances of carbon-based coatings, showing that a high wear rate is produced when the MoDTC is blended with the base oil. However, the mechanisms leading to the coating removal are not fully understood yet.
In this work, the friction and wear performances of an amorphous hydrogenated DLC coating doped with silicon and oxygen have been analysed when lubricated by MoDTC-containing oils. Tribological experiments have been conducted with DLC/steel and DLC/DLC contacts under boundary lubrication conditions using a ball-on-flat tribometer. To understand the wear mechanism, the chemical composition of the tribofilm formed on the steel ball counterpart was investigated by X-ray Photoelectron Spectroscopy (XPS). Transmission Electron Microscopy (TEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDX). A new DLC wear model has been proposed and validated.
•MoC species are formed on steel ball in a steel/DLC contacts lubricated with MoDTC.•The presence of MoC is related to high wear of the DLC.•The wear mechanism is mainly due to chemical reaction between C (DLC) and Mo(MoDTC).