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

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

A Semi-deterministic Wear Model Considering the Effect of Zinc Dialkyl Dithiophosphate Tribofilm

Tribochemistry plays a very important role in the behaviour of systems in tribologically loaded contacts under boundary lubrication conditions. Previous works have mainly reported contact mechanics simulations for capturing the boundary lubrication regime, but the real mechanism in which tribofilms reduce wear is still unclear. In this paper, the wear prediction capabilities of a recently published mechanochemical simulation approach (Ghanbarzadeh et al. in Tribol Int, 2014) are tested. The wear model, which involves a time- and spatially dependent coefficient of wear, was tested for two additive concentrations and three temperatures at different times, and the predictions are validated against experimental results. The experiments were conducted using a mini-traction machine in a sliding/rolling condition, and the spacer layer interferometry method was used to measure the tribofilm thickness. Wear measurements have been taken using a white-light interferometry. Good agreement is seen between simulation and experiment in terms of tribofilm thickness and wear depth predictions

The Future of Boundary Lubrication by Carbon Coatings and Environmentally Friendly Additives

5th China International Symposium on Tribology/1st International Tribology Symposium of IFToMM, Beijing, PEOPLES R CHINA, SEP 24-27, 2008International audienceThis paper presents a tribological system that produces superlubricity under boundary lubrication conditions with extremely little wear. This system is a thin coating of Diamond-Like-Carbon in a DEC friction pair lubricated with OH-containing additives. The DLC material is hydrogen-free tetrahedrally amorphous DLC (denoted as ta-C). To identify the mechanism of friction vanishing we performed ToF-SIMS experiments on the wear scars obtained with deuterated glycerol and C-13 glycerol. The structural modifications of the ta-C coating that have been induced by the pressure and shear during the friction were also studied

MoDTC lubrication of DLC-involving contacts. Impact of MoDTC degradation

Recently Diamond-Like Carbon (DLC) coatings have attracted considerable attention due to their low friction, high hardness, good wear and corrosion resistance, and high thermal and chemical stability. Although considerable research has been conducted on the effect of molybdenum-based additives, e.g., molybdenum dithiocarbamate (MoDTC), on the boundary lubrication of DLC coatings, the wear mechanisms leading to the coating removal are not fully understood to date. Moreover, the impact of the degradation of the MoDTC-containing base oil on the tribological properties of DLC coatings has not been investigated. This study could help to elucidate the mechanisms by which the coating is worn out in presence of MoDTC-containing base oil. In this work, the friction and wear performances of DLC coatings with different hydrogen contents and doping elements have been investigated in the presence of MoDTC-containing base oil. To enable the correlation between these changes and the modification of the contact surface chemistry, tribofilms generated during friction were investigated by SEM combined with Energy Dispersive X-ray Spectrometry (EDX) and X-ray Photoelectron Spectroscopy (XPS). A new mechanism explaining the severe wear experienced by DLC coatings when lubricated with a MoDTC-containing base oil is proposed