Diallyl disulphide as natural organosulphur friction modifier via the in-situ tribo-chemical formation of tungsten disulphide

The present work shows a novel method for generating in-situ low friction tribofilms containing tungsten disulphide in lubricated contacts using diallyl disulphide as sulphur precursor. The approach relies on the tribo-chemical interaction between the diallyl disulphide and a surface containing embedded sub-micrometer tungsten carbide particles. The results show that upon sliding contact between diallyl disulphide and the tungsten-containing surface, the coefficient of friction drops to values below 0.05 after an induction period. The reason for the reduction in friction is due to tribo-chemical reactions that leads to the in-situ formation of a complex tribofilm that contains iron and tungsten components. X-ray photoelectron spectroscopy analyses indicate the presence of tungsten disulphide at the contact interface, thus justifying the low coefficient of friction achieved during the sliding experiments. It was proven that the low friction tribofilms can only be formed by the coexistence of tungsten and sulphur species, thus highlighting the synergy between diallyl disulphide and the tungsten-containing surface. The concept of functionalizing surfaces to react with specific additives opens up a wide range of possibilities, which allows tuning on-site surfaces to target additive interactions. (C) 2017 Elsevier B.V. All rights reserved.