Potential-Controlled Boundary Lubrication Using MoS 2 Additives in Diethyl Succinate
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ORIGINAL PAPER
Potential‑Controlled Boundary Lubrication Using MoS2 Additives in Diethyl Succinate Chenxu Liu1 · Yonggang Meng1 · Yu Tian1 Received: 3 March 2020 / Accepted: 14 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The active control of friction in oil-based lubricants was realized in the present study with the use of MoS2 particle additives and the application of an electric field. By modifying the surface charging state of the MoS2 particles, the dependence of potential-controlled boundary lubrication behavior on the electrical properties of the particles was demonstrated. For a diethyl succinate lubricant containing negatively charged M oS2 particles, the coefficient of friction (COF) was reduced by 60–70% when a positive potential was applied to a lower friction pair of copper plates. After modification with poly(diallyldimethylammonium chloride), the particles were positively charged, and the COF was reduced with the application of a negative potential. The mechanisms underlying the potential control of the COF were investigated by observing the distributions of the particle additives and characterizing the tribofilms formed at different potentials. Most of the charged particles were locally concentrated near the opposite pole, and this was reversed when the electric field changed. For locally high concentrations of M oS2 particles, a M oS2/MoOx tribofilm with a thickness of 100–500 nm and a loose structure formed on the lower friction pair, which significantly decreased the shear force during the friction process. Graphical Abstract
Keywords MoS2 additive · Surface design · Potential controlled behavior · Boundary lubrication · Tribofilm Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11249-020-01313-w) contains supplementary material, which is available to authorized users. * Yonggang Meng [email protected]; [email protected] 1
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
1 Introduction Boundary lubrication exists in almost all frictional interfaces in machine elements. For reciprocating or oscillating components, such as piston ring/cylinder bore in combustion engines and hydraulic pumps, or oscillating joint bearings,
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boundary lubrication dominates near the two ends of displacement in each moving cycle due to the kinetics. Even for rotational journal and rolling element bearings that normally operate in hydrodynamic lubrication regime, they temporarily experience boundary lubrication state when machines are started up or shut down. Boundary lubrication also often appears in machine elements whenever they are overloaded, starved in lubrication or operated in severe conditions. To reduce friction and wear in the presence of boundary lubrication, various friction modifiers, antiwear additives, and extreme pressure additives have been developed and are widely used in industry. There are four commo
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