Frictional properties of MoS<sub>2</sub> on a multi-level rough wall under starved lubrication

Yi, Changli; Hu, Chengzhi; Shi, Lin; Bai, Ming; Li, Yubai; Tang, Dawei

doi:10.1039/d3cp01288c

Cited by 5 publications

(2 citation statements)

References 37 publications

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“…This approach is shown in Fig. 12 c) and has been used at times in the literature for studying different types of lubricants [114,129,405,421,430]. This comes with the drawback that a single event process is studied, which brings difficulties for the sampling of statistically meaningful observables.…”

Section: Computational Tribology On the Atomistic Levelmentioning

confidence: 99%

Influence of Lubrication on Tribological Nanoscopic Contact Processes

Stephan

2024

Preprint

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Lubricated tribological contact processes are important in both nature and in many technical applications. Fluid lubricants play an important role in contact processes, e.g. they reduce friction and cool the contact zone. The fundamentals of lubricated contact processes on the atomistic scale are, however, today not fully understood. A lubricated contact process is defined here as a process, where two solid bodies that are in close proximity and eventually in parts in direct contact, carry out a relative motion, whereat the remaining volume is submersed by a fluid lubricant. Such lubricated contact processes are difficult to examine experimentally. Atomistic simulations are an attractive alternative for investigating the fundamentals of such processes. In this work, molecular dynamics simulations were used for studying different elementary processes of lubricated tribological contacts. A simplified, yet realistic simulation setup was developed in this work for that purpose using classical force fields. In particular, the two solid bodies were fully submersed in the fluid lubricant such that the squeeze-out was realistically modeled. The velocity of the relative motion of the two solid bodies was imposed as a boundary condition. Two types of cases were considered in this work: i) a model system based on synthetic model substances, which enables a direct, but generic, investigation of molecular interaction features on the contact process; and ii) real substance systems, where the force fields describe specific real substances. Using the model system i), also the reproducibility of the findings obtained from the computer experiments was critically assessed. In most cases, also the dry reference case was studied. Both mechanical and thermodynamic properties were studied – focusing on the influence of lubrication. The following properties were studied: The contact forces, the coefficient of friction, the dislocation behavior in the solid, the chip formation and the formation of the groove, the squeeze-out behavior of the fluid in the contact zone, the local temperature and the energy balance of the system, the adsorption of fluid particles on the solid surfaces, as well as the formation of a tribofilm. Systematic studies were carried out for elucidating the influence of the wetting behavior, the influence of the molecular architecture of the lubricant, and the influence of the lubrication gap height on the contact process. As expected, the presence of a fluid lubricant reduces the temperature in the vicinity of the contact zone. The presence of the lubricant is, moreover, found to have a significant influence on the friction and on the energy balance of the process. The presence of a lubricant reduces the coefficient of friction compared to a dry case in the starting phase of a contact process, while lubricant molecules remain in the contact zone between the two solid bodies. This is a result of an increased normal and slightly decreased tangential force in the starting phase. When the fluid molecules are squeezed out with ongoing contact time and the contact zone is essentially dry, the coefficient of friction is increased by the presence of a fluid compared to a dry case. This is attributed to an imprinting of individual fluid particles into the solid surface, which is energetically unfavorable. By studying the contact process in a wide range of gap height, the entire range of the Stribeck curve is obtained from the molecular simulations. Thereby, the three main lubrication regimes of the Stribeck curve and their transition regions are covered, namely boundary lubrication (significant elastic and plastic deformation of the substrate), mixed lubrication (adsorbed fluid layers dominate the process), and hydrodynamic lubrication (shear flow is set up between the surface and the asperity). The atomistic effects in the different lubrication regimes are elucidated. Notably, the formation of a tribofilm is observed, in which lubricant molecules are immersed into the metal surface. The formation of a tribofilm is found to have important consequences for the contact process. The work done by the relative motion is found to mainly dissipate and thereby heat up the system. Only a minor part of the work causes plastic deformation. Finally, the assumptions, simplifications, and approximations applied in the simulations are critically discussed, which highlights possible future work.

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Section: Computational Tribology On the Atomistic Levelmentioning

confidence: 99%

Influence of Lubrication on Tribological Nanoscopic Contact Processes

Stephan

2024

Preprint

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“…Under the high temperature of the friction surface, these nanoparticles can easily melt or sinter in the microcracks in the contact zone, forming ordered nanoparticles and closely bonding with the friction surface [128]. Yi et al [140] used a molecular dynamics approach to construct rough surfaces and multilevel dimpled structures to simulate oil-poor lubrication before oil film rupture, and the simulation results showed that multilayered MoS 2 acted as a load-bearing agent at light loads or low speeds and went into the grooves to repair the surfaces at heavy loads or high speeds. Yi et al [141] used a solvent/hydrothermal method to prepare MoS 2 particles in three morphologies: flower-like, microspheres, and nanosheets.…”

Section: Other Mechanismsmentioning

confidence: 99%

MoS2 Nanomaterials as Lubricant Additives: A Review

Lu,

Lin,

Cao

et al. 2023

Lubricants

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Improving the lubricating properties of base oils through additives is a crucial objective of tribological research, as it helps to reduce friction and wear of materials. Molybdenum disulfide (MoS2) is a 2D nanomaterial with excellent tribological properties that is often used as a lubricant additive. Several studies have been conducted on the preparation and utilization of MoS2 and its nanocomposites as lubricant additives. This paper reviews the research progress on MoS2 nanomaterials as lubricant additives. It firstly introduces various synthesis methods of MoS2 nanomaterials while focusing on the preparation of nano-MoS2 as lubricant additives. It then summarizes the dispersion stability of nano-MoS2 in lubricating oils which has been paid extensive attention. Moreover, this paper reviews and discusses the tribological properties of nano-MoS2 and its various composites as lubricant additives. The possible anti-wear and friction reduction mechanisms of nano-MoS2 and its composites are also discussed. Finally, this paper presents the challenges faced by nano-MoS2 additives in the field of lubrication and the prospects for future research in view of previous studies.

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Sliding Friction in Liquid Environments at the Nanoscale

Berkovich,

An,

Gnecco

2024

NanoScience and Technology

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Frictional properties of MoS₂ on a multi-level rough wall under starved lubrication

Abstract: Owing to nano-MoS2’s excellent anti-friction and anti-wear properties, nano-MoS2, which can be acted as a nano-additive in lubricating oil or solid lubricant, is believed to have great potential in the...

Cited by 5 publications

References 37 publications

Influence of Lubrication on Tribological Nanoscopic Contact Processes

Influence of Lubrication on Tribological Nanoscopic Contact Processes

MoS2 Nanomaterials as Lubricant Additives: A Review

Sliding Friction in Liquid Environments at the Nanoscale

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Frictional properties of MoS2 on a multi-level rough wall under starved lubrication

Abstract: Owing to nano-MoS2’s excellent anti-friction and anti-wear properties, nano-MoS2, which can be acted as a nano-additive in lubricating oil or solid lubricant, is believed to have great potential in the...

Cited by 5 publications

References 37 publications

Influence of Lubrication on Tribological Nanoscopic Contact Processes

Influence of Lubrication on Tribological Nanoscopic Contact Processes

MoS2 Nanomaterials as Lubricant Additives: A Review

Sliding Friction in Liquid Environments at the Nanoscale

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Product

Resources

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Frictional properties of MoS₂ on a multi-level rough wall under starved lubrication