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Friction and wear of motion components operating under harsh lubrication conditions are key aspects that must be considered in vast numbers of applications. In the present work, graphene oxide (GO) functionalized in-situ with ionic liquid (IL) were uniformly dispersed into epoxy (EP) via a two-phase extraction route. In comparison to as-exfoliated GO, GO functionalized with IL (GO-IL) showed significantly improved dispersibility in EP matrix. It was disclosed that the addition of only low-loading GO-IL significantly reduced the friction and wear of EP over whole lubrication regimes, whereas as-exfoliated GO nanosheets played a positive role just under the moderate lubrication conditions. In particular, obvious synergy between the IL and GO was identified when sliding took place under harsh rubbing conditions. Comprehensive interface characterizations provided direct evidence that a nanostructured tribofilm comprising GO nanosheets, IL chemical groups and EP matrix was established. It was surmised that tribofilm growth was constantly fed by molecular species released from GO-IL reinforced EP, while GO digested within the tribofilm enhanced its robustness and improved the boundary lubrication capability. This work opens up new opportunities for formulating high-performance polymer composites for a wide range of applications subjected to harsh boundary lubrication conditions. [ABSTRACT FROM AUTHOR]

In response to the challenges posed by friction and wear of tribo-components exposed to boundary and mixed lubrication conditions, there is increasing interest in the development of polymer-based, self-lubricating composites. This investigation addressed the effect of various fillers (i.e. short carbon fibers (SCF), short glass fibers (SGF), ZnS sub-micrometer particles and combinations of respective fibers with ZnS particles), on the friction and wear of polyimide (PI) when lubricated by poly-alpha-olefins (PAO). A sliding plate-on-ring geometry, using GCr15 steel rings, was used. It was demonstrated that the reinforcing fibers greatly improved the composites’ wear resistance. SGF was observed to be more effective than SCF in respect to friction- and wear-reduction. Moreover, an obvious synergism between SGF and ZnS was identified. The hybrid composite ZnS/SGF/PI exhibited excellent tribological performance under oil lubrication. With respect to the hybrid formulation, the glass fibers imparted their high abrasion resistance to the composite; while ZnS led to complex tribo-chemical reactions. A stable tribofilm consisting of transferred materials and various tribo-chemical products improved the boundary lubrication capability of the sliding system. [ABSTRACT FROM AUTHOR]

Antigorite is a Mg-rich 1:1 trioctahedral-structured layered silicate mineral. In recent decades, many studies have been devoted to investigating the tribological performance and application of antigorite as lubrication materials. This article provides an overview of the mineralogy, thermal decomposition and surface modifications of antigorite powders, as well as the recent advancement that has been achieved in using antigorite to reduce friction and wear of friction pairs. The tribological performance of antigorite powders and its calcined product in different lubricating media, such as oil, grease and solid composites have been comprehensively reviewed. The physico-chemical characteristics of surface layers of the friction pairs are discussed. Applications and mechanisms of lubricity and anti-wear of antigorite are highlighted. [ABSTRACT FROM AUTHOR]

Tribological behaviors of carbon fibers (CF) reinforced poly-ether-ether-ketone (PEEK) composites are investigated at low speeds ranging from 0.01 to 0.2 m/s under pressures varying from 1 to 30 MPa. Nano-Bi 2 O 3 , nano-SiO 2 and conventional solid lubricants (graphite and polytetrafluoroethylene) are further added into CF-reinforced PEEK, respectively. It is demonstrated that a small load and relatively high speed are favorable for the wear-reduction role of nano-Bi 2 O 3 , while the positive role of nano-SiO 2 is pronounced at a high load and speed. Friction and wear-reduction roles of the solid lubricants are the most significant at low load and low speed. It turns out that functionalities of the fillers are closely associated with their roles in tribofilm growth governed by complex physical and chemical actions. • Tribological mechanisms of PEEK composites at relatively low speeds were studied. • Nano-Bi 2 O 3 reduces wear of CF/PEEK at speeds higher than 0.05 m/s under 1 MPa. • Nano-SiO 2 enhances wear resistance of CF/PEEK at a high load and 0.1 m/s. • Graphite/PTFE plays an excellent lubrication role at the low speed range studied. • Tribological performance of the materials is closely related to tribofilm growth. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs), and MWCNTs/zirconia nanoparticles (nano-ZrO 2) hybrids were compounded into a formulated non-asbestos brake material of phenolic binder, respectively. It is demonstrated that even low-loading above nanofillers switching virtually the original brake material to an extremely wear-resistant self-lubricating material. More interestingly, the addition of MWCNTs/nano-ZrO 2 hybrids leads to formation of a double-deck tribofilm yielding extraordinarily low friction and wear. First-principles calculations demonstrate that O atoms from air ambience break carbon-carbon backbones of CNTs, facilitating them to convert into graphitic nanograins. Our work provides direct evidence that graphitic nanograins and nano-ZrO 2 are digested within the beneath layer of the tribofilm, whilst chelation of polymer chains radicals with nano-ZrO 2 expedites formation of a carbon-based lubricous top layer. The present work puts forward a new strategy for endowing numerous mechanical motion systems with a robust self-lubrication characteristic via tuning tribofilms' nanostructures. Growth of a double-deck tribofilm yielding ultra-low friction and wear. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Structural evolution and mechanical properties of polyurethane/epoxy interpenetration networks (PU/EP IPNs) as a function of PU content were comprehensively studied. In particular, tribological behaviors of the IPNs were investigated in water medium while varying lubrication regimes. Our results demonstrate that microstructures of PU/EP IPNs are closely dependent on stoichiometric proportions of their components. It is impressive that unlike conventionally modified polymers, blending 30 wt% PU into EP leads to simultaneous improvement in modulus, strength and ductility. Especially for sliding subjected to boundary lubrication, IPNs exhibited strikingly enhanced tribological performance when compared to neat EP and PU. Our work indicates that IPNs have a high application potential as tribo-materials exposed to water lubrication. Graphical abstract Image 1 Highlights • Structure and mechanical properties of PU/EP IPNs as a function of PU content were comprehensively studied. • Microstructures of PU/EP IPNs show close dependence on stoichiometric proportion of the components. • Blending 30% PU into EP improved simultaneously the modulus, tensile and impact strengths, ductility. • 3PU/7EP IPNs and 5PU/5EP IPNs exhibited excellent tribological performance in the boundary lubrication regime. • IPNs with regulated microstructures show a high potential for using as tribo-materials in water lubrication conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] The use of magnesite to prepare Mg–Al–CO3 LDH is novel. [•] The LDH used as lubricant additive were few reported. [•] LDH possesses an excellent property on reducing friction and wear of friction pair. [Copyright &y& Elsevier]

• The WS-CN lubricants were not only environmentally friendly during use, but also in the synthetic process. • On the premise of enough stability, mass production of WS-CN lubricants can be simply achieved. • In comparison to DI water, IL@WS-CN dispersion reduced the wear of neat EP by one order of magnitude. • Numerous CN nanograins distributed in the amorphous tribofilm enhanced the load-carrying capability and robustness. Development of high-performance water lubricants in replacement of conventional oil lubricants is of great significance for protecting our environment and ecology. Water-soluble graphitic carbon nitride (g-C 3 N 4) materials (WS-CN) were synthesized in situ by a one-pot green hydrothermal method in deionized (DI) water. For the first time, roles of as-synthesized WS-CN and ionic liquid (IL) grafted WS-CN (IL@WS-CN) as water lubricants on lubrication performance were investigated. Our results demonstrated that even rather small amount of WS-CN, e.g. 0.5 wt%, played an excellent lubrication effect. More interestingly, a striking synergy between IL and WS-CN on friction and wear-reduction was identified. In comparison to lubricating with DI water, IL@WS-CN dispersion reduced the wear by one order of magnitude and decreased the friction by up to 71%. Nanostructures of the friction interface were explored for shedding light on lubrication mechanisms. It was disclosed that WS-CN precipitating at the friction interface improved the load-carrying capability, and particularly triggered growth of a robust tribofilm, greatly improving the boundary lubrication effect. WS-CN opens up a new opportunity for developing mass-producible, low-costing and sufficient-stable water lubricants. [ABSTRACT FROM AUTHOR]

• Silica NFs exhibit excellent lubricity and remarkable stimuli responsiveness to an external electric field. • Lubricity and electrical responsiveness of the NFs are closely dependent on the corona structure. • A protective tribofilm grew in-situ when NFs are fed continuously onto the contact zone. Solvent-free ionic nanofluids (NFs) are promising smart lubrication materials due to their remarkable stimuli responsiveness to an external electric field. In this study, four kinds of silica (SiO 2) NFs with diverse corona molecule structures were successfully synthesized. Effects of NFs' structures on their physic-chemical properties and lubricity were investigated. In particular, nanostructures of the tribofilms were comprehensively characterized for shedding light on lubricating mechanisms of the NFs. Our results demonstrate that the newly synthesized NFs exhibit excellent lubrication performance and their lubricity displays remarkable electrical responsiveness. Applying even a rather low electrical potential, e.g. 1.5 V, gives rise to significant and immediate friction reduction. Moreover, lubricity and electrical responsiveness of the NFs are closely dependent on structures of the corona layers. Interestingly, our work provides direct evidence that feeding NFs onto the friction zone expedites growth of a robust tribofilm consisting mainly of SiO 2 nanoparticles and tribochemical products. This work opens up new opportunities for tuning structures and functionalities of boundary layers of numerous motion components by tailoring architectures of NFs and controlling the electrical stimuli. [ABSTRACT FROM AUTHOR]