Efficient cooperative lubrication can be achieved via the introduction of core‒shell structure lubricant additives with hard core and soft shell, for obtaining the expected anti-wear performance from the structural changes in the friction process. In this study, C@Ag microspheres with a core‒shell structure were prepared by the redox method with carbon spheres as the core and Ag nanoparticles as the shell. Their tribological behaviors as base oil (G1830) additive with different concentrations were investigated in detail. Compared with base oil, the addition of C@Ag particles at 0.5 wt% can reduce the coefficient of friction (COF) and wear volume (Wv) up to 15.5% and 88%, respectively. More importantly, C@Ag particles provide superior lubrication performance to single additive (like carbon sphere (CS) and Ag nanoparticle). C@Ag core‒shell particles contribute to the formation of tribo-film by melt bonding of flexible Ag and carbon sphere (CS) toward excellent self-repair performance and high-efficiency lubrication. Hence, core‒shell structural nanoparticles with hard-core and soft-shell hold bright future for high-performance lubrication application.

The bonded MoS₂ solid lubricant coating is an effective measure to mitigate the fretting wear of AISI 1045 steel. In this work, the amino functionalized MoS₂ was protonated with acetic acid to make the MoS₂ positively charged. The directional arrangement of protonated MoS₂ in the coating was achieved by electrophoretic deposition under the electric field force. The bonded directionally aligned MoS₂ solid lubricant coating showed high adaptability to various loads and excellent lubrication performance under all three working conditions. At a load of 10 N, the friction coefficient and wear volume of the coating with 5 wt% protonated MoS₂ decreased by 20.0% and 37.2% compared to the pure epoxy coating, respectively, and by 0.07% and 16.8% than the randomly arranged MoS₂ sample, respectively. The remarkable lubricating properties of MoS₂ with directional alignment were attributed to its effective load-bearing and mechanical support, barrier effect on longitudinal extension of cracks, and the formation of a continuous and uniform transfer film.

By simply switching the electrical circuit installed on steel/steel contact, the tribological behaviors of nanofluids (NFs) can be regulated in real time, thereby achieving the desired performance of friction reduction and wear resistance. Herein, solvent-free carbon spherical nanofluids (C-NFs) were successfully prepared for intelligent lubrication regulation. C-NFs with excellent lubrication performance can immediately reduce the coefficient of friction (COF) despite applying a weak electric potential (1.5 V). Moreover, polyethylene glycol 400 (PEG400) containing 5.0 wt% C-NFs remained responsive to electrical stimulation under the intermittent voltage application with an average coefficient of friction (ACOF) reduction of 20.8% over PEG400. Such intelligent lubrication regulation of C-NFs under an external electric field (EEF) mainly depends on the orderly arranged double-electric adsorption film of ion canopy-adsorbed carbon spheres (CSs). The intermittent electrical application can continuously reinforce the adsorption film and its durability for real-time controlling the sliding interfaces. Electrical-stimulation-responsive intelligent lubricants provide a new technical support for realizing intelligent stepless control of devices.

The few-layer Ti₃C₂T_x/MoS₂ heterostructure was successfully prepared via vertically growing of MoS₂ nanosheets on the few-layer Ti₃C₂T_x matrix using hydrothermal method. The tribological properties as additive in mineral oil (150N) were evaluated in detail. The 0.3 wt% of few-layer Ti₃C₂T_x/MoS₂ heterostructure addition amount can reduce the friction and wear of 150N by 39% and 85%, respectively. Moreover, the enhancement effect of few-layer Ti₃C₂T_x/MoS₂ on tribological properties of 150N is superior to that of few-layer Ti₃C₂T_x, MoS₂ nanosheets, and their mechanical mixture. Based on the characterization and analysis of wear debris and wear track, such excellent tribological properties of the few-layer Ti₃C₂T_x/MoS₂ heterostructure derive from its structural advantage toward good dispersion, the synergistic lubrication of Ti₃C₂T_x and MoS₂ nanosheets during the rubbing process, and the formation of tribo-film.

Deep eutectic solvents (DESs) have been considered as novel and economic alternatives to traditional lubricants because of their similar physicochemical performance. In this study, choline chloride (ChCl) DESs were successfully synthesized via hydrogen-bonding networks of urea and thiourea as the hydrogen bond donors (HBDs). The as-synthesized ChCl–urea and ChCl–thiourea DESs had excellent thermal stability and displayed good lubrication between steel/steel tribo-pairs. The friction coefficient and wear rate of ChCl– thiourea DES were 50.1% and 80.6%, respectively, lower than those of ChCl–urea DES for GCr15/45 steel tribo-pairs. However, for GCr15/Q45 steel, ChCl–urea DES decreased the wear rate by 85.0% in comparison to ChCl–thiourea DES. Under ChCl–thiourea DES lubrication, the tribo-chemical reaction film composed of FeS formed at the interfaces and contributed to low friction and wear. However, under high von Mises stress, the film could not be stably retained and serious wear was obtained through direct contact of friction pairs. This illustrated that the evolution of the tribo-chemical reaction film was responsible for the anti-friction and anti-wear properties of the DESs.

Thickener formulation plays a significant role in the performance characteristics of grease. The polyurea greases (PUGs) were synthesized using mineral oil (500SN) as the base oil, and by regulating the reaction of diphenylmethane diisocyanate (MDI) and different organic amines. The as-prepared PUGs from the reaction of MDI and cyclohexylamine/p-toluidine exhibit the optimum physicochemical and friction-wear properties, confirming that the regulation of thickener formulation can improve the performance characteristics of grease, including friction reduction, wear, corrosion resistance, and load-carrying capacity. The anti-corrosion and lubrication properties of as-prepared PUGs depend on good sealing functions and a boundary lubrication film (synergy of grease-film and tribo-chemical reaction film), as well as their chemical components and structure.

In this study, lithium complex grease (LCG) and polyurea grease (PUG) were synthesized using mineral oil (500SN) and polyalphaolefin (PAO40) as base oil, adsorbed onto lithium complex soap and polyurea as thickeners, respectively. The effects of grease formulation (thickener and base oil with different amounts (80, 85, and 90 wt%) on the corrosion resistance and lubrication function were investigated in detail. The results have verified that the as-prepared greases have good anti-corrosion ability, ascribed to good salt-spray resistance and sealing function. Furthermore, the increase in the amount of base oil reduces the friction of the contact interface to some extent, whereas the wear resistance of these greases is not consistent with the friction reduction, because the thickener has a significant influence on the tribological property of greases, especially load-carrying capacity. PUG displays better physicochemical performance and lubrication function than LCG under the same conditions, mainly depending on the component/structure of polyurea thickener. The polyurea grease with 90 wt% PAO displays the best wear resistance owing to the synergistic lubrication of grease-film and tribochemical film, composed of Fe₂O₃, FeO(OH), and nitrogen oxide.

In this study, spherical and mesoporous NiAl particles (abbreviated as sNiAl and mNiAl) were introduced as lubricant additives into two alkyl-imidazolium ionic liquids (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate (LB104) and 1-butyl-3-methyl imidazolium hexafluorophosphate (LP104)) to explore their tribological properties. The sNiAl and mNiAl particles were modified in-situ by anion and cation moieties of ILs through chemical interaction, thereby enhancing their dispersibility and stability in ILs. The mNiAl particles have better dispersibility than the sNiAl ones in ILs because of high specific surface area. LP104-modified sNiAl particles show better friction reduction and wear resistance, mainly relying on the synergy of the hybrid lubricant. These particles form a protective layer that prevents friction pairs from straight asperity contact and improves the tribological behaviors.