This study discusses the mechanism by which Ti₃C₂T_x MXene enhances the wear/corrosion resistance of polyimide (PI) coatings from the perspectives of interface interaction, bonding and filler structure. Despite the excellent performance of Ti₃C₂T_x MXene, its challenges in forming strong interface and strong bonding in PI limit its protection efficiency. To address this, we innovatively prepared amino-functionalized Ti₃C₂T_x nanoflowers (Ti₃C₂T_x@PEI) and uniformly dispersed them in the PI matrix as an enhancer. The results show that Ti₃C₂T_x@PEI achieves optimal protection of PI (the PI composite coating containing Ti₃C₂T_x@PEI nanoflowers (PMX–PI)). Under high loading, the wear rate of the PMX–PI composite coating is only 6.23×10⁻⁵ mm³·N⁻¹·m⁻¹. After the 4-week immersion test, the highest low-frequency impedance modulus (|Z|_0.01Hz) value of 3.73×10⁷ Ω·cm², approximately two orders of magnitude higher than that of the PI, is maintained. The coating resistance (R_c) is 1.81×10⁶ Ω·cm², which is approximately 2.2 times greater than that of PI (8.07×10⁵ Ω·cm²). According to Materials Studio (MS) calculations, Ti₃C₂T_x@PEI has the highest affinity for the PI precursor (polyamic acid, PAA), with an interaction energy of −21.41 kcal·mol⁻¹. Additionally, the –NH₂ groups in Ti₃C₂T_x@PEI are effectively utilized to form –CON– groups through dehydration condensation with –COOH groups in PAA at high temperature. These strong interactions and bonds promote uniform dispersion, filling the structural defects of PI.

While amorphous carbon-based films are recognized for their efficacy in mitigating fretting wear, owing to the fact that tribopairs demonstrate divergent tribological responses under different fretting states, it remains essential to explore their friction-mitigation mechanisms across distinct fretting regimes and elucidate the evolutionary patterns of these regimes. This effort is critical to gaining a thorough and systematic insights into the fretting characteristics of amorphous carbon-based films. The running conditions fretting map was constructed via friction force-displacement curves, and the evolutionary relationship between the two fretting regimes was explored. Additionally, the wear mechanisms and friction-mitigation mechanisms under these two regimes were systematically investigated via advanced characterization techniques, including FIB-TEM, SEM, Raman spectroscopy, and XPS. Results show that increasing normal load shifts fretting regime toward partial slip regime, leading to a decreased friction coefficient and increased wear volume, dissipated energy, and tangential stiffness. Increasing displacement amplitude drives the fretting regime to evolve toward the slip regime, resulting in increased friction coefficient, wear volume, and dissipated energy, along with decreased tangential stiffness. Notably, an amorphous-nanocrystalline composite structure, in which iron oxides are encapsulated by graphitized carbon film, forms on the surface of counterpart balls in the slip regime. This structure exerts a pivotal effect on mitigating the friction coefficient and fretting wear. Furthermore, this work advances the fundamental understanding of the mechanisms governing the tangential fretting wear of DLC films, and offers valuable design guidance and a robust theoretical basis for alleviating fretting damage.

Improving the oil retention capacity while maintaining mechanical stability remains pivotal in the development of advanced oil-containing composite coatings. In this study, oxidized graphene-functionalized composite lithium soap fibers (CLF/PG), which exhibit high oil affinity, were utilized to form a hydrogen bond network with epoxy resin (EP), constructing an effective oil retention network. By integrating dynamic micellar loading–desorption technology with a dual-spray gun system, we achieved uniform dispersion of oil microdroplets (G2825) within the oil retention network, ultimately resulting in a composite coating (C-G/EP). Notably, the 1.0 wt% C-G/EP sample exhibited a wear rate of only 0.212×10⁻⁵ mm³/(N·m) after 80,000 friction cycles—a remarkable 98.14% reduction compared with that of the EP sample. Concurrently, the system maintained a stable average friction coefficient of ~0.031. Molecular dynamics simulations revealed that oil microdroplet integration within the hydrogen-bonded network simultaneously increased the bulk and shear moduli while reducing the Young’s modulus. The modulus reconfiguration facilitates a transition from rigid contact to microelastic deformation behavior at friction interfaces. This deformation behavior, synergizing with the load-bearing abilities of composite lithium soap fibers (CLFs) and aminated graphene oxide (PG), enhances the strength of the lubrication film, thereby shifting the lubrication state of C-G/EP from boundary lubrication to elastohydrodynamic lubrication. This work provides fundamental insights for designing high-performance self-lubricating coatings based on liquid fillers.

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.