To achieve reliable self-lubrication of machine components working under conditions of extreme low temperature, a carbon-based nanocomposite coating co-doped with molybdenum disulfide (MoS₂) and silver (Ag) was fabricated by high-power pulsed magnetron sputtering (HiPIMS). The microstructure, mechanical properties and tribological behaviors over wide temperature range were investigated. The results show the hardness and elastic modulus of DLC/MoS₂-Ag coating increase as the temperature decreases. At room temperature (RT) to -40°C, the coating demonstrates stable superlubricity in N₂ atmosphere with a low the coefficient of friction (COF) of 0.0075. This superlubricity is primarily attributed to the graphitization induced by friction and the “ordered Ag nanoparticle array” formed within the transfer film. As the temperature decreases from -40°C to -120°C, COF gradually increases to 0.0865, and the wear gradually increases. This degradation is closely related to the suppressed graphitization of the DLC coating and the deterioration of the low-friction “ordered Ag nanoparticle array” structure at interface. When the temperature is further reduced to -160°C, the graphitization of the coating is significantly inhibited, and the cryogenic mechanical performance is deteriorated, resulting in excessive consumption of Ag on the surface of the coating, which makes it difficult to maintain the special structure of the ordered Ag nanoparticle array at the friction interface. Consequently, the self-lubrication capability of the interface is further reduced, however the coating still presents COF below 0.1. These test results show that the DLC/MoS₂-Ag composite coating designed in the present study can give ultra-low COF in a wide temperature range, which provides valuable insights into the design of carbon-based coatings in extreme low temperature conditions.

Rolling contact fatigue (RCF) failures in critical components such as precision gears and high-performance bearings have become increasingly prominent under demanding conditions. Conventional lubricant additives struggle to reduce friction simultaneously, resist wear, and repair dynamic micropitting. To address this challenge, a composite material of ionic liquid-functionalized magnesium silicate hydroxide (MSH) ([DDP][TOA]/MSH (DDP = dialkyl dithiophosphate, TOA = trioctylamine)) was synthesized using hydrothermal synthesis and noncovalent modification. This composite exhibited remarkable dispersion stability and copper corrosion inhibition, as well as superior tribological properties, including friction reduction, wear mitigation, and micropitting repair during rolling–sliding contact. Tribological evaluations revealed that 1.0 wt% [DDP][TOA]/MSH reduced the friction coefficient by 17.2% and the wear volume by 52.5%, demonstrating unprecedented load-bearing capacity and frequency adaptability. Notably, under rolling–sliding contact fatigue conditions, commercial gear oil exacerbated micro-pitting damage continuously, whereas the composite material repaired damage, with a repair efficiency of 72.0%. Surface characterization reveals a three-stage mechanism for the dynamic repair of worn metal surfaces: (1) micro-asperities are removed through mechanical grinding, (2) micro-cracks are filled via tribochemical deposition of FeS/phosphate phases, and (3) a hybrid a-SiC/a-SiO_x repair layer is formed with improved mechanical strength, effectively preventing fatigue wear propagation. This work demonstrates the synergistic effect of ionic liquids and layered silicate additives on micropitting repair under rolling contact fatigue, expanding the application of MSH in the field of commercial lubricant additives.

In this work, the idea of water lubrication enhanced by a small quantity of oil was tested for the first time in a rubber journal bearing. A small quantity of silicone oil was supplied to an eight-groove rubber bearing through a small nozzle, aiming to improve the lubrication of the bearings under short-time severe working conditions. Results demonstrated that the addition of small-quantity silicon oil can significantly reduce friction, with the coefficient of friction (COF) at certain speeds being lower than that achieved with either pure water or pure oil. If the oil was given under frequent and small-quantity supply, smaller time interval of oil supply has little impact on friction reduction. Moreover, a simple method based on the Stribeck curve was proposed to roughly predict the COF reduction of water-lubricated journal bearings with small-quantity oil supply at low speeds. Additionally, computational fluid dynamics (CFD) simulations provided insights into the migration/diffusion of injected oil within the bearing, revealing a correlation between oil side leakage and COF.

The effects of tuned surface wettability on oil film formation in a hydrodynamically lubricated contact with a limited lubricant supply (LLS) were explored in this study. Using a slider-on-disc lubricating film test rig, the oil film thickness was measured for three surface wettability configurations: the original disc surface and original slider side surface (OD & OS), the anti-fingerprint (AF)-coated disc surface and original slider side surface (AFD & OS), and the AF-coated disc surface and the AF-coated slider side surface (AFD & AFS). The results indicate that the AFD & AFS combination maintains the largest oil film thickness. This enhanced performance is due to the oil’s nonwetting behavior on the AFD & AFS surfaces, particularly the discontinuous oil droplet/strip by dewetting, which promotes more lubricant supply at the slider inlet. Moreover, the oil accumulates at the inlet in the form of a convex reservoir so that positive Laplace pressure is generated, which effectively bears part of the load, and the film thickness increases.

Effective oil replenishment to the lubrication track of a running bearing is crucial to its sustainable operation. Reliable practical solutions are rare despite numerous theoretical studies were conducted in the last few decades. This paper proposes the use of surface effect, wettability gradient, to achieve the goal. This method is simple and can be nicely implemented using femtosecond laser ablation. A periodic comb-tooth-shaped pattern with anisotropic wetting capability is devised and its effect on the anisotropic spreading behaviour of an oil droplet is studied. Results show that the comb-tooth-shaped pattern enables the rearrangement of oil distribution, thereby escalating oil replenishment to the lubrication track. The effect is due to the unbalanced interfacial force created by the surface pattern. The influence of the shape and the pitch of teeth, which are the two governing factors, on oil transport is also reported. The effects of the newly devised surface pattern on lubrication are experimentally evaluated under the conditions of limited lubricant supply. These results are promising, demonstrating the reduction in bearing friction and the increase in lubricating film thickness.