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To improve the tribological properties of polyurethane (PU) based water-lubricated bearings specifically under severe conditions, expanded graphite/paraffin (EG/paraffin) is synthesized as self-lubricating additives and incorporated into the polyurethane matrix. The tribological performance of the PU-EG/paraffin composites at dry and water-lubricated conditions is investigated systemically. Results show that the friction coefficient of PU-EG/paraffin composites can reach a minimum value of 0.18 and 0.08 under dry and water lubricating conditions, respectively, with a reduction of 77% and 62% compared to that of pure PU. Meanwhile, the wear rate of these composites also exhibits a significant decrease under both conditions. The wear surface morphology indicates that a lubricating film can be formed by paraffin or paraffin-water emulsion between the friction pairs, thereby significantly enhancing the lubrication state under dry and water lubricating conditions, respectively. The present work puts forward a practical and effective approach for manufacturing self-lubricating water-lubricated bearing materials.

In response to the persistent challenge of optimizing the tribological performance of engineered coatings without compromising material hardness, this study investigates the potential of medium-entropy CrCoNiCu alloy films. Fabricated via sputtering and subsequently aged at 200 °C for 24 h, these films are examined for their mechanical and tribological behaviors through nanoindentation and reciprocal sliding wear tests. The primary result reveals that the sputtering fabrication yields a single face-centered cubic phase enriched with stacking faults and twins due to a vapor quenching and an increase in defective nuclei formation. The aging treatment uniquely facilitates the formation of Cu-rich phases, featuring repetitive plate-like structures along twin boundaries, by altering diffusion pathways to enhance diffusivity at the applied low temperature. Remarkably, this process not only increases the hardness of the films by 1.5 GPa but also leads to significant improvements in their tribological performance, with reductions in friction coefficients and wear volumes by 12.1% and 90.1%, respectively. The tribological properties originate with the synergistic effects of precipitation hardening and the lubricating layer inducing the reduction of abrasive wear and inhibition of direct contact between sliding surfaces. These findings illuminate that the CrCoNiCu alloy exhibits an exceptional capacity for superior wear resistance at soft metals, offering a compelling strategy to navigate the traditional trade-off between wear rate and hardness in the design of advanced engineering materials.

The primary objective of this research is to investigate the structure and tribological properties of NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer films in a wide temperature range (RT-1000 °C). The bilayer films were prepared by pulsed laser deposition (PLD) technology, so as to provide the theoretical basis and experimental guidance for the study of the synergistic lubricating effect of Mo and V bimetallic lubricating oxides. The NiCr–Mo–Ag–O composite target was fabricated by the hot-press sintering technique. Subsequently, a NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer film was deposited on Inconel 718 by pulsed laser deposition (PLD). The tribological properties of the film were evaluated by HRT-1000 high-temperature ball-on-disc configuration at RT-1000 °C. The obtained results reveal that the NiCr–Mo–Ag–O target is marked by a compact structure and homogeneous composition. Furthermore, the composite film exhibits a smooth surface and dense structure, comprised of polycrystalline and amorphous phases. The measured hardness and elastic modulus of the film approximated 4.9 GPa and 153.5 GPa, respectively. Additionally, the lowest friction coefficient of the film is about 0.28 at 800 °C. Upon reaching this temperature, the cooperative lubrication resulting from NiMoO4, Ag2Mo2O7, and AgVO3 contributed effectively towards reducing the film's friction coefficient.

The evolution of pearlite into an amorphous wrapped nanolamellar heterostructure (AWNH) within the tribolayer is an important process for the formation and stabilization of a nanocomposite self-lubricating surface. Here, experimental characterizations were performed to show that an AWNH was an intermediate product of transformation of pearlite to oxide nanoparticles and played a supporting role as a self-lubricating layer of the substrate. Furthermore, the molecular dynamics simulation method was used to analyze the wear properties and load-bearing capacities of four different microstructures to reveal the unique AWNH deformation mechanism and its effect on the self-lubrication behavior. The results showed that the AWNH exhibited a low friction and good wear resistance, which could be ascribed to its high hardness, high plasticity, and outstanding interface deformation coordination ability. The shear bands were restricted by the nanolamellar structure, and the shear transition zone that formed at the interfaces caused the plastic deformation to be uniformly distributed, which provided favorable conditions for supporting the self-lubricating layer. The results of this study provide theoretical guidance for analyzing the deformation mechanisms and tribological behaviors of AWNHs and help to optimize self-lubricating material design.

The self-lubricating mechanism of Cu–Pb bearing alloy is discussed by molecular dynamics (MD). MD friction tests are conducted on the pure Cu and Cu–Pb models. The Pb-rich secondary phases (PSPs) melt due to the frictional heat. The solid–liquid phase transition of Pb is characterized by the radial distribution function (RDF) and the potential energy. An obvious drop of motion resistance of the abrasive debris is observed in Cu–Pb alloy once the debris moves close to the soft PSP which protect the matrix from abrasion by embedding the debris and promoting the formation of a liquid lubricant film. The synchrotron radiation technology is employed to in-situ observe the phase transition of Pb, and the MD results match the experimental results well.

A novel thermoplastic polyurethane (TPU) matrix composite was combined with tetra-needle zinc oxide whisker (T-ZnOw) and molybdenum disulfide (MoS2) particles. Frictional vibration experiments were conducted to study the effect of T-ZnOw and MoS2 particles on frictional vibration behaviors. The tribological properties and vibration behaviors of TPU composites were synthetically analyzed to reveal the effects of T-ZnOw and MoS2 on the friction excitation force and vibration reduction properties. The results showed that T-ZnOw enhanced anti-deformation property, and MoS2 weakened the friction excitation force in the friction process, which resulted in a lower coefficient of friction (COF) with a small amplitude, and eliminated the high-frequency vibration amplitude. In addition, the particle composition of 6% T-ZnOw and 9% MoS2 was controlled to obtain a low COF and the best vibration reduction properties. The knowledge obtained herein contributes to the understanding of the synergistic effects of T-ZnOw and MoS2 on COF and vibration reduction behaviors, and the development of a water-lubricated TPU composite stern tube bearing with low COF and good vibration reduction properties.

Lignum vitae was widely applied in water-lubricated bearing because of its green, pollution-free, excellent mechanical, and self-lubricating properties. The slow growth cycle is difficult to meet the bearing's rapid development. Lignum vitae chips were used to modify thermoplastic polyurethane (TPU) to extend its good self-lubricating properties and improve tribological behaviors. The results showed that lignum vitae improve TPU's shore hardness, elastic modulus, and elongation, but at the slight cost of tensile strength and thermal stability. Besides, lignum vitae chips endowed TPU with good hydrophilicity and water absorption properties, which conduced to form effective lubricating film and reduced COF behaviors. TPU with 6% lignum vitae chips had the best COF reduction and wear resistance. But excessive lignum vitae chips weakened elastic modulus and elongation to increase COF behaviors and wear process. The outcome obtained herein would provide strong theoretical guidance for developing novel green and sustainable composites with excellent tribological properties.

This paper reports on the fabrication and tribological performances of surface textured plasma electrolytic oxidized (PEO) coatings containing polytetrafluoroethylene (PTFE) on aluminum alloy (PEO/PTFE). The ordered arrays of circular dimples were created on PEO ceramic coating surface by laser surface texturing and vacuum penetration of nanosized-PTFE was followed in vacuum chamber. The tribological properties of PEO/PTFE and textured PEO/PTFE coatings were evaluated at load of 5–25 N using a UMT-4 tribometer under dry condition. The results shown that surface texturing can effectively reduce the friction coefficient of contact interface for 72,000 cycles at 5 N and greatly improve the bearing capacity of PEO/PTFE coating, because of the constantly compensation of lubricating PTFE film in the wear track. This study established a new approach to fabricate self-lubricating ceramic PEO coating on aluminum alloys.

Here, new insight into amorphization induced by deformation at ferrite-cementite nanointerfaces in a tribolayer is put forward, and an atomistic investigation into interfacial effects on amorphization is carried out using molecular dynamics (MD) simulations and spherical aberration-corrected high-resolution TEM (HRTEM) characterization. Nanoamorphous particles mix with oxide particles attached to the wear surface, which provide a lubrication state during dry sliding friction of pearlite steels. HRTEM images and energy-dispersive X-ray spectroscopy (EDS) maps show alternating ferrite-amorphous-ferrite lamellar features in the tribolayer. MD simulation results show that ferrite-cementite nanointerfaces with the Bagaryatskii orientation play important roles in the above amorphization, which can be exposited by the deformation response between the ferrite and cementite being inconsistent. A high density of dislocation defects destroys the ferrite-cementite interfaces to create an amorphous nucleation region, and after nucleation, the amorphization will expand into the cementite. This study lays the theoretical basis for revealing the mechanism of cementite amorphization in the tribolayer and will provide new ideas for designing and manufacturing amorphous self-lubricating films or solid materials.