Friction最新文献

Friction phenomena are strongly affected by interfacial mechanical and tribochemical effects, which involve major factors such as loads, sliding rates, sliding times, humidity, temperatures, and oxide films. For practical applications at different vacuum levels, friction mechanisms (adhesive wear, abrasive wear, fatigue wear, corrosive wear, and micromotor wear) are highly important for the development of advanced materials with desirable tribological properties to promote vacuum tribology. In this review, in combination with the current understanding of friction‒wear interactions, the tribological phenomena caused by changes in the surfaces of friction pairs that are highly dependent on complex conditions in different vacuum environments are analyzed and summarized. Subsequently, protection strategies for different structural materials are summarized. Finally, this work provides an outlook for designing advanced and sustainable protective materials under different vacuum conditions.

Recent studies have indicated that tribochemical reaction layers form on metal-on-metal-bearing surfaces, which may play a significant role in the performance and longevity of artificial joints. The purpose of this study was to determine the role of friction in the formation of tribofilms, and an in situ atomic force microscopy single-asperity sliding setup was used to perform in situ microscopic friction experiments to control the contact area and load. Time-of-flight secondary ion mass spectrometry and Raman spectroscopy were also employed to investigate changes in the composition and structure of the proteins at different sliding cycles. The results revealed that the proteins first unfolded under shear and then underwent chain breakage, dehydrogenation, and desulfurization over time as friction progressed. Finally, the carbonaceous fragments did not show graphitization trends under only shear stress.

High-temperature solid lubricant coatings with decent lubrication performance are essential in critical processes of metal forming and aerospace. However, their preparation is formidably challenging due to the harsh working conditions. Here, we successfully developed a solid lubricant coating via a facile and eco-friendly approach by casting a homogeneous mixture of molybdenum disulfide (MoS₂) and hexagonal boron nitride (h-BN) as lubricants, silicate as the binder, and water as the solvent onto a titanium alloy substrate. This solid lubricant coating exhibited excellent and stable tribological properties with a very low coefficient of friction (COF) of 0.080 at 1,000 °C, yet in an open-air atmosphere. This superior lubrication behavior is attributed to the synergistic effect between the base lubricants h-BN and MoS₂, contributing to the formation of a coating for both lubrication and lubricant protection against oxidation at 1,000 °C in an open-air environment. This work largely extends the operation temperature range of the crucial lubricant MoS₂ in an open-air atmosphere and further sheds valuable light on the design of high-temperature solid lubricants via the synergistic effect between base lubricants.

Reducing the coefficient of friction is a critical method for improving the service life and enhancing the efficiency of artificial implants. Maintaining a robust low-friction effect is essential for optimal artificial implant performance. This work utilizes the mechanism of the interaction between the interfacial charge and microviscosity to design a composite coating for titanium alloys modified with halloysite nanotubes/poly(vinylphosphonic acid) (PVPA). Compared with that of the pure PVPA coating, the coefficient of friction of the composite coating-polytetrafluoroethylene (PTFE) system stabilized at a low-friction state of approximately 0.008, with a 13.40% improvement in the load-bearing capacity. This low-friction state is maintained over a wide range of speeds and for extended periods. Furthermore, the study reveals that the electrical property differences between the inner and outer walls of halloysite nanotubes induce specific aggregation of anions and cations. These ions increase the microviscosity around the tube wall by forming hydrogen bonds with water molecules and attracting water molecules to form hydronium cations, contributing to the low-friction mechanism. The halloysite nanotube/PVPA composite coatings also enhance the toughness of the coating in the body fluid environment by stabilizing the crosslinked core region against perturbations from multivalent cations. The results provide a new approach for achieving low-friction composite polymer coatings with improved frictional properties in biotribology.

Based on the ordinary state-based peridynamics (OSB PD) theory, a 2.5-dimensional (2.5D) PD model for rail crack propagation in railway turnouts was proposed. First, a two-dimensional (2D) model for rail crack propagation in railway turnouts was constructed, with two types of 2.5D additional constraints for crack opening and cross section proposed on the basis of the 2D model. The 2.5D PD model for rail crack propagation in railway turnouts could thus be established. A fatigue crack propagation experiment was subsequently carried out on the U71Mn turnout rail material. The bond fatigue failure condition of the turnout rail material was established on the basis of the experimental results. Finally, the accuracy of the structural deformation and bond fatigue failure conditions was verified. The simulation results for rail crack propagation were compared with field observations and then analyzed in detail. These results show that the proposed 2.5D PD model can be used to accurately simulate the characteristics and rules for rail crack propagation in railway turnouts.

Carbon dots (CDs) are widely recognized for their superior adsorption and film-forming capabilities on metallic surfaces, making them effective as liquid lubricant additives and corrosion inhibitors. However, their applications in solid lubricating and organic anti-corrosion coatings have been less reported. In this study, nitrogen-doped CDs (N-CDs) with a polymer-carbon core hybrid structure are synthesized via a facile aldol condensation of acetaldehyde and urea. The incorporation of these N-CDs as additives into waterborne epoxy (WEP) coatings enhances interfacial compatibility, resulting in remarkable improvements in lubricating performance and corrosion resistance. Compared to the pure WEP coating, the N-CDs based nano-composite coating (WEP(PDMS)@N-CDs) demonstrates a dramatic reduction in the coefficient of friction from 0.760 to 0.049, representing a 93.6% decrease. Additionally, the WEP(PDMS)@N-CDs coating exhibits exceptional corrosion resistance, as evidenced by a stable low-frequency impedance modulus of │z│_{0.01 Hz}=3.5×10⁷ Ω cm². These improvements are primarily attributed to the abundant polymer branched chains on the N-CDs surface, which effectively increase the cross-linking density of the WEP polymer. The resulting WEP(PDMS)@N-CDs coating not only facilitates dynamic repair during friction but also enhances the barrier effect of the coating, leading to significantly improved anti-wear and corrosion resistance.

Current methods for assessing pavement skid resistance are based on spot or line sampling, neglecting the lateral skidding risk of vehicles derived from the uneven distribution of pavement friction coefficients. Through mechanical analysis, this study illustrates that vehicles are susceptible to lateral instability when the road surface exhibits unequal friction coefficients between the left and right wheel tracks. Based on this finding, vehicle dynamics simulations are conducted to evaluate longitudinal and lateral braking distances under varying speeds and friction coefficient distributions. It was found that when the friction coefficients are below 0.5, the risk is dominated by the longitudinal braking distance. Conversely, when there is a significant disparity in friction coefficients between the left and right wheel tracks (exceeding 0.2), the risk is predominantly associated with lateral skidding. Sensitivity analysis further examined the combined effects of friction disparities and driving speed, revealing that when speed exceeds 80 km/h, lateral skidding risk induced by uneven friction becomes the dominant factor over longitudinal braking risk. A skidding risk assessment method is then proposed, incorporating simulation results and braking distance thresholds. Furthermore, a comprehensive evaluation framework is established, encompassing sampling strategies, paired friction coefficient analysis for left and right wheel tracks, and risk quantification. The key contribution of this study lies in highlighting the critical yet often neglected impact of lateral friction coefficient variation on vehicle skid safety. By simulating its risk implications, this research proposes a novel overall evaluation framework for pavement skid resistance, leveraging field-collected data. The proposed approach expands the scope of traditional skid resistance assessment, offering a more holistic perspective for improving road safety.

In chemical mechanical polishing (CMP), the injection position of the polishing slurry significantly affects the interfacial hydrodynamics, abrasive transport, removal efficiency, and overall planarization. This study systematically investigates the influence mechanism of slurry injection position in the CMP process of 12-inch wafers, using a multiphase flow–discrete phase coupling CFD model combined with User-Defined Function (UDF) to constrain abrasives. The results show that the injection position directly determines the distribution of slurry between the wafer and the polishing pad. At 45 mm from the pad center, the slurry effectively fills the gap, achieving the highest material removal rate (MRR). At 105 mm, the slurry distributes most uniformly beneath the wafer, resulting in optimal planarization. However, at 165 mm, the slurry flow extends beyond the wafer center, causing abrasive agglomeration and localized over-polishing, which significantly degrades surface uniformity. Dye visualization and CMP experiments with 12-inch copper wafers validate the accuracy of the model. The findings suggest that the slurry injection position should balance removal rate and planarization to optimize the slurry distribution system, providing a theoretical basis for future optimization efforts.

Black phosphorus (BP) has been extensively utilized as a lubricant additive owing to its unique layered structure and extreme pressure anti-wear properties. By introducing black phosphorus (BP) nanosheets into Diethylenetriaminepenta (methylenephosphonic) acid (DTPMPA)/ Ethylene glycol (EG) mixture solution as additives (DTPMPA/EG-BP), the macroscopic superlubrication state on Si₃N₄/sapphire friction pair was attained at a high contact pressure of 1.83 GPa, with the coefficient of friction (COF) of 0.0067. The wear rate of DTPMPA/EG-BP (3.14×10^-9 mm³×N^-1×m^-1) exhibited a 92% reduction when compared to pure EG (3.92×10^-8 mm³×N^-1×m^-1). It was noteworthy that the BP nanosheets adsorbed on the wear surface and meanwhile the molecular layer formed by DTPMPA/EG covered the BP surface, demonstrating that the shear interface shifted from the Si₃N₄/Sapphire interface to the BP nanolayer/molecular layer interface. This interfacial transition avoided direct contact between the friction pairs and provided extremely low shear strength, resulting in ultralow COF. Therefore, the synergistic interaction between the BP nanosheets and the acid solution exerted a predominant influence in achieving superlubrication under extremely high contact pressures on the macroscopic scale. This research proposed a novel strategy to realize liquid superlubrication under high-pressure conditions and by leveraging the synergistic cooperation between 2D materials and acid molecules, it expedited the application of liquid superlubrication in industry.

Accurate monitoring of cage motion and skidding behavior is critical for ensuring the reliability of ball bearings in high-speed applications. However, existing methods are hindered by structural constraints and limitations in fluid drag modeling. This study proposes an Integral Cage-based Triboelectric Assembly (IC-TEA) for real-time, high-precision monitoring of cage skidding ratio, rotational stability, and qualitative bearing temperature rise. Experimental tests show that IC-TEA quantitatively characterizes transient cage speed fluctuations and dynamics under varying loads, rotational speeds, and oil pressures. Results reveal a non-monotonic relationship between skidding ratio and axial load: skidding peaks with no load, over-skids at intermediate loads, and minimizes under heavy loads. Thermal imaging confirms the IC-TEA output negatively correlates with lubricant temperature (26.1% decrease for 9.2 °C rise), verifying its sensitivity to both skidding and temperature. A novel instability indicator quantifies significant cage stability deterioration during over-skidding. Leveraging IC-TEA kinematics as boundary conditions, a FLUENT-based computational fluid dynamics (CFD) model predicts lubrication states and fluid drag torque. This model reveals that traditional theoretical cage speed inputs overestimate drag torque by 33.75% in skidding and underestimate it by 33.37% during over-skidding. This integrated sensor-model framework provides unprecedented accuracy in predicting lubrication effects on bearing dynamics, enabling optimized skidding mitigation strategies for high-speed applications.