Tribology Letters最新文献

This study introduces a new type of cantilever-probe system that extends atomic force microscopy to high-load, large-contact-area measurements, supporting friction studies from nano to millimeter scales. By using polymer cantilevers with colloidal microspheres, this customizable probe system (8–25 N/m cantilever stiffness; 0.08–2.5 mm probe radius) allows friction measurements on single-crystal MoS₂ under loads of 0.5–120 μN, contact areas of 0.02–10 μm², and contact pressures from 2 to 150 MPa, bridging nanoscale and microscale observations. Our findings reveal a novel scale effect, where the friction coefficient increases by a factor of 34 with a 30-fold increase in probe radius. This affordable alternative to commercial cantilevers also simplifies calibration and enhances accessibility for tribological studies in nanocomposites, MEMS/NEMS, and biological materials, offering a scalable tool for cross-scale friction research.

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This paper aims to develop core–shell nanoparticles by combining CuO (core) and reduced graphene oxide (shell) as lubricant additives and understand their action under different slide-to-roll ratios. The SRRs evaluated were 50 and 200%, with nanoparticles concentrations of 0.05 and 0.1wt%. The worn tracks were characterized through WLI, SEM, TEM and Raman Spectroscopy. The results showed that the lubrication mechanism and tribofilm formation are strongly associated with the type of contact. At SRR 200%, nanolubricant reduced friction and wear; it was observed exfoliation of nanoparticles, the CuO acted as rolling, and the rGO sheet was deposited on a worn surface. On the other hand, for SRR 50% doesn´t decrease the friction coefficient; however, a thicker tribofilm was produced with nanoparticles.

Friction and lubrication of components in mechanical transmission systems are crucial to their transmission efficiency. As for the extreme conditions, the performance of traditional liquid lubricants would be degraded, which causes significant harm to the safe and reliable operation of equipment. Therefore, the development of a high-efficiency composite lubricant is particularly important. In this study, MXene@Triethanolamine borate nanocomposite were prepared via the ultrasonic intercalation method. Furthermore, the composites were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The tribological properties of intercalated MXene@TB in the BMIMPF6 ionic liquid were evaluated under current using a ball-on-disk tribometer. The average friction coefficient of lubricant with 0.3% intercalated MXene@TB-1 was reduced by 9.8%, and its wear volume was also decreased by 36.1%. Additionally, the application of current can enhance the tribological performance of lubricant. Specifically, the wear volume of int-MXene@TB-2 was decreased by 52% due to the current-induced ion migration and lubricating film repair. Moreover, the application of current promotes the movement of nanoparticles within the ionic liquid, minimizing aggregation and further enhancing the formation of the lubrication film. The lubricant nanocomposite with high-efficiency friction reduction and anti-wear properties can be further applied in current-carrying friction field.

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Benzothiazole is widely used in biomedical applications in recent studies, in this study we coordinated it with organic molybdenum to prepare three phosphorus-free benzothiazole-organic molybdenum friction modifiers with different structures and evaluated the lubrication performance in base oil PAO6. The results showed that the three additives exhibited different friction reduction and anti-wear effects due to their different molecular structures, with benzothiazole-molybdenum oleate amide (YSMo) showing the most significant lubrication performance. At 1.00 wt%, YSMo reduced the average coefficient of friction by 30.8% and the wear volume by 95.86%. The combination of sulfur-containing nitrogen heterocyclic compounds with molybdenum source significantly enhanced the lubrication performance and effectively reduced friction and wear through physical adsorption and the formation of a dense composite chemical friction protective film (containing components such as FeS, MoO₃, and MoS₂), which further confirmed that friction-generated MoS₂ has a positive effect on the tribological performance. The lubrication performance of YSMo was superior to that of the other two additives, which depended on the polar groups and chain lengths, which provides an important theoretical basis for further optimizing the design of lubricating additives.

This study investigates the effects of graphene oxide (GO) reinforcement on the microstructural, mechanical, and tribological properties of copper (Cu) matrix composites produced via powder metallurgy and hot pressing. GO nanoparticles synthesized by the Hummers method were incorporated into Cu at different weight ratios (0.5, 0.75, and 1 wt %), and the composites were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The results revealed that GO was homogeneously distributed within the Cu matrix without forming new detectable crystalline phases, and its presence led to grain refinement and improved interfacial bonding. Hardness measurements showed that the composite containing 1 wt % GO exhibited a 109.97% increase compared to pure Cu, while tribological tests under dry sliding conditions demonstrated significant enhancements in wear resistance and reductions in the coefficient of friction. Notably, the 1 wt % GO composite achieved an 82.88% reduction in wear loss and a 51.33% decrease in friction coefficient. Post-wear SEM analysis confirmed the formation of a protective tribofilm, reduced microcrack formation, and minimized wear-induced damage. These findings highlight the effectiveness of GO as a multifunctional reinforcement for the development of high-performance Cu-based composites with superior wear resistance, making them suitable candidates for applications in electrical contact systems and other tribologically demanding environments.

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This study proposes a physics-based model for characterizing the contact behavior and state of joint surfaces. Based on the microcontact mechanics model, surface topography, material properties, loads, and asperity interactions were combined to construct a normal contact model. Subsequently, the sticking and sliding behaviors of a single asperity were characterized with the Jenkins element from the Iwan model. Conversely, a parallel arrangement of multiple Jenkins elements represented the overall stick–slip behavior. A distribution function incorporating non-Gaussian distribution and asperity interactions was derived to describe the tangential yield force distribution, thereby constructing a physically explicit tangential contact model. Finally, the results of the predictive model were validated against the experimental data. A slip ratio was introduced to quantifiably evaluate the surface contact states—full stick, stick–slip, and gross slip micromotion, and the factors influencing the contact characteristics of the joint surface were investigated.

Understanding the relationship between sliding velocity, temperature, friction, and wear is of fundamental importance in materials science and engineering. Here, we explore sliding friction and wear of a silicon carbide nano-asperity sliding over a silicon carbide substrate for a broad range of temperatures and velocities using molecular dynamics simulations. Our study reveals three distinct friction regimes over four velocity decades: velocity-weakening at moderate velocities, velocity-strengthening at high velocities, and an additional velocity-strengthening behavior at very low velocities and elevated temperatures. We theoretically describe these findings with physics-based friction models. For the low-velocity regime, we refine the Prandtl-Tomlinson model by incorporating a logarithmic aging mechanism that accounts for surface diffusion-driven contact evolution. For the high-velocity regime, we introduce a linear viscous friction model with an Arrhenius temperature dependence. These models demonstrate strong agreement with the molecular dynamics simulation results in their respective velocity regimes. We then explore wear mechanisms, distinguishing between atomic attrition at low velocities and collective material removal at high velocities, thus providing a comprehensive framework for understanding the velocity and temperature dependence of nanoscale friction and wear of silicon carbide.

The progressive escalation of operational velocities in high-speed railways has intensified cyclic contact stresses at wheel–rail interfaces, leading to accelerated fatigue failure. Hence, it is essential to create new wheel–rail materials with superior performance to align with the requirements of high-speed railway systems. This paper introduces a newly developed high-speed wheel steel (CLD400) that demonstrates enhanced rolling contact fatigue (RCF) performance and the influence of running speed on RCF damage in wheel steel. The results reveal that the CLD400 wheel steel exhibits excellent RCF life, which is 5.9 times higher than that of ER8 wheel steel. The performance of wheel steel can be effectively enhanced by decreasing the size of the austenite grain, pearlite colony, and interlamellar spacing, while increasing the pearlite content. In situ observations indicate that under oil-lubricated conditions, cracks gradually develop on the contact surface of the wheel steel and eventually expand into noticeable peeling pits, leading to material failure. As the cycles increases, the area and perimeter of defects on the wheel steel contact surface gradually increase, whereas the shape factor gradually decreases. As running speed increases, the deterioration of the wheel's steel material begins sooner, although with a reduced level of severity. The force driving crack growth decreases with speed increases, resulting in smaller RCF crack sizes. These findings enable the targeted design of wheel materials for 400 km/h high-speed trains.

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Neutron reflectometry is a technique for measuring structure near planar interfaces that has been previously used to non-destructively characterize the polymer density of hydrated, dilute, and soft materials. Previous investigations have conducted neutron reflectometry measurements of liquids, gels, emulsion, and polymer solutions at rest, in compression, and subject to shear stress. However, correlating structure with tribological properties of soft materials presents significant experimental challenges for prior instruments due to wall slip, sample thickness, and structural heterogeneity (e.g., depth-wise gradients). A linear reciprocating tribometer offers several advantages for in situ neutron reflectometry studies, including uniform velocity profiles, constant shear stress over large regions of interest, and independent control of normal force and sliding velocity during measurements. This work outlines basic considerations for the design of a custom linear reciprocating tribometer that operates in a neutron beamline and includes commissioning measurements. The tribometer is designed to compress soft and hydrated materials against linearly reciprocating silicon disks. The three key design considerations for this tribometer are (1) safety, (2) neutron transmission, and (3) sample positioning. This instrument design will enable in situ studies of soft matter and illuminate the role of interfacial structure on tribological phenomena.

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