Tribology Letters最新文献

Accurate, traceable force calibration remains a challenge for microtribometers because of lateral/normal cross-talk and operating-point dependence bias in conventional procedures. We present a traceable force calibration (TFC) that solves the full 2 × 2 calibration matrix (C₁-C₄) from angle-resolved loading using a diamagnetic-levitation spring with a microbalance as an SI-traceable force standard. A known load is applied while the cantilever is tilted through multiple angles; linear slopes ΔV_x,z/ΔF₁ at each angle provide sufficient equations to recover C without neglecting cross-talk. Using 18 angles, TFC yields stable coefficients C₁ =  − 746.98 ± 0.01 μN/V and C₄ =  − 737.17 ± 0.45 μN/V, with small cross-terms C₂ = 3.372 ± 0.003 μN/V and C₃ =  − 45.14 ± 0.63 μN/V. Subsampling shows convergence with only 3–4 angles, and a ± 1° reference-angle bias changes C₁ and C₄ by ≤ 1.01% and ≤ 0.49%, respectively. Compared head-to-head with the diamagnetic-levitation force-calibration (DLFC) route, TFC produces C₁ values invariant to angle choice, whereas DLFC yields set-point (V_z)-dependent results and larger scatter (e.g., C₁ =  − 758 ± 41 μN/V). TFC thus offers a compact, low-uncertainty, SI-traceable workflow that quantifies cross-talk and delivers reliable calibration over micro- to milli-newton forces, enabling high-precision, reproducible microtribometry.

Leveraging advantageous properties including low density, high specific strength, and corrosion resistance, titanium alloys have become essential structural joining components in aerospace systems. Nevertheless, their inherently low hardness and poor wear resistance constrain reliability and service life in demanding in-service conditions. This study aims to enhance their surface properties through a combination of ultrasonic shot peening (USP) and thermal oxidation (TO). The results indicate that USP pretreatment refines surface grains, increases surface roughness, and optimizes oxygen atoms diffusion pathways, resulting in the formation of a thicker oxygen diffusion layer. Following the USP/TO composite treatment, a composite strengthening layer is formed on the Ti-6Al-4V alloy, consisting of Rutile TiO₂, Brookite-TiO₂, and other phases, which enhances both the microhardness of the surface and subsurface. Notably, the sample treated with USP/TO for 5 min exhibits a 98% reduction in wear volume and mitigates abrasive wear.

Graphical Abstract

A simple and nonsynthetic way of bicomponent supramolecular gel lubricants was prepared by adding carboxylic acid and sodium organosulfur oxy-salts with varying chain lengths and saturation degrees into white oil (WO). The gelling properties have shown that the bicomponent supramolecular gelator with longer alkyl chains and higher saturation, such as stearic acid and sodium dodecyl sulfate (SA-SDS), possessed better gelling properties. SA self-assembles to helical fibers, and SDS enhances fiber cross-linking via the noncovalent interaction with SA, leading to the formation of three-dimensional networks with significantly increased rigidity. Tribological data show that SA-SDS gel reduces wear scar diameter and friction coefficient by approximately 25 and 24% compared to WO. And the gel system of SA-SDS in WO has better anti-friction and anti-wear performances than the sol system. This is because the multilayer tribofilm consisting of oxide layers, carbonaceous species, and organic films is formed at the interface, significantly improving lubrication. These findings provide insights into the design of supramolecular gel-based lubricants for enhanced friction and wear control.

Evaluation of boundary lubricants is crucial for enhancing the energy efficiency of a system, as the boundary lubrication (BL) regime involves direct asperity contact and exhibits the highest friction. Fatty acids are widely used as friction modifiers in BL regimes, forming tribofilms that reduce direct asperity contact and lower friction. This study examines the effect of molecular unsaturation on the frictional behaviour of oleic acids across temperatures. A Force-Controlled Pendulum Tribometer (FCPeT), which operates on energy dissipation methodology, was used to evaluate the frictional performance of a blend of oleic acid with base oil at temperatures of 27 °C, 60 °C, and 100 °C. The FCPeT quantifies friction by measuring energy dissipation during sliding. Results indicate that the coefficient of friction increases with temperature, rising from 0.10 at 27 °C to ~ 0.12 (steady state) at 100 °C. FTIR and XPS analyses of the wear track confirmed tribofilm formation. The XPS results reveal that at higher temperatures, tribofilm degrades, contributing to increased frictional dissipation.

Graphical Abstract

The tribo-dynamic behaviors of third-body colloidal particles (CPs) at the soft–hard contact interface significantly impact the substrate surface performance. To explore the differences of the stick-slide and roll-slide tribo-dynamic behaviors of CPs, the tribological behaviors of fixed and free CPs on hydrophilic silicon substrates were investigated using the colloid probe and nano-manipulation technology in atomic force microscopy, respectively. In contrast to the velocity-enhanced static friction commonly observed in fixed CPs, the static friction of free CPs exhibits a logarithmic decrease with increasing velocity. This phenomenon can be attributed to the transition from a “sliding-dominated” to a “rolling-dominated” driving state of the CPs as velocity increases. The findings enhance the understanding of tribo-dynamic behaviors of CPs at the nanoscale and provide a foundation for the deliberate design and optimization of CP-based applications in chemical mechanical polishing (CMP) and post-CMP cleaning technologies.

In this paper, MoS₂–ZrN composite coatings with a Chromium interlayer were fabricated using magnetron sputtering technique. The structure and properties of the MoS₂–ZrN composite coatings with different ZrN contents were systematically investigated. It was observed that both hardness and elastic modulus improved with increasing ZrN content, reaching peak values of 6.60 GPa and 109.95 GPa, respectively, at 30% ZrN. Tribological performance was assessed using steel balls with varying surface roughness, where the lowest coefficient of friction of 0.09 was recorded when the coating was paired with a smoother counterface. Abrasive wear was identified as the dominant wear mechanism. Additionally, a contact mechanics model was developed to describe the interaction between a rough spherical indenter and the coating surface. This model enabled analysis of how surface roughness and coating mechanical properties jointly affect macroscopic contact parameters, such as real and nominal pressure distributions and contact radius. A good qualitative agreement was found between the experimental results and theoretical predictions, confirming the model's validity.

Graphical Abstract

This study examined the impact of sliding speed on the wear process of brass by integrating thermodynamic principles with molecular dynamics simulation. The simulation findings indicate that as the sliding speed increases, the strain rate of the workpiece rises while the tensile stress decreases and the compressive stress increases. Consequently, the tangential force remains constant regardless of sliding speed, whereas the normal force increases with higher speeds. Additionally, the temperature of the workpiece rises with increasing sliding speed, leading to a more significant thermal softening effect. Due to the interplay between strain rate hardening and thermal softening, the wear of the workpiece initially decreases and then increases as the sliding speed continues to rise. The specific wear rate, specific wear amount, and degradation coefficient all decrease with increasing sliding speed, suggesting that cutting becomes more challenging at higher speeds. Therefore, careful consideration is necessary when selecting the cutting speed to achieve efficient machining. This study serves as a valuable reference for the machining of metal materials.

Three different reinforcing fillers were selected for winter tire tread rubber. After improving the testing method using the LAT100 testing machine, tests were conducted on the effect of rubber surface roughness on ice grip and wet grip performance, as well as research on the effect of load and speed on the rubber-ice friction coefficient at different temperatures. The results showed that with the increase of the macroscopic roughness of the rubber surface, the frictional force between the rubber and the ice surface decreased, the frictional force between the rubber and the wet road surface increased; With the increase of load and speed, the friction coefficient of rubber on the ice surface decreases, and the change is more obvious on the – 15 ℃ ice surface compared to the – 5 ℃ ice surface, and the friction coefficient on the – 15 ℃ dry ice surface is greater than that on the – 5 ℃ wet ice surface; In order to better predict the results of the real vehicle test, in the LAT ice friction test, the load was selected from 75 to 100N, the speed was selected from 0.6 km/h, and the run-in conditions specifically for winter tread rubber were determined. This provided theoretical support for improving the accuracy of indoor predictions of real vehicle ice grip test results and enriched the research on the rubber-ice friction mechanism.

Using a custom-built microtribometer, the stick–slip behavior of a single elastic string in Hertz contact with a cylindrical glass lens was observed in situ, collecting dynamic contact area and friction force data during the adhesion phase. The results indicate that stick–slip occurs periodically due to repeated contact and elastic deformation. The friction pair was modeled for both translational and rotational movement, quantifying energy changes during the adhesion phase. It was inferred that slip occurs due to instability when the contact area reaches its maximum, which is possibly determined by a combination of factors including surface roughness, rubber deformation, and cylindrical rotation. These findings provide new insight into the macroscopic frictional properties of fiber-structured surfaces.

It was shown in a previous paper that friction in highly loaded non-conforming contacts correlated with the formation of a glassy state of the lubricant, for the only lubricant studied (benzyl benzoate). The aim of the present paper is to extend this conclusion to other types of fluid: a model fluid from the literature (glycerol) and a well-known lubricant (squalane). The characterization of these fluids in the bulk by Brillouin spectroscopy shows a similar evolution of their behavior with pressure and makes it possible to identify their glass transition pressure. Furthermore, comparison of this characterization with friction data for squalane validates the correlation previously established for benzyl benzoate. In a second part, the structural relaxation time of benzyl benzoate is derived from Brillouin spectra to probe the influence of hydrostatic pressure on fluid dynamics. This parameter, superimposed on the previous friction measurements, shows that the dynamics of the molecules is highly reduced at high pressures, which explains the macroscopically solid-like behavior of the lubricant. This result suggests that the relaxation time is an essential parameter for the correct modeling of highly loaded lubricated contacts.