Search Results (383)

CrN/DLC composited coatings were deposited on 431 stainless steel, and their structure was analyzed, with particular emphasis on the influence of CrN content on the coating properties. X-ray photoelectron spectroscopy (XPS), nanoindentation testing, scratch testing, and reciprocating tribometry were employed to characterize the chemical composition, mechanical properties, adhesion strength, and tribological performance of the coatings, respectively. Structural analysis indicates that when the ratio of CrN/Cr₂N is relatively low (<1), a high content of chromium dinitride (Cr₂N) is formed in the interlayers, resulting in a porous and loose coating structure. When the ratio achieves 1:1, an optimal balance, with the CrN content reaching a maximum of 21.04% and the Cr₂N content decreasing to a minimum of 20.68%, the densification degree of the coatings is increased, the coating adhesion strength is improved to 11.87 N. Meanwhile, the enhanced formation of the CrN phase improves the hardness to 12.27 GPa. Tribological test results demonstrate that when the ratio is approximately 1:1, the coating exhibits the lowest friction coefficients under dry sliding, deionized water, and artificial seawater conditions (0.0932, 0.1409, and 0.1021, respectively), as well as the minimum wear rates. With the decrease in CrN content of the coatings, the interfacial mismatch degree of the coatings is aggravated, which leads to not only more interfacial defects but also a relatively loose structure, as well as a decrease in the bonding strength (6.81 N), hardness (5.22 GPa), and deformation resistance. Therefore, an excessive Cr₂N phase may degrade the hardness-to-elastic modulus ratio (H/E) of the coatings by increasing interfacial mismatch and reducing structural compactness. Full article

Aiming to address the problems of shield chamber blockage and poor muck discharge faced by earth pressure balance shields during tunneling in sandy strata, bentonite slurry is used for muck improvement. Using a multi-scale approach combining macro-scale experiments, micro-scale analysis, and molecular dynamics simulations, this study systematically investigates the interface interactions between particles of sandy soil in shield tunneling and the improvement mechanism of sodium-based bentonite slurry additives. Through the macroscopic experiment, the sodium bentonite slurry soil–water ratio of 1:7 and injection ratio of 25% showed the best improvement effect. After improvement, the permeability coefficient decreased by 99.72%; the cohesion of the excavated soil increased from 3.055 kPa to 11.458 kPa, representing a 275.06% increase; and the angle of internal friction decreased from 42.318° to 36.985°, a decrease of 12.60%. The improvement was significant. Through SEM, XRD, and FTIR microanalysis, it is found that bentonite slurry forms a flexible film on the surface of sandy soil. By coating sand particles, filling voids in the soil, and enhancing interparticle cohesion, it improves the properties of the soil. On the nanoscale, a Na-MMT/SiO₂ system model is established based on molecular dynamics simulations to elucidate the interactions between bentonite slurry and sand particle interfaces. The results indicate the presence of van der Waals forces and hydrogen bonds between Na-MMT and SiO₂. Interlayer water molecules form a hydrogen bond network that strengthens interfacial bonding, enabling bentonite slurry to tightly adhere to soil particle surfaces. This improves the microstructure of the soil, thereby enhancing its macroscopic properties. Full article

In this study, carboxyl groups were introduced onto CNT surfaces via acid oxidation, and Ag nanoparticles were successfully deposited onto the CNTs through an in situ chemical reduction method. At an Ag-to-CNTs100 mass ratio of 3:1, the as-prepared composite achieved a thermal conductivity of 1.45 W/(m·K) in dimethyl silicone oil, representing enhancements of 187.5% and 76.9% relative to pure Ag nanoparticles and pristine CNTs100, respectively, at equivalent loadings. Concurrently, tribological tests revealed that the AgHTs-3 at a 3:1 mass ratio and 25 wt% loading exhibited a steady-state friction coefficient of 0.08–0.12, reflecting an approximately 72% reduction compared with pure dimethyl silicone oil. Electrical conductivity measurements demonstrated that CO-CNTs100 attained saturation at 30 wt% with a resistivity of 36.5 Ω·m, whereas the AgHTs-3 nanocomposite achieved a resistivity of 4.7 Ω·m at 35 wt%. The incorporation of Ag nanoparticles effectively enhanced the overall performance of the nanocomposites. Through the formation of a synergistic heterostructure with carboxyl-functionalized carbon nanotubes, the composite not only significantly improved the thermal conductivity of dimethyl silicone oil but also effectively optimized the interfacial lubricating film while substantially reducing the friction coefficient and wear volume. Moreover, the introduction of silver promoted the dispersion stability of the composites in dimethyl silicone oil, enabling higher filler loadings and thereby effectively boosting electrical conductivity. Full article

Drag-reducing coating technology is a core approach to enhancing the performance of ice and snow sports equipment. By regulating the interfacial characteristics between the equipment surface and the ice or snow medium, it significantly reduces frictional resistance during motion, thereby optimizing athletes’ speed performance and control precision. This paper aims to review the current research status and challenges in this technological field. The review first elaborates on the fundamental principles of applying drag-reducing coatings to key equipment such as skis, sleds, and ice skates, covering current mainstream coating material systems, key preparation processes, and comprehensive performance evaluation methods. Furthermore, integrating multidisciplinary advances in surface engineering, fluid dynamics, and materials science, this review specifically examines how these disciplines can be harnessed to address the unique tribological challenges of snow/ice interfaces. It focuses on cutting-edge research directions such as micro-nano-structured coatings driven by biomimetic design concepts and smart coatings with environmental responsiveness. By synthesizing existing research achievements and potential technological bottlenecks, this paper aims to provide a systematic, theoretical basis and innovative ideas for the future development of a new generation of high-performance, intelligent ice and snow sports equipment. Full article

HfC, TaC, and HfTaC composite coatings were successfully fabricated on SiC-coated carbon/carbon (C/C) composites using the double glow plasma alloying (DGPA) technique. The microstructure, mechanical properties, and tribological behaviors of the coatings were systematically investigated. The HfTaC coating exhibited a dense and uniform structure with good interfacial integrity and a compositionally graded transition layer, effectively relieving thermal stress. The hardness of HfTaC and HfC coatings (approximately 12 GPa) was higher than that of the TaC coating. Moreover, the higher K value (1.02) and H/E ratio (H/E = 0.09, H³/E² = 0.085 GPa) indicate that the HfTaC coating exhibits good load-bearing capacity and toughness. Under both 5 N and 15 N loads in the reciprocating friction, the HfTaC coating maintained the lowest and most stable friction coefficient (~0.18). Under the 15 N load, it exhibited the smallest specific wear rate. Observation of the wear scars revealed that the HfC and TaC coatings suffered from pore formation and flake-like spallation, while the HfTaC coating retained structural integrity with only minor cracks. In high-temperature ball-on-disc friction tests up to 500 °C, the wear mechanism of the HfTaC coating gradually transitioned from mild abrasive wear to severe oxidative and adhesive wear, yet the HfTaC coating still provided effective protection. These findings demonstrate that the DGPA-fabricated HfTaC coating is a promising candidate for enhancing the wear resistance and service durability of C/C composites. Full article

High-load sliding components, including gun barrels, are susceptible to accelerated wear and damage due to coupled thermal-mechanical stresses and reciprocating frictional conditions. Therefore, enhancing their operational lifespan requires the application of wear-resistant coatings with high melting points for effective surface protection. In this study, Ta-10W alloy coatings were deposited on CrNi3MoVA steel substrates through electricspark deposition, focusing on deposition voltage as a critical parameter. Experimental results indicate that the Ta-10W coatings are primarily composed of α-Fe, α-Ta₂O₅, δ-Ta₂O₅, α-Ta(W), and Fe-W intermetallic phases. An increase in deposition voltage facilitates enhanced melting and mass transfer, thereby promoting solid solution and oxidation strengthening, which results in improved hardness. However, higher voltages also induce defects such as porosity and microcracks. Hardness measurements and friction-wear tests demonstrate that coatings deposited at 80 V exhibit optimal performance, attaining the highest hardness (~753 HV) and a friction coefficient similar to that at 60 V. Conversely, the friction coefficient increases at 100 V due to defects and coating spalling. The wear mechanism transitions from adhesive wear at 60 V to adhesive wear with minor plastic deformation at 80 V and ultimately to spalling wear at 100 V. Finite element thermomechanical simulations reveal that increasing voltage significantly elevates the equivalent interfacial stress (600–1150 MPa), thus correlating with the propensity for microcracks to propagate into longitudinal semi-penetrating cracks at elevated voltages. This study establishes a theoretical foundation for optimizing electricspark deposition process parameters and contributes to the reliability design of Ta-W alloy coatings. Full article

Driven by global environmental regulations that strictly limit copper content in brake pads, traditional copper-based friction materials face significant challenges due to their negative ecological impacts. Consequently, the development of sustainable, copper-free alternatives has become an inevitable trend in the braking industry. This study proposes a novel approach to developing high-performance green friction materials by utilizing a synergistic combination of agricultural wastes, specifically corn cobs, wheat straw, rice husks, and sugarcane bagasse, and carbon fibers. Research indicates that the friction coefficient of the synergistic formulation remains stable within the range of 0.35 to 0.48. Compared with the control group, this formulation achieves an average reduction in the wear rate of 19.28% and an increase in the recovery rate of 5.15%, demonstrating superior tribological performance. The synergistic interfacial regulation between carbon fibers and agricultural waste facilitates the construction of a smooth and stable friction layer, which maintains consistent performance during extended operating conditions. Among all formulations investigated, the composite reinforced by the synergy of corncob and carbon fiber exhibits the most prominent comprehensive properties, with the wear rate decreasing by 28.73% and the recovery performance improving by 4.05% relative to the specimen containing copper fibers. This work not only provides a new pathway for the sustainable development of green friction materials but also offers a theoretical basis for the high-value utilization of agricultural waste resources. Full article

The friction-induced stick-slip vibration (FISSV) generated by intense friction between the brake disc and brake pads of high-speed trains is a critical issue affecting braking stability, the service life of foundational braking components, and ride comfort. The floating friction block structure, which effectively regulates interfacial contact characteristics through the elastic deformation of disc springs, thereby improving tribological behavior, represents an effective approach for mitigating FISSV. However, the topic of how to design the floating structure of the friction block to produce the best suppression impact on FISSV emerges, using the choice of disc spring material as an example. Thus, the purpose of this study is to look at how disc spring material affects stick-slip vibration (SSV) at the high-speed train floating brake interface. Four typical disc spring materials—304 stainless steel, Mubea-specific spring steel, 50CrVA high-alloy spring steel, and 60Si₂MnA silicon-manganese spring steel—were selected. Through braking tribological tests and explicit dynamics-wear coupling simulations, the effects of material differences on interfacial friction-wear characteristics and SSV behavior were systematically studied. The findings show that the stiffness of the disc spring material greatly influences the dynamic responsiveness of the system and the contact pressure distribution at the braking interface, elasticity, and damping characteristics. 60Si₂MnA spring steel, owing to its excellent elastic recovery and load equalization capability, promoted the formation of uniformly dispersed medium-to-small contact platforms on the interface, resulting in the mildest wear. Concurrently, its system vibration energy exhibited a more dispersed distribution in the frequency domain, with low SSV intensity and weak nonlinear behavior, demonstrating the best comprehensive performance. Materials with poorer compatibility, such as 304 stainless steel, tended to cause localized stress concentration, exacerbating wear and intensifying severe high-frequency SSV. The influence mechanism of disc spring material at the interface is shown by this work, providing an important basis for material optimization and vibration suppression design in floating brake pad structures. Full article

Boundary lubrication plays a crucial role in determining the service performance and operational lifespan of mechanical components. However, continuum mechanics models and experimental studies are unable to elucidate the dynamic evolution of intermolecular interactions at the interface under boundary lubrication from a microscopic perspective, including phenomena such as asperity contact and lubricant film rupture. In this study, a molecular dynamics simulation approach was employed to construct a boundary lubrication friction model incorporating lubricant molecules, aiming to investigate the influence of applied load and asperity height on the dynamic evolution of atomic interactions at the interface from the perspective of energy variation, under conditions both with and without asperity contact. The results indicate that van der Waals interactions dominate the frictional response, and severe asperity contact leads to a sharp increase in van der Waals energy, which in turn results in a decrease in normal force, thereby increasing the friction coefficient. When the upper and lower surfaces remain separated by the lubricant, an increase in van der Waals energy leads to higher friction force, consequently elevating the friction coefficient. In the absence of contact, the friction coefficient decreases with increasing load; however, once asperity contact occurs, higher loads accelerate lubricant film failure and intensify direct interfacial contact, leading to more pronounced stick–slip oscillations and increased wear. This study provides atomic-scale insights for the design and performance optimization of boundary lubrication interfaces. Full article

Accurate characterization of the true tire–pavement contact state is essential for understanding pavement friction; yet conventional texture indicators and nominal contact assumptions cannot directly represent the actual interfacial interaction between rubber and pavement. This study proposes a rapid and non-destructive method for measuring three-dimensional tire–pavement true contact texture under different loads. A materials testing system was used to apply controlled loads to a rubber pad–carbon paper–pavement assembly, and the resulting imprints were combined with three-dimensional laser profilometer data and support-curve-based slicing to determine the real contact area ratio, penetration texture depth, and self-affine fractal dimension. Tests on nine asphalt pavement samples under loads from 5 to 20 kN showed that the real contact area ratio increased with load but remained below 40% at 20 kN. The predicted contact area from the reconstructed 3D texture agreed well with the imprint-based results, with an absolute error not exceeding 2.59%. Penetration texture depth showed a stronger relationship with skid resistance than fractal dimension. The proposed method provides a practical means of capturing effective tire–pavement contact parameters and offers useful inputs for laboratory-based skid resistance evaluation and texture-informed friction modeling. Full article

To improve coating adhesion and tribological stability on aircraft-grade aluminum, this work utilizes periodic fiber-laser microtexts as a surface-engineering pre-treatment before applying an epoxy primer. AA2024-T3 panels were imprinted with rhombus, hexagon, and circular lattices (scale factors 100–250 µm; scan speeds 250–750 mm s⁻¹), then primed with an aerospace epoxy primer and evaluated within reciprocating sliding wear tests. Areal profilometry and sessile-drop goniometry measured topography and wettability, whereas friction–distance traces and scratch-track metrology resolved interfacial integrity. The textures expanded surface area and modified energy states in a geometry- and scale-dependent fashion, producing stable friction plateaus and smaller, less-lateral scratch scars compared to the untextured reference. Circular dimples reliably provided the best damage-tolerant behavior, a function of improved mechanical interlocking and debris/film management (reservoir and micro-trap effects), whereas polygonal lattices evidenced greater sensitivity to both scale and speed. Factorial analyses disclosed prevalent interaction effects amongst geometry, scale, and scan speed, reinforcing the notion that performance arises from co-optimized texture architecture rather than a single parameter. In systemic terms, laser-defined microtexts complemented with aerospace-standard primers represent a controllable pathway to vary friction, dampen wear, and improve coating–substrate adhesion. These results provide practical selection guides; and a broad selection prefers larger, well-spaced circular dimples for best-in-class performance and a transferable framework for designing texture-coating systems across aerospace and allied manufacturing contexts. Full article

Under complex friction conditions, base oils usually exhibit insufficient friction-reducing and anti-wear performance, poor shear resistance of the lubricating film, and weak interfacial adsorption stability. Herein, graphene oxide (GO) was surface-modified with the silane coupling agent KH550 and compounded with Ag nanoparticles to fabricate a silver/modified graphene oxide (Ag/KGO) composite lubricant additive. The microstructure and chemical characteristics of the Ag/KGO composite were characterized by SEM, XRD, FTIR, and Raman spectroscopy. Tribological tests performed on a Si₃N₄/GCr15 friction pair demonstrated that the lubricant containing 0.15 wt% Ag/KGO achieved the optimal tribological performance, with the average friction coefficient decreasing to 0.053, 51.8% lower than that of the base oil, and the wear scar width and depth decreasing by 34.5% and 75.7%, respectively. Molecular dynamics simulations revealed that Ag/KGO enhanced the interfacial adsorption strength and improved the shear stability of the lubricating film. Mechanism analysis indicated that KGO facilitated the formation of a stable lubricating film at the friction interface, while Ag nanoparticles acted as nano-bearings. Their synergistic effect reduced interfacial shear resistance and alleviated wear. These findings provide theoretical support for the design and development of high-performance composite lubricant additives. Full article

To elucidate the role of environmentally friendly oxide additives in a molybdenum disulfide (MoS₂)-based solid lubricant, this study investigates the tribological behavior of a MoS₂–TiO₂ coating deposited via a spray-bonding process and compares it with a commercial Sb₂O₃-containing formulation (Everlube 620C). Interfacial characteristics and wear-related mechanisms were systematically analyzed using scanning electron microscopy (SEM), focused ion beam (FIB), Raman spectroscopy, and X-ray diffraction (XRD). The MoS₂–TiO₂ coating exhibited a higher steady-state coefficient of friction (0.35–0.45) and wear compared to the baseline. Its wear behavior was governed by fracture-induced three-body abrasion, driven by the hard and brittle nature of TiO₂, which promotes stress concentration at particle–matrix interfaces, crack initiation, particle pull-out, and debris generation. These processes suppress the formation of a desirable MoS₂-rich tribo/transfer film, leading to deformation-dominated friction. Overall, the findings indicate that the intrinsic mechanical properties and interfacial behavior of TiO₂ limit its effectiveness as an additive in MoS₂-based coatings, highlighting the importance of additive selection and compatibility in achieving optimal tribological performance. Notably, this study was performed at an additive volume fraction equivalent to that of Sb₂O₃ in Everlube 620C, serving as a foundation and indicating that further optimization of TiO₂ particle size and concentration is required to achieve comparable performance. Full article

Diamond-like carbon (DLC) coatings are widely used as protective and self-lubricating surfaces in metal–metal contacts. Their frictional behavior is governed by the formation and evolution of carbon-rich transfer layers (TLs), which can be tailored through functionalization with carbon nanomaterials. Recent studies have shown that graphene sheets (GSs) and nanodiamonds (NDs) act synergistically to achieve ultra-low friction in microrough (~0.2 μm) metal–DLC contacts under dry N₂ at a 1 N load. Here, we probe how this lubrication mechanism evolves with increasing load from 1 to 10 N—corresponding to local contact pressures up to ~11–16 GPa—respectively, in dry N₂ and humid air conditions. Ball-on-disk experiments are performed on an industrial hydrogenated DLC coating sliding against stainless-steel. In dry N₂, GS–ND functionalization yields a low and stable coefficient of friction across the entire load range, reaching a minimum of about 0.05. In humid air, higher friction levels are observed across all loads (CoF ~0.10–0.15), accompanied by oxidation-driven modifications of both wear debris and the counterface contact region, with oxygen content increasing by more than a factor of three compared to dry N₂. Detailed microscopy and spectroscopy analyses indicate that enhanced lubricity in dry N₂ arises from TLs incorporating GSs, NDs, and nanoscroll-like structures, whereas humid air promotes interfacial amorphization and oxidation, leading to load-insensitive friction and boundary lubrication effects through physisorbed water molecules. Full article

Long-distance pulling of submarine cables inside horizontal directional drilling (HDD) steel casings is often limited by high interfacial resistance, rapid pulling-force accumulation, and poor adaptability to muddy-sandy environments. In addition, conventional outward-extending roller devices are relatively bulky, which increases the required casing diameter and reaming size. To address these issues, this study proposes a compact ball-frame and tensioned steel cable series drag-reduction device. An 18 m local full-scale pulling test system was established using an actual engineering submarine cable, a practical-scale steel casing, and full-scale drag-reduction devices. The effects of pipe curvature, device spacing, terminal reaction force, and in-casing medium conditions on the equivalent friction coefficient were investigated. The results show that the equivalent friction coefficient of the submarine cable–steel casing system is maintained at 0.25–0.36 under most test conditions, which is significantly lower than the commonly adopted value of 0.55 for direct contact. Based on the experimentally identified parameters, a simplified assessment model for ultimate pulling length was established for construction scheme comparison and preliminary capacity estimation. The results indicate that, with the implementation of the tensioned steel cable series system, the ultimate pulling length increases from 431/696 m for direct pulling to 954/1424 m. These results provide valuable technical references for drag-reduction scheme selection and preliminary construction-capacity assessment in HDD landfall sections. Full article