Search Results (82)

Hydrogenated amorphous carbon (a-C:H) films are widely valued for their excellent mechanical strength and low friction, but their performance significantly degrades at elevated temperatures, limiting practical applications in aerospace environments. In this work, we aimed to enhance the high-temperature tribological behavior of a-C:H films through controlled silicon (Si) doping. A series of a-C:H:Si films with varying Si contents were fabricated via direct current magnetron sputtering, and their microstructure, mechanical properties, and friction behavior were systematically evaluated from room temperature up to 400 °C. Results show that moderate Si doping (8.3 at.%) substantially enhances hardness and wear resistance, while enabling ultralow friction (as low as 0.0034) at 400 °C. This superior performance is attributed to the synergistic effects of transfer layer formation, preferential Si oxidation, and tribo-induced graphitization. This study provides new insights into the high-temperature lubrication mechanisms of Si-doped a-C:H films and demonstrates the critical role of Si content optimization, highlighting a viable strategy for extending the thermal stability and lifespan of solid-lubricating films. Full article

This study develops novel superhydrophobic UHMWPE/PTFE/PVA composites via hot-pressing sintering to achieve ultra-low friction and enhanced wear resistance. The ternary system synergistically combines UHMWPE’s mechanical stability, PTFE’s lubricity, and PVA’s dispersion/binding capability. Results show PTFE disrupts UHMWPE crystallization, reducing melting temperature by 2.77 °C and enabling energy dissipation. All composites exhibit hydrophobicity, with optimal formulations (UPP3/UPP4) reaching superhydrophobicity. Tribological testing under varied loads and frequencies reveals low friction, where UPP1 achieves a COF of 0.043 and wear rate below 1.5 × 10⁻⁵ mm³/(N·m) under low-load conditions. UHMWPE oxidative degradation forming carboxylic acids at the interface (C=O at 289 eV, C–O at 286 eV). Formation of tungsten oxides (WO₃/WO₂), carbides (WC), and transfer films on steel counterparts. A four-step tribochemical reaction pathway is established. PVA promotes uniform transfer films, while PTFE lamellar peeling and UHMWPE chain stability enable sustained lubrication. Carbon-rich stratified accumulations under high-load/speed increase COF via abrasive effects. The composites demonstrate exceptional biocompatibility and provide a scalable solution for biomedical and industrial tribological applications. Full article

Diamond-like carbon (DLC) coatings have emerged as a focal point in advanced carbon materials research due to exceptional tribological properties, including ultralow friction coefficient, exceptional wear resistance, ultrahigh hardness, and chemical inertness. Deposition of DLC coatings on metal components represents an innovative solution to enhance wear resistance in engineering applications. However, suboptimal adhesion strength between coatings and substrates, coupled with inherent material limitations, critically compromises the tribological performance. This review systematically examines recent advances in improving the wear resistance of DLC-coated metal components. First, the fundamental wear mechanisms governing both metallic substrates and DLC coatings under service conditions are elucidated. Next, three pivotal technologies, substrate material treatment/strengthening, coating structure design, and elemental doping, all demonstrating significant efficacy in wear resistance enhancement, are critically analyzed. Furthermore, a comparative assessment of these techniques reveals the synergistic potential in hybrid approaches. Finally, a concise summary of the outlook is presented. Full article

This work studies the fabrication of CoCrFeNiMo high-entropy alloy (HEA) coatings via coaxial powder-fed laser cladding, addressing porosity and impurity issues in conventional methods. The HEA coatings exhibited eutectic/hypereutectic microstructures under all laser power conditions. A systematic investigation of laser power effects (1750–2500 W) reveals that 2250 W optimizes microstructure and performance, yielding a dual-phase structure with FCC matrix and dispersed σ phases (Fe-Cr/Mo-rich). The coating achieves exceptional hardness (738.3 HV_0.2, 3.8× substrate), ultralow wear rate (4.55 × 10⁻⁵ mm³/N·m), and minimized corrosion current (2.31 × 10⁻⁴ A/cm²) in 3.5 wt.% NaCl. The friction mechanism of the CoCrFeNiMo HEA coating is that in high-speed friction and wear, the oxide film is formed on the surface of the coating, and then the rupture of the oxide film leads to adhesive wear and abrasive wear. The corrosion mechanism is the galvanic corrosion caused by the potential difference between the FCC phase and the σ phase. Full article

Silicon-doped tetrahedral amorphous carbon (ta-C:Si) coatings are promising materials for achieving ultralow friction in water-lubricated environments, attributed to the formation of Si(OH)_x-based tribofilms. However, the deposition process via filtered cathodic vacuum arc (FCVA) often introduces large particles into the film, increasing surface roughness and causing accelerated wear during the initial sliding phase, despite the high hardness of the coating. In this study, ball-on-disk tribological tests were performed to investigate the wear behavior of ta-C:Si coatings under water lubrication. Friction coefficients, wear volume, and surface roughness were analyzed over various sliding durations. The Archard wear equation and the plasticity index were used to analyze wear and contact behavior. The friction coefficient decreased from 0.14 to 0.04 within the initial 100 m section, and the surface roughness of ta-C:Si decreased sharply from 0.35 μm to 0.01 μm based on the Rpk parameter during 10 h. Following this period, the plasticity index decreased from an initial value of 1.1 to below 0.6, transitioning to a fully elastic contact stage, marking the onset of steady-state wear after 10 h. These results indicate that the reduction in surface roughness plays a crucial role in stabilizing wear behavior and provide insights into optimizing the long-term performance of ta-C:Si coatings in aqueous environments. Full article

The tribological behavior of molybdenum disulfide (MoS₂) coatings was systematically investigated under various controlled gas environments in a vacuum chamber. A hemispherical steel pin was slid cyclically over a MoS₂-coated steel disk, prepared via high-speed powder spraying. The study measured both dynamic and static friction coefficients under different gaseous atmospheres, including high vacuum, helium, argon, dry air, and water vapor. In high vacuum (10⁻⁵ Pa), an ultra-low dynamic friction coefficient (µ ≈ 0.01) was observed, while increasing values were recorded with helium (µ ≈ 0.03), argon (µ ≈ 0.04), dry air (µ ≈ 0.17), and water vapor (µ ≈ 0.30). Static friction coefficients followed a similar trend, decreasing significantly upon evacuation of water vapor or injection of inert gases. Surface analyses revealed that friction in vacuum or inert gases promoted smooth wear tracks and basal plane alignment of MoS₂ crystallites, while exposure to water vapor led to rougher, more disordered wear surfaces. Mass spectrometry and energetic modeling of physisorption interactions provided further insights into gas–solid interfacial mechanisms. These results demonstrate that the tribological performance of MoS₂ coatings is highly sensitive to the surrounding gas environment, with inert and vacuum conditions favoring low friction through enhanced basal plane orientation and minimal gas–surface interactions. In contrast, water vapor disrupts this structure, increasing friction and surface degradation. Understanding these interactions is crucial for optimizing MoS₂-based lubrication systems in varying atmospheric or sealed environments. Full article

Water-based drilling fluids (WBDFs) cannot be effectively applied in long horizontal wells, such as shale gas wells, due to their high coefficient of friction (COF) and filtration loss that can strongly limit the efficient and environmentally friendly development of oil and gas resources. The objective of this study is the formulation of a WBDF characterized by ultra-low friction and ultra-low filtration properties, with a high-concentration polyepoxysuccinic acid (PESA) solution being utilized in the continuous phase. The research aims at the exploration of the feasibility of the method, the validation of the results, and the elucidation of the underlying mechanisms. The experimental results confirmed that the proposed WBDFs have excellent rheological properties, a COF of 0.016 and an API filtration of 0.4 mL. Microscopic analysis confirmed a direct and positive correlation between the macroscopic properties of the drilling fluids and their adsorption behavior at high PESA concentrations. This approach can be used to redesign traditional WBDFs and provide new possibilities to realize super performance in WBDFs that can be used to replace oil-based drilling fluids. Full article

Hydraulic technology has been instrumental in the extensive application of offshore mechanical equipment, particularly in drilling platforms and ships, where high-performance hydraulic fluids are essential for safe and efficient operations. Addressing the urgent need for water-based hydraulic fluids as an alternative to traditional oil-based fluids, this study introduces a novel water-based hydraulic fluid fortified with phytic acid, derived from plant seeds, to achieve low biotoxicity, low coefficient of friction, and reduced frictional heat generation. The integration of phytic acid has significantly enhanced the lubricating performance, reducing the average coefficient of friction to as low as 0.013, as tested by the four-ball tester, which is the lowest value reported to date. Real-time monitoring of the temperature rise of the friction testing apparatus using an infrared thermal imager revealed a 78.6% reduction in temperature increase. Acute toxicity assays using Brine Shrimp demonstrated that the 96 h LC50 value for the water–glycol flame-resistant hydraulic fluid with added phytic acid exceeded 26,304 mg/L, indicating low toxicity. Characterization analyses elucidated the mechanisms underlying the improved tribological properties, highlighting the potential of this eco-friendly fluid for safe and efficient offshore operations. Full article

Fusion welding easily causes microstructural coarsening and tempering softening in the heat-affected zone (HAZ) of high-strength pipeline steel joints, which considerably deteriorates the strength and toughness. Here, X80 pipeline steel was subjected to friction stir welding (FSW), and external cooling was used to tailor the microstructure to optimize the strength–ductility combination of the nugget zone (NZ). Coarse granular bainite (GB) appeared at air cooling, whereas a fine ferrite/martensite microstructure was achieved at solid CO₂ cooling. The highest ratio of high-angle boundaries was obtained at solid CO₂ cooling because the variants were evenly distributed within the four close-packed (CP) groups. The low yield strength (YS) of 595 MPa was obtained in the NZ under air cooling, whereas a high YS of 755 MPa was achieved in the NZ under solid CO₂ cooling due to dislocation strengthening and fine-grain strengthening. Furthermore, an ultra-high tensile strength of 910 MPa and utilizable elongation of 15% were obtained in the NZ under solid CO₂ cooling, which was attributed to the fine effective grains and ferrite/martensite microstructure facilitating a ductile fracture. Full article

An ultra-low-power implantable body temperature sensor with a power consumption of 40.9 nW is presented. Deep body temperature measurement can be utilized for diseases such as inflammatory response due to implantable devices, treatment of traumatic brain injury, early monitoring of rejection after kidney transplantation, and monitoring of frictional heat in artificial joints, as well as health management such as ovulation cycles. Since it is implanted in the body and operated by a battery, it is very important to minimize power consumption. For low power consumption, we propose a dynamic virtual Wheatstone bridge technology for low-power transducer driving, and the simplified architecture is designed to operate at 0.6 V. The chip fabricated in a 180 nm CMOS process meets the ASTM E1112-00 specification for medical thermometers. That is, it can measure from 34 °C to 43 °C and meets the accuracy of ±0.1 °C between 37 °C and 39 °C. The measured power consumption at 37 °C is 40.9 nW. To verify practical application, a temperature sensor was implanted in a rat and body temperature changes before and after anesthesia were observed. Full article

The water-lubricated bearing plays a crucial role in the ship propulsion system, significantly impacting vessel safety. However, under the harsh working conditions of low-speed and heavy-load, the lubrication state of water-lubricated bearings is usually poor, leading to serious friction and wear. To improve the tribological performance of composites and reduce friction, three short fibers (ultra-high-molecular-weight polyethylene fibers, basalt fibers, and bamboo fibers) with the same mass fraction (5%) were added into the melted thermoplastic polyurethane (TPU). The tribological behavior of these three composites under different loads and rotation speeds was investigated using the CBZ-1 friction and wear tester. Through the comprehensive analysis of the friction coefficient, the wear mass loss, and the surface morphology, it was confirmed that the filled fiber positively affected the tribological performance of thermoplastic polyurethane materials. The experimental results indicated that basalt fiber significantly improved the tribological performance of TPU, and the friction coefficient of the sample was only 0.088 under the working conditions of 0.5 MPa and 250 r/min, which was 70.57% lower than that of pure TPU material. And in all the tests, the minimum wear of the basalt fiber-reinforced composite is only 0.4 mg, which is also the smallest of all the materials under all conditions, and a decrease of 98.69% compared to TPU. Under high loads, ultra-high-molecular-weight polyethylene fiber and bamboo fiber-reinforced composites have smoother surfaces and exhibit better tribological properties. This study provides an experimental foundation for tribological performance enhancement for environmentally friendly, water-lubricated bearing composites. Full article

In the field of industrial lubrication, solid–liquid composite lubrication (SLCL) techniques based on diamond-like carbon (DLC) coatings and lubricating oils are emerging recently, which may be applied in many fields in the near future, especially automotive industries. The tribological behaviors of SLCL systems depend strongly on the compatibility between DLC coatings and oils. This review describes the advantages of SLCL techniques by pointing out the synergistic effects between DLC coatings and lubricating oils. Then the main factors determining the tribological performance of SLCL systems are discussed in detail. Finally, a conclusion about the characteristics of reported SLCL systems is made, and a prospect about the potential development of SLCL technology is proposed. On the basis of the relevant literature, it could be found that the tribological properties of SLCL systems were influenced by many more factors compared with individual DLC lubrication or individual oil lubrication due to the complicated tribo-chemical reactions involving DLC and oil during friction. And under some optimized working conditions, the tribological performances of SLCL systems (friction and wear reduction) are superior to individual DLC lubrication and individual oil lubrication. However, the tribological performance of SLCL systems needs to be further improved (for example, to achieve superlubricity and ultra-low wear simultaneously) by adjusting the structures of DLC coatings, regulating the compositions of oils, and most importantly, enhancing the physicochemical and tribological synergies between DLC coatings and oils. This review provides a comprehensive understanding of the SLCL technology, which may be very helpful for the researchers and engineers in the field of industrial lubrication and tribology. Full article

The low viscosity of water-lubricated films compromises their load-bearing capacity, posing challenges for practical application. Enhancing the lubrication stability of these films under load is critical for the successful use of seawater-lubricated bearings in engineering. Polydopamine (PDA) shows great potential to address this issue due to its strong bio-inspired adhesion and hydration lubrication properties. Thus, PDA nanoparticles and seawater suspensions were synthesized to promote adhesive lubricating film formation under dynamic friction. The lubrication properties of PDA suspensions were evaluated on Cu ball and ultra-high molecular weight polyethylene (UHMWPE) tribo-pairs, with a detailed comparison to seawater. The results show PDA nanoparticles provide excellent adhesion and lubrication, enhancing the formation of lubricating films during friction with seawater. Under identical conditions, PDA suspensions demonstrated the lowest friction coefficient and minimal wear. At 3 N, friction decreased by 56% and wear by 47% compared to distilled water. These findings suggest a novel strategy for using PDA as a lubricant in seawater for engineering applications. Full article

This study highlights the impact of low amounts of MoS₂ quantities on composite performance by examining the effects of ultrasonication exfoliated MoS₂ at different loadings (0.1–0.5 wt%) on the mechanical and tribological parameters of epoxy composites. Even at low concentrations, the ultrasonication and exfoliation procedures greatly improve the dispersion of MoS₂ in the epoxy matrix, enabling its efficient incorporation into the tribofilm during sliding. Optimum mechanical properties were demonstrated by the MoS₂/epoxy composite at 0.3 wt%, including a modulus of elasticity of 0.86 GPa, an ultimate tensile strength of 61.88 MPa, and a hardness of 88.0 Shore D, representing improvements of 61.5%, 35.45%, and 16.21%, respectively. Corresponding tribological tests revealed that high sliding velocity (10 N load, 0.2 m/s) resulted in a 44.07% reduction in the coefficient of friction and an 86.29% reduction in wear rate compared to neat epoxy. The enhanced tribological performance is attributed to the efficient removal and incorporation of MoS₂ into the tribofilm, where it acts as a solid lubricant that significantly reduces friction and wear. Even though an ultra-low amount of filler concentration was added to the composite, a unique finding was the high MoS₂ content in the tribofilm at higher sliding speeds, enhancing lubrication and wear protection. This study establishes that even ultralow MoS₂ content, when uniformly dispersed, can profoundly improve the mechanical and tribological properties of epoxy composites, offering a novel approach to enhancing wear resistance. Full article

Ultra-high-strength steels have been considered an essential material for aviation components owing to their excellent mechanical properties and superior fatigue resistance. When machining these steels, severe tool wear frequently results in poor surface quality and low machining efficiency, which is intimately linked to the friction behavior at the tool–workpiece interface. To enhance the service life of tools, the adoption of efficient cooling methods is paramount. However, the understanding of friction behavior at the tool–workpiece interface under varying cooling conditions remains limited. In this work, both air atomization of cutting fluid (AACF) and ultrasonic atomization of cutting fluid (UACF) were employed, and their spray characteristic parameters, including droplet size distribution, droplet number density, and droplet velocity, were evaluated under different air pressures. Discontinuous sliding tests were conducted on the ultra-high-strength steel against cemented carbide and the effect of spray characteristic parameters on the adhesion friction coefficient was studied. The results reveal that ultrasonic atomization significantly improved the uniformity of droplet size distribution. An increase in air pressure resulted in an increase in both droplet number density and droplet velocity under both AACF and UACF conditions. Furthermore, the thickness of the liquid film was strongly dependent on the spray characteristic parameters. Additionally, UACF exhibited a reduction of 4.7% to 9.8% in adhesion friction coefficient compared to AACF. UACF provided the appropriate combination of spray characteristic parameters, causing an increased thickness of the liquid film, which subsequently exerted a positive impact on reducing the adhesion friction coefficient. Full article