Search Results (168)

Biodegradable composite materials enhanced with food waste for tribological applications are proposed in this article. Polymer materials used as matrices included polypropylene and polylactic acid, which, according to the manufacturers’ claims, were made entirely or partially from biodegradable raw materials. Additionally, the matrices were enhanced with three types of waste materials: powders derived from cherry and plum stones, and pomace extracted from flax seeds. The composites differed in the percentage content of filler (15 or 25 wt.%) and particle size (d < 400 µm or d > 400 µm). Thirty-minute block-on-ring friction tests were performed to determine frictional behaviour (when pairing with steel), and the wear mechanisms were analysed using optical microscopy and scanning electron microscopy, supplemented with Raman spectroscopy. A notable effect of cherry and plum stone fillers was observed as a reduction in motion resistance, as measured by the friction coefficient. This reduction was evident across all material configurations in polypropylene-based composites and was significant at the lowest concentrations and granulation in polylactic acid composites. The effect of flaxseed pomace filler was ambiguous for both composite bases. Full article

To promote the optimization of the anti-friction and anti-wear behavior of lightweight TiAl alloys, γ-TiAl-10 wt.% Ag self-lubricating composites were fabricated, and their mechanical and tribological properties were tested. The results showed that the silver in TiAl-10 wt.% Ag slightly reduced its mechanical properties compared with those of pure TiAl alloys. A silver-enriched lubrication film formed on a wear scar, which was helpful in improving the friction and wear behavior. It was found that a large amount of silver gathered at a wear scar, gradually spread out under the action of the sliding friction force, and then increased the silver distribution areas on the wear scar, leading to the good formation of a silver-rich film. Furthermore, an identification model was established to calculate the specific area η of the silver film. A quantitative relationship indicated that an increase in the Ag distribution area improved the tribological behavior of γ-TiAl-10 wt.% Ag. When the specific area η of a silver-rich film was maintained at 44–51%, the small friction coefficient (almost 0.28) and wear rate (about 2.25 × 10⁻⁴ mm³·N⁻¹·m⁻¹) were well stabilized. This provides a new research method to improve the tribological performance of TiAl-Ag samples. Full article

To investigate the temperature rise characteristics and tribological performance of angular contact ball bearings equipped with polymer-based self-lubricating retainers under oil-depleted conditions. PTFE-based composite retainers were fabricated using cold-press sintering technology. Comparative experiments on 7206C were conducted on three bearing configurations (domestic, imported NSK, and YSU-S1/S2 self-lubricating retainer bearing) using a dedicated fatigue tester under oil-depleted lubrication. This study demonstrates that angular contact ball bearings equipped with PTFE-based self-lubricating retainers exhibit superior thermal behavior under oil-depleted conditions. Compared to domestic and imported NSK bearings, the retainer-equipped bearing reduced equilibrium temperatures by 2~3 °C versus NSK/domestic bearings, with 60% lower peak temperatures. The high speed further facilitates the formation of transfer films, resulting in a smoother raceway and notably enhancing the bearing’s temperature rise characteristics. This study establishes a material–process–performance framework, bridging polymer composites and industrial bearing design. Full article

This study investigates the influence of the HfB₂ content and sintering method on the mechanical behavior of Ti₂AlC-based composites. Compositions containing 0–10 wt.% HfB₂ are processed via conventional and microwave sintering at 1200 °C for 30 min. X-ray diffraction and scanning electron microscopy analyses have confirmed the formation of the Ti₂AlC and HfB₂ phases, whereas the TiC phase is predominantly observed in samples processed by conventional sintering. The highest hardness (~475 HV) and compressive strength (~450 MPa) are that of the composite containing 5 wt.% HfB₂ associated with a porosity reduction of approximately 10%. These improvements are attributed to the enhanced densification and microstructural refinement achieved via microwave processing. The findings underscore the potential of HfB₂ addition and microwave sintering in tailoring the structure–property relationships of the Ti₂AlC composites, enabling applications at high-temperature filtration, thermal barriers, and self-lubricating components. Full article

Poly(phenylene sulfide) (PPS) is a high-performance thermoplastic engineering material with excellent comprehensive performance that finds application in many fields due to its good processability, excellent heat resistance, and mechanical properties. However, the poor friction and wear properties of PPS limit its wide application in industrial sectors. In this work, polytetrafluoroethylene (PTFE) was adopted as the solid tribo-modifier to improve the tribological performance of PPS. The efficacy of using three types of PTFE fillers, namely PTFE fiber, micropowder, and nanopowder, was comparatively investigated. The results revealed that the incorporation of PTFE was beneficial to improving the tribological properties of PPS and PTFE nanopowders, which were prepared by irradiation treatment technology that demonstrated the best modification effect in terms of both tribological and mechanical performance among the studied systems. In addition, the coefficient of friction and specific wear rate of PPS composites with 30 wt% nanopowders reached 0.165 and 3.59 × 10⁻⁵ mm³/Nm, respectively, which were 70.7% and 99.0% lower than their pure PPS counterparts. The above finding was attributed to the improved compatibility between the PTFE nanopowders and the PPS substrate as well as the easier formation of intact PTFE transfer film on the contact surface. This work shows some perspective for designing self-lubricating polymer composites that broaden their application in industrial sectors. Full article

A novel composite groove array surface was fabricated using femtosecond laser ablation technology to enhance self-replenishment capability. Initially, the driving efficiency of droplets on the composite groove array surface was tested using a high-speed droplet transportation system, characterizing the effect of this surface on lubricant backflow characteristics. Simultaneously, measurement of lubricating film thickness was utilized to explore the lubrication enhancement effect of the composite groove array surface on oil film formation under reciprocating motion. The multidimensional gradient wettability, engineered through the composite groove array surface, demonstrated excellent efficiency in lubricant replenishment within the lubrication track. Oil droplet transportation testing demonstrated that the composite groove array surface, which induced gradient wettability at the boundary, attained a maximum driving speed of 123.5 mm/s. This innovative design significantly reduced the barriers associated with lubricant backflow, particularly those induced by cavitation expansion during high-frequency reciprocating motion. Furthermore, the results demonstrated that the film-forming capabilities of this composite groove array surface were enhanced, thereby optimizing the overall lubrication performance. Full article

With the aim of developing a wear-resistant ultraviolet (UV)-cured self-lubricating coating, this study investigated the impact of matrix components and lubricants on UV-cured interpenetrating polymer network-polyurethane acrylate (IPN-PUA) self-lubricating coatings. Four coatings with different monomer combinations were prepared, using isophorone diisocyanate (IPDI) or tolylene-2,4-diisocyanate (TDI) in combination with hydroxypropyl acrylate (HPA) or 2-hydroxyethyl acrylate (HEA). These coatings were denoted as IPDI-HPA, IPDI-HEA, TDI-HPA, and TDI-HEA, respectively. The surface morphologies, compositions, friction and wear properties, as well as the comprehensive performances were investigated. The results indicated that IPDI-HPA had the lowest surface roughness and that TDI-HEA had the smallest wear rate, while TDI-HPA showed the best overall performance (roughness of 1.485 μm, coefficient of friction (COF) of 0.746, and wear rate of 10.64 × 10⁻¹⁴ m³/N·m). With TDI-HPA as the matrix, graphite and polytetrafluoroethylene (PTFE) particles of different sizes were added as lubricants. The T-P-25F (TDI-HPA coating with 25 μm sized PTFE) coating had self-lubricating capabilities, as was manifested by a friction coefficient of 0.395, which was 47% lower than that of the pure TDI-HPA coating, and it simultaneously showed outstanding wear-resistance performance. The wear rate of the T-P-25F coating was 3.97 × 10⁻¹⁴ m³/N·m, 62.7% lower than that of the pure TDI-HPA coating. This research provides valuable guidance for optimizing the performance of such coatings and yields a self-lubricating coating with excellent wear resistance. Full article

This study aims to enhance the wear resistance of MAO/MoS₂ composite coatings fabricated on TC4 titanium alloy substrates through a composite process of microarc oxidation (MAO) and hydrothermal synthesis. The MAO treatment experiments were designed according to the L16 (4⁵) orthogonal array to optimize the NaAlO₂ concentration and electrical parameters (oxidation voltage, frequency, duty ratio, and treating time), with four levels for each factor. The optimized MAO process parameters were identified as a NaAlO₂ concentration of 10 g/L, an oxidation voltage of 500 V, a frequency of 200 Hz, a duty ratio of 20%, and a treating time of 30 min. The experimental results indicated a notable reduction in porosity, from 4.45% to 0.30%, in the optimized composite coating. Concurrently, there was a 43.2% increase in microhardness and a 327.9% increase in adhesive strength. Furthermore, the average coefficient of friction (CoF) of the composite coating was observed to be 0.13 at a high load of 20 N and a wear time of 20 min, representing a significant reduction of 68.5% compared to the CoF of the single MAO coating. Full article

Obtaining robust power density through piezoelectric nanogenerators (PENGs) is very challenging. Challenges include achieving good mechanical stability, optimum stiffness, reasonable voltage generation, limited heat dissipation, and power density as needed. This work focused exactly on these areas, and hybrid filler emerged as a promising candidate among the composites studied. For example, hybrid fillers exhibited optimized properties suitable for self-powered engineering applications. The composites fabricated in this work were based on titanium oxide (TiO₂), molybdenum disulfide (MoS₂), and silicone rubber (SR) as a host matrix. The results showed that TiO₂ represents a good reinforcing filler, while MoS₂ exerts a lubricating effect, improving the composites’ mechanical strength and elongation at break. For example, the compressive modulus at 8 per hundred parts of rubber (phr) was 2.39 MPa (TiO₂), 1.62 MPa (MoS₂), and 2.1 MPa (hybrid filler). Similarly, the hysteresis loss at 5 phr was 20.09 J/m (TiO₂), 21.56 J/m (MoS₂), and 20.48 J/m (hybrid filler). Moreover, the elongation at break at 8 phr was 150% (TiO₂), 194% (MoS₂), and 170% (hybrid filler). In the same way, the electro-mechanical properties obtained were also robust. For example, the voltage output was ~22 mV (TiO₂), ~35 mV (MoS₂), and ~46 mV (hybrid filler). Moreover, the PENGs developed in this work generated power. For example, the power density was ~0.55 pW/cm² (TiO₂), ~1.03 pW/cm² (MoS₂), and ~1.56 pW/cm² (hybrid filler). Finally, the piezoelectric coefficient of the PENGs was 40 pC/N (TiO₂), 112 pC/N (MoS₂), and 160 pC/N (hybrid filler). These materials have a promising role in energy harvesting through self-powered nanogenerators for portable electronic systems. Finally, the low-power PENGs developed provide cost-effective voltage and power management circuits. This allows these PENGs to contribute to sustainable and self-sufficient electronic systems like pacemaker implants. Full article

In this work, powder metallurgy was used in order to produce self-lubricating composite materials. The NiCrSiB alloy as a matrix of the sinters and 20 wt. % CaF₂ as a solid lubricant were used. The sinters were subjected to wear tests using the pin-on-disc method at four different temperatures (room temperature (RT), 200, 400, and 600 °C). The coefficients of friction of the friction pairs were determined, and research on their wear mechanism was carried out. For this purpose, research techniques such as Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), and profilometer were used. Based on the conducted tests, it was found that CaF₂ was smeared on the surfaces of the samples and counter-specimens, particularly at elevated temperatures. Moreover, it was found that micro-cutting and micro-ploughing are the major wear of the friction pairs at room temperature, while with the increasing temperature, they were dominated by the reduction of such mechanisms, which is associated with the formation of a tribofilm composed of CaF₂ and oxidation wear. Full article

Polymer composite coatings exhibit excellent mechanical properties, chemical resistance, and self-lubricating characteristics, providing an effective solution to address the failure of transmission components under harsh operating conditions, including high-speed, high-pressure, and oil-deficient environments, which often lead to excessive friction and limited bearing performance. This study fabricated three polyamide-imide (PAI) composite coatings modified with monodisperse surface-modified nano-silica (SiO₂) via direct spraying and compared their physicochemical parameters. The tribological performance of the three coatings was evaluated using ring-block high-speed friction and wear tester under continuous loading conditions. The tests were conducted using diesel engine oil CI4-5W40, supplemented with oil-soluble cerium dioxide (CeO₂) nanoparticles as an energy-efficient and restorative additive, as the lubricating medium. The experimental results demonstrated that the PAI composite coating exhibited a load-bearing capacity exceeding 1000 N (66 MPa). The wear mechanism analysis reveals that CeO₂ nanoparticles embedded in the coating surface form a cobblestone-like protective layer. This unique microstructure compensates for the surface pits generated by PAI matrix transfer and minimizes direct contact between the coating and steel ring. Additionally, the synergistic interaction between short carbon fiber (SCF) and the tribofilm contributes to the exceptional tribological properties of the coating, including coefficients of friction as low as 0.04 and wear rates below 0.41 × 10⁻⁸ mm³/N·m. The experimental findings could provide an experimental and theoretical foundation for the application of coatings under conditions involving finished lubricants. Full article

Hardness and wear resistance are the requirements of nickel-based superalloys used in gas turbine blades. This study uses laser cladding technology to develop three types of wear-resistant coatings—NiCr-2%hBN, NiCr-12%cBN, and NiCr-2%hBN-12%cBN—on GTD-111 superalloy. The above coatings’ microstructure, microhardness, and tribological behavior were systematically characterized by scanning electron microscope, hardness tester, pin-on-disc wear device, and three-dimensional profiles. The hardness test results showed that the hBN coating has the lowest hardness (692 HV) due to its layered structure, and the hBN-cBN coating has the highest hardness (992 HV) due to its complex structure and the creation of inhomogeneous nucleation centers in the coating. The wear test results showed that the hBN coating has a lower coefficient of friction (COF) (0.49) than the hard cBN coating (0.53) due to its lubricating properties. Meanwhile, the wear rate of the hBN coating is lower than the wear rate of the hard cBN due to the weak forces of one in the B-N bond. However, the wear test results of hBN-cBN coating showed that the effects of hBN and the high hardness of cBN cause the formation of a coating with the lowest wear rate (0.22 × 10⁻⁶ mm³/N·m), COF (0.41), fluctuation, wear depth (17.2 µm), and wear volume loss (0.32 × 10⁵ µ³) compared to the other two coatings. In addition, in the hBN-cBN coating, due to the greater driving force for the inhomogeneous nucleation of the melt, a larger area of equiaxed grains was formed, which in turn had a significant effect on increasing the wear resistance. Full article

Reducing friction-induced squeal noise is a common issue in daily life and industrial production, particularly for elastomers. However, adjusting structure and wettability in wet environments to solve the friction-induced squeal noise remains a challenge. Here, inspired by rabbit corneas, a microchannel nanofiber array composite structure superhydrophilic elastomer material was prepared to achieve rapid liquid spreading and optimize liquid distribution. Researchers have found that when the depth of the groove microchannel is 400 μm and the length of the nanofiber is 5000 nm, water rapidly spreads on the surface in only 430 ms. This reduces self-excited vibration caused by friction, thereby reducing squealing noise by 20 decibels (dB). This article proposes a novel and direct biomimetic squealing noise reduction strategy, which has great potential in solving friction vibration noise problems in industry and daily life, such as automotive wiper blades, engines, oil lubricated bearings, etc. Full article

To significantly improve the tribological performance of epoxy resin (EP), a novel h-BN/MoS₂ composite was successfully synthesized using spherical MoS₂ particles with lamellar self-assembly generated through the calcination method, followed by utilizing the “bridging effect” of a silane coupling agent to achieve a uniform and vertically oriented decoration of hexagonal boron nitride (h-BN) nanosheets on the MoS₂ surface. The chemical composition and microstructure of the h-BN/MoS₂ composite were systematically investigated. Furthermore, the enhancement effect of composites with various contents on the frictional properties of epoxy coatings was studied, and the mechanism was elucidated. The results demonstrate that the uniform decoration of h-BN enhances the chemical stability of MoS₂ in friction tests, and the MoS₂ prevents oxidation and maintains its self-lubricating properties. Consequently, due to the protective effect of h-BN and the synergistic interaction between h-BN and MoS₂, the 5 wt % h-BN/MoS₂ composite exhibited the best friction and wear resistance when incorporated into EP. Compared to pure EP coatings, its average friction coefficient and specific wear rate (0.026 and 1.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹, respectively) were significantly reduced. Specifically, the average friction coefficient decreased by 88% and the specific wear rate decreased by 99%, highlighting the superior performance of the h-BN/MoS₂-enhanced epoxy composite coating. Full article

Additive manufacturing technology has the advantages of precise manufacturing, high levels of customization, and large-scale molding; it can achieve the design of complex geometric structures and structural/functional integrated components, which is difficult to realize using traditional manufacturing technology, especially for different tribological applications. Ceramic materials are widely used in industries such as high-end manufacturing in aviation, aerospace, energy, and biomedicine due to their excellent wear resistance, high temperature stability, and hardness. The tribological properties of ceramic parts determine their versatility and durability during the application process. The rise of additive manufacturing technology in the field of ceramics has opened up the possibility of creating ceramics with excellent friction and wear properties and overcoming the limitations of traditional manufacturing processes. Although several studies on 3D printing of wear-resistant/self-lubricating metal- or polymer-based parts have been published, there has until now been no comprehensive review of additive manufacturing of advanced structural ceramics and composites for the purpose of reducing friction and enhancing wear-resistant properties. This article discusses the currently used ceramic additive manufacturing technology and processes, the ceramic materials used in the field of tribology, and how the combination of these two can improve the tribological properties of ceramic components from the perspective of micro- and macrostructures. Finally, specific tribological applications of additively manufactured ceramics in various industrial and biomedical fields are also introduced. Full article