Search

Composite coatings with solid lubricants can improve the tribological performance of aluminum alloy parts prepared by Laser Powder Bed Fusion (LPBF). In this study, Ni-MoS2 self-lubricating composite coatings were one-step prepared on additive manufactured aluminum alloy surface via jet electrodeposition. The properties and lubrication performance of the coatings prepared using composite electrolyte with different MoS2 particle diameters and concentrations were investigated. The lubrication mechanism of the composite coating was discussed. The results showed that 0.8 μm MoS2 had less agglomeration than 80 nm, resulting in a uniform surface. The lubrication performance of the composite coating was affected by MoS2 particles content and coating hardness. With the increase of MoS2 concentration in the composite electrolyte, the friction coefficient and wear rate decreased, and achieved the best lubrication performance of 0.12 friction coefficient and 0.11 mg/m wear rate when MoS2 composite electrolyte is 5 g/l and MoS2 is 0.8 μm. However, the addition of soft MoS2 decreased the coating hardness, lower hardness will cause lubrication failure. [ABSTRACT FROM AUTHOR]

Abstract The ball bearing market is mature where there is a massive range of products available with new ones being developed all the time due to technological advancements. Additive Manufacturing (AM) provides a promising approach for developing oil-impregnated ball bearings. Oil impregnated bearings are critical for applications requiring smooth and low-friction motion. This study explores the feasibility of utilizing laser powder bed fusion (LPBF) technology to fabricate 304 stainless steel (304SS) samples with open pores, which can then be impregnated with a lubricant. To achieve this, 304SS powder was used, and optimum selective laser melting (SLM) printing parameters were altered to induce intentional pores. Initial screening of samples involved Archimedes density measurements and computed tomography (CT) scanning was conducted on a selected samples to assess their porosity levels. CT scan foam analysis results indicated a correlation between hatch spacing and porosity. Results revealed trends in cell volume and solidified scanning tracks thickness, indicating greater connectedness with larger pores. Synthesis of these findings could help in the development of efficient and reliable open pores that may find use in oil-impregnated self-lubricating ball bearings.

Yttria-stabilized zirconia and flake graphite c omposite (C/YSZ) coatings were successfully prepared on a TC4 substrate by electrophoretic co-deposition and sintering at 1100 °C using YSZ nanopowder and flake graphite. The effects of the graphite content on the microstructure and friction-wear properties were investigated. The results indicated that flake graphite agglomerated in the C/YSZ coating. The YSZ coating with 0.6wt.% graphite exhibited the highest toughness with the plastic resistance index (H/E) of 0.0172, which was 6.8 % higher than that of the YSZ coating, and effectively inhibited the formation of coating cracks. However, an increase or a decrease in the graphite content led to a decrease in the toughness of the C/YSZ composite coating. The agglomerated graphite in the C/YSZ composite coating acted as a solid lubricant and affected friction and wear properties. The coefficient of friction (COF) of the 0.6C/YSZ sample was 0.45, which was 40 % lower than that of the YSZ sample. The reason for this was that graphite effectively inhibited the falling-off of debris from the coating surface and reduced abrasive wear. However, an excessive amount of graphite, i.e., in case of the 0.8C/YSZ coating, decreased the roughness of the wear surface, leading to a reduction in the H/E and COF by 24.4 % and 29.7 %, respectively. [ABSTRACT FROM AUTHOR]

Globally, osteoarthritis (OA) is the most prevalent joint disease and is characterized by infiltration of M1 macrophages in the synovium, anabolic–catabolic imbalance of the extracellular matrix (ECM), increased articular shear force and overproduction of reactive oxygen species (ROS). Disease-modifying OA drugs are not yet available, and treatments for OA focus solely on reducing pain and inflammation and have limited therapeutic effect. Herein, we developed an injectable self-lubricating poly(N-acryloyl alaninamide) (PNAAA) hydrogel loaded with platelet lysate (PL) (termed "PNAAA@PL") for treating OA. Tribological and drug release tests revealed suitable lubrication properties and sustained release of bioactive factors in PNAAA@PL. In vitro experiments showed that PNAAA@PL alleviated interleukin-1β (IL-1β)-induced anabolic–catabolic imbalance of chondrocytes and repolarized pro-inflammatory M1 macrophages to the anti-inflammatory M2 phenotype via intracellular ROS scavenging. Additionally, the PNAAA@PL hydrogel enhanced the migratory capacity and chemotaxis ability of stem cells, which are essential for chondrogenesis. In vivo , the functionalized PNAAA@PL hydrogel acted like synovial fluid following intra-articular injection into a rat OA model with anterior cruciate ligament transection, ultimately attenuating cartilage degeneration and synovitis. According to molecular mechanism studies, PNAAA@PL repairs cartilage in the OA model by inhibiting the NF-ĸB pathway. Overall, this self-lubricating PNAAA@PL hydrogel offers a comprehensive strategy for preventing OA progression by engineering a biophysiochemical microenvironment to generate high-quality hyaline cartilage. [Display omitted] • Loading platelet lysate on hydrogels can delay the release of bioactive factors. • PNAAA@PL hydrogel attenuated joint degeneration by remodeling joint microenvironment. • Differentially expressed genes contributed to anti-OA abilities of PNAAA@PL hydrogel. • The synergy of lubrication and sustained bioactive factors delivery help treat OA. [ABSTRACT FROM AUTHOR]

The reduced graphene oxide-Cu self-lubricating composites with short carbon fiber fillers were fabricated by powders wet-mixing combined with hot-pressed sintering process. The impacts of short carbon fiber content on microstructure, mechanical and tribological performance of reduced graphene oxide-Cu composites were characterized. The reduced graphene oxide/carbon fiber hybrid fillers were randomly distributed in the sintered bulk compacts. The hybrid filled composites achieved enhancement in mechanical and tribological properties. With increasing carbon fiber content, hardness and compressive yield strength of the prepared composites were increased, and both friction coefficient and wear rate showed a constant decrease trend under different loads. Owing to the synergy effect of reduced graphene oxide/carbon fiber hybrid lubricant fillers during sliding together with the greatly enhanced hardness and yield strength, up to 0.6 wt% carbon fiber incorporation resulted a lowest friction coefficient and decreased wear rate. Randomly distributed reduced graphene oxide/carbon fiber hybrid fillers provided the lubrication to reduce friction and wear for Cu matrix. [ABSTRACT FROM AUTHOR]

The ball bearing market is mature where there is a massive range of products available with new ones being developed all the time due to technological advancements. Additive Manufacturing (AM) provides a promising approach for developing oil-impregnated ball bearings. Oil impregnated bearings are critical for applications requiring smooth and low-friction motion. This study explores the feasibility of utilizing laser powder bed fusion (LPBF) technology to fabricate 304 stainless steel (304SS) samples with open pores, which can then be impregnated with a lubricant. To achieve this, 304SS powder was used, and optimum selective laser melting (SLM) printing parameters were altered to induce intentional pores. Initial screening of samples involved Archimedes density measurements and computed tomography (CT) scanning was conducted on a selected samples to assess their porosity levels. CT scan foam analysis results indicated a correlation between hatch spacing and porosity. Results revealed trends in cell volume and solidified scanning tracks thickness, indicating greater connectedness with larger pores. Synthesis of these findings could help in the development of efficient and reliable open pores that may find use in oil-impregnated self-lubricating ball bearings. [ABSTRACT FROM AUTHOR]

Highlights The improvement in social production efficiency demands increasingly faster mechanical operation speeds. However, under high‐speed friction conditions, the frictional heat generated by nylon 6 (PA6) components is difficult to dissipate efficiently, leading to severe wear and subsequently threatening the safe operation of the equipment. In this work, interconnected expanded graphite/stearic acid (EG/SA) networks in PA6 composites were constructed to achieve fast frictional heat dissipation and self‐lubricating properties by a simple hot‐pressing method. The synergistic lubrication of EG and SA results in PA6 composites with a low coefficient of friction (COF) of 0.12, a 74.5% reduction compared to pure PA6. The low COF reduces the generation of frictional heat, while the conduction and absorption of frictional heat by the EG/SA network accelerates the dissipation of frictional heat, ultimately lowering the contact temperature from 106.9°C to 40.6°C. The specific wear rate of the PA6 composite is as low as 1.7 × 10−5 mm3 N−1 m−1, which is 90.1% lower than that of pure PA6. This study provides a new solution for the rapid dissipation of frictional heat in polymer composites under harsh operating conditions and broadens the application range of wear‐resistant polymer composites. Expanded graphite (EG) prevents stearic acid from leaking through adsorption. The interconnected EG network transfers frictional heat to stearic acid. The phase transition of stearic acid can absorb heat and promote lubrication. The low COF and high heat dissipation make PA6 composites highly wear‐resistant. [ABSTRACT FROM AUTHOR]

Highlights The Stirling engine is a high‐efficiency externally heating piston engine. The self‐lubricating properties of polytetrafluoroethylene (PTFE) are crucial for the operation of Stirling engines. Three PTFE composites filled with different contents of carbon fiber (CF), polyimide (PI) and nano‐zirconia (nano‐ZrO2) were prepared and their mechanical, friction and wear properties were investigated. The results showed that the density of CF‐containing PTFE composites was significantly reduced by 1.46% to 6.9% compared to neat PTFE. Meanwhile, the incorporation of fillers greatly enhanced the hardness by more than 21.4% over the hardness of neat PTFE. In addition, the friction coefficients of three PTFE composites were lower than those of neat PTFE, and the wear rate of these composites was three orders of magnitude lower than that of neat PTFE. In particular, the wear rate of PTFE filled with CF and PI at high pressure (2 MPa) and high velocity (4 m/s) was only 1.24 × 10–6 mm3/Nm. The wear morphology was also analyzed by scanning electron microscopy and energy‐dispersive x‐ray spectroscopy. It was found that the addition of CF and PI in PTFE has the most pronounced improvement on tribological performances. The synergistic effect of CF's mechanical reinforcement and PI's adhesive properties reduces the wear of the matrix, resulting in excellent wear resistance of PTFE composites. The compressive strength of PTFE was reinforced by CF and nano‐ZrO2. CF can lower the density and significantly enhance hardness of PTFE. Synergistic CF and PI enhance PTFE composites' friction & wear performance. Adhesive fillers & debris size key to forming uniform continuous transfer films. [ABSTRACT FROM AUTHOR]

MAX phase ceramics is a large family of nanolaminate carbides and nitrides, which integrates the advantages of both metals and ceramics, in general, the distinct chemical inertness of ceramics and excellent physical properties like metals. Meanwhile, the rich chemical and structural diversity of the MAXs endows them with broad space for property regulation. Especially, a much higher self‐lubricity, as well as wear resistance, than that of traditional alloys and ceramics, has been observed in MAXs at elevated temperatures in recent decades, which manifests a great application potential and sparks tremendous research interest. Aiming at establishing a correlation among structure, chemical composition, working conditions, and the tribological behaviors of MAXs, this work overviews the recent progress in their high‐temperature (HT) tribological properties, accompanied by advances in synthesis and structure analysis. HT tribological‐specific behaviors, including the stress responses and damage mechanism, oxidation mechanism, and wear mechanism, are discussed. Whereafter, the tribological behaviors along with factors related to the tribological working conditions are discussed. Accordingly, outlooks of MAX phase ceramics for future HT solid lubricants are given based on the optimization of present mechanical properties and processing technologies. [ABSTRACT FROM AUTHOR]

Smart polymeric coatings play a crucial role in protecting steel surfaces from corrosion and wear. One of progressive smart behavior is self-healing behavior especially in self-healing epoxy coatings. Creating or improving the second smart behavior is known as a new trend for these smart materials. This study aims to investigate the effects of ZrO 2 nanoparticles on the self-lubricating behavior as the second smart behavior of the linseed oil-loaded microcapsule/epoxy composite coatings. To do so, the in-situ polymerization method was used for the synthesis of linseed oil-loaded microcapsule. Results showed that the average size of prepared linseed oil-loaded microcapsules was 563 nm. The composite coatings were prepared by different content of ZrO 2 nanoparticles (0, 3, 6, 9, 12, and 15 wt%) and constant content of linseed oil-loaded microcapsules (5 wt%). The tribological performance of samples was studied using pin-on-disk test. The worn surface of the samples was also studied using field emission scanning electron microscope (FESEM) images. Results proved that the frictional coefficient and wear rate of the samples were significantly decreased by increasing the concentrations of the ZrO 2 nanoparticles up to 9 wt%. The lowest friction coefficient and wear rate values of 0.085 and 0.142 × 10−6 mm3/Nm were obtained for 5 wt% linseed oil-loaded microcapsules/epoxy with 9 wt% ZrO 2 which were about 82 % and 88 % lower than those of pure epoxy coating. [ABSTRACT FROM AUTHOR]

In engineering applications, it is crucial to extend service life by reducing the coefficient of friction (COF) and wear rate to improve dry wear resistance. This work investigates the tribological properties of NiCrAlY-Cr3C2-Ti2SnC coatings with different Ti2SnC additions over a wide temperature range. Composite coatings with varying Ti2SnC concentrations were deposited onto TC4 titanium alloy substrates using atmospheric plasma spraying. Pin-on-disk wear tests were utilized to evaluate the tribological performance of the coatings, including the friction coefficient and wear rate, from room temperature to 800 °C. The wear mechanism of the coating was determined using SEM and a 3D profiler. The results demonstrate that the coating containing 30 wt.% Ti2SnC (NC-30TSC) exhibits the lowest friction coefficient (0.29) and wear rate (4.89 × 10−5 mm3·N−1·m−1) at 800 °C. The composite coatings containing Ti2SnC exhibited a decreased coefficient of friction and wear rate due to the high-temperature decomposition products of Ti2SnC, such as TiO2 and TiC. The wear mechanisms of the NC-30TSC coating were adhesive and fatigue wear at 300 °C, adhesive and oxidation wear at 600 °C, and oxidation wear at 800 °C. Additionally, the prefabricated cracks on the surface of the NC-30TSC coating healed after isothermal treatment, demonstrating excellent self-healing performance. [ABSTRACT FROM AUTHOR]

In response to the persistent challenge of optimizing the tribological performance of engineered coatings without compromising material hardness, this study investigates the potential of medium-entropy CrCoNiCu alloy films. Fabricated via sputtering and subsequently aged at 200 °C for 24 h, these films are examined for their mechanical and tribological behaviors through nanoindentation and reciprocal sliding wear tests. The primary result reveals that the sputtering fabrication yields a single face-centered cubic phase enriched with stacking faults and twins due to a vapor quenching and an increase in defective nuclei formation. The aging treatment uniquely facilitates the formation of Cu-rich phases, featuring repetitive plate-like structures along twin boundaries, by altering diffusion pathways to enhance diffusivity at the applied low temperature. Remarkably, this process not only increases the hardness of the films by 1.5 GPa but also leads to significant improvements in their tribological performance, with reductions in friction coefficients and wear volumes by 12.1% and 90.1%, respectively. The tribological properties originate with the synergistic effects of precipitation hardening and the lubricating layer inducing the reduction of abrasive wear and inhibition of direct contact between sliding surfaces. These findings illuminate that the CrCoNiCu alloy exhibits an exceptional capacity for superior wear resistance at soft metals, offering a compelling strategy to navigate the traditional trade-off between wear rate and hardness in the design of advanced engineering materials.

Wind power gears will be excessively worn due to lubrication failure during operation. Herein, the tribological properties of rubbing pairs are improved by filling solid lubricants into surface texture. In texture design, three types of topological textures (Circle (C), Hexagon (H) and Circle/Hexagon (CH)) were obtained by cell topology optimization, and then three cases with 20%, 30%, and 40% density were designed for each texture. Next, SnAgCu and TiC were deposited in texture of AISI 4140 steel (AS) to obtain 9 kinds of self-lubricating surfaces. Among them, AS with 30% CH density (AS-CH30) exhibits excellent mechanical and tribological properties. Compared with AS-C and AS-H, the maximum equivalent stress of AS-CH was decreased by 10.86% and 5.37%, respectively. Friction coefficient and wear rate of AS-CH30 were 79.68% and 78% lower than those of AS. The excellent tribological performances of AS-CH30 can be attributed to the synergistic effect of topological surface and solid lubricants. Topological surface can not only reduce fluctuation of equivalent stress, but also promote the stored lubricants to be easily transferred at the contact interface to form a 200 nm lubricating film containing solid lubricants (mainly), oxides and wear debris. [ABSTRACT FROM AUTHOR]

Abstract MAX phase ceramics is a large family of nanolaminate carbides and nitrides, which integrates the advantages of both metals and ceramics, in general, the distinct chemical inertness of ceramics and excellent physical properties like metals. Meanwhile, the rich chemical and structural diversity of the MAXs endows them with broad space for property regulation. Especially, a much higher self‐lubricity, as well as wear resistance, than that of traditional alloys and ceramics, has been observed in MAXs at elevated temperatures in recent decades, which manifests a great application potential and sparks tremendous research interest. Aiming at establishing a correlation among structure, chemical composition, working conditions, and the tribological behaviors of MAXs, this work overviews the recent progress in their high‐temperature (HT) tribological properties, accompanied by advances in synthesis and structure analysis. HT tribological‐specific behaviors, including the stress responses and damage mechanism, oxidation mechanism, and wear mechanism, are discussed. Whereafter, the tribological behaviors along with factors related to the tribological working conditions are discussed. Accordingly, outlooks of MAX phase ceramics for future HT solid lubricants are given based on the optimization of present mechanical properties and processing technologies.

Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated laser-induced reduced graphene oxide/hexagonal boron nitride (L-rGO/h-BN) was introduced as an additive into a silicon nitride matrix, then a silicon nitride/reduced graphene oxide/hexagonal boron nitride (Si3N4/L-rGO/h-BN) ceramic composite was successfully synthesized using Spark Plasma Sintering technology. This approach led to enhancements in both the mechanical and self-lubricating properties of silicon nitride ceramics. This is due to the good monodispersity of the incorporating graphene in the silicon nitride matrix. The flexural strength and fracture toughness of the ceramic composite experienced notable increases of 30.4% and 34.4%, respectively. Tribological experiments demonstrate a significant enhancement in the self-lubricating performance of ceramic composites upon the incorporation of L-rGO/h-BN. The coefficient of friction and wear spot diameter experienced reductions of 26.6% and 21%, respectively. These improvements extend the potential industrial applications of Si3N4/L-rGO/h-BN ceramic composites. Throughout the friction process, the evenly exposed rGO and h-BN demonstrate an effective self-lubricating effect on the wear surface. This research paves the way for a novel approach to fabricating high-performance self-lubricating structural ceramics. [ABSTRACT FROM AUTHOR]

Titanium alloy is an essential material for preparing aerospace engines because of its excellent performance. However, the poor wear resistance of titanium alloy restricts its further development as a critical engine material. This study aimed to use laser cladding and particle enhancement technologies to enhance the surface wear resistance of titanium alloy. (NiCoCr) 94 Al 3 Ti 3 +hBN, (NiCoCr) 94 Al 3 Ti 3 +cBN, and (NiCoCr) 94 Al 3 Ti 3 +hBN + cBN were prepared on the surface of titanium alloy, and the wear resistance mechanism of single-phase self-lubricating particles, single-phase hard particles, and self-lubricating and hard biphasic particles was investigated. The results showed that the microhardness of the biphase-reinforced coating was 1083.8 HV0.5, which was higher than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 368.4 HV0.5 and 149.8 HV0.5, respectively. The friction coefficient of the biphase-reinforced coating was 0.4208, which was lower than that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating by 0.0224 and 0.0686, respectively. The wear rate of the biphase-reinforced coating was 0.076 mm3/NM, and the wear resistance of the biphase-reinforced coating was 3.42 and 1.37 times that of the self-lubricating particle-reinforced coating and hard-particle-reinforced coating, respectively. hBN relied on its own decomposition to promote the coating to present a layered unstable structure to achieve a wear reduction effect, cBN relied on its own hardness to resist wear and played a wear-resistant role, whereas biphase-reinforced coating had a hard wear resistance and formed a lubricating film to enhance the wear resistance of the coating. The comprehensive performance of the dual-phase wear-resistant coating reinforced by hard particles and self-lubricating particles was better than that of single-phase wear-resistant coating, providing a reference for developing wear-resistant coating integrating hardness and self-lubrication. [ABSTRACT FROM AUTHOR]

The manuscript presents the synthesis and dry sliding wear performance of Al7075 alloy‐based composites. Five compositions namely Al7075 alloy, Al7075+3 vol % molybdenum disulfide, Al7075+3 vol % molybdenum disulfide+3 vol % zirconium diboride, Al7075+3 vol % molybdenum disulfide+6 vol % zirconium diboride and Al7075+3 vol % molybdenum disulfide+9 vol % zirconium diboride were stir cast and characterized for hardness, x‐ray diffraction, microstructure, and tribological properties. In‐situ formed zirconium diboride particles increase the hardness of Al7075 alloy whereas molybdenum disulfide shows the opposite trend due to its self‐lubricating nature. X‐ray diffraction analysis identifies subsequent phase particles in the matrix while microstructural images exhibit the dispersion and morphology of reinforcement particles. The wear tests and friction coefficient were analyzed with variations of sliding velocity, normal load, sliding distance, and compositions. Further, the obtained wear results were also correlated with microstructure and wear surface topography. Al7075+3 vol % molybdenum disulfide composite shows the lowest coefficient of friction because of its self‐lubricating nature. Al7075+3 vol % molybdenum disulfide+9 vol % zirconium diboride hybrid composite exhibits the lowest wear rate at high velocity as well as at high load and can be potentially used in manufacturing and tribological applications. Moreover, the use of this material may lead to the minimum requirement of external toxic lubricants that make it cost‐effective and environmentally sustainable. [ABSTRACT FROM AUTHOR]

This work reviews surface modification techniques for improving the wear and corrosion resistance of 42CrMo steel. The advantages and disadvantages of various methods, including thermal spraying, deposition, hardfacing, laser cladding, nitriding, and laser surface treatment, are discussed. The review elaborates on the materials commonly employed in laser cladding technology, including iron-based, cobalt-based, nickel-based, and high-entropy alloys and reinforced composite coatings. Furthermore, the mechanisms and methods of improving the wear and corrosion resistance of 42CrMo steel are summarized. Finally, this review presents research shortcomings and future opportunities of surface modification techniques. This review also provides a theoretical guide for the application of 42CrMo steel. [ABSTRACT FROM AUTHOR]

A CoCrFeNi-Ag-Mo self-lubricating composite was fabricated by spark plasma sintering. The effect of Ag and Mo addition on the microstructure, mechanical and tribological properties of CoCrFeNi high entropy alloy (HEA) was systematically investigated. Ag addition led to the formation of Ag-rich phase in CoCrFeNi HEA matrix. With the addition of Mo, part of Ag-rich phases were distributed inside the Mo-rich phase. There were clear diffusion regions between Mo and HEA matrix, residual Mo phases and dispersed Ag-rich phases in Mo-rich phases. The hardness and strength were decreased with the addition of Ag and increased with the addition of Ag and Mo. The ultimate plasticity strain of CoCrFeNi-Ag-Mo composite exceeded 45%. The coupling addition of Ag and Mo effectively improved the tribological properties from room temperature to 800 °C. This phenomenon could be ascribed to the low hardness and yield strength of CoCrFeNi-Ag composite, as well as the thermo-softening due to the friction-induced heat and high experimental temperature. At room temperature, Ag-rich phases acted as a lubricant, and Mo-rich phases improved the anti-wear property. At 400 °C, tiny Ag particles were uniformly distributed on the worn surface, which played roles in friction-reducing. At 800 °C, the Ag2MoO4 layers in-situ formed by tribo-chemistry reactions offered good lubricating and anti-wear functions. [ABSTRACT FROM AUTHOR]

Cured epoxy resins have poor abrasion resistance, which shortens the service life of the material. This work aims to improve the tribological properties of epoxy resins by coupling self‐lubrication and auto‐healing. In this study, linseed oil microcapsules with an average particle size of 38.57 μm and good thermal stability were successfully prepared by in situ polymerization. The effects of microcapsule content on the tribological, mechanical, and self‐healing properties of the composite coatings were studied. It was demonstrated that the composite coating has outstanding self‐lubricating properties. The coefficient of friction reduced from 0.634 (pure epoxy resin) to 0.0459 (epoxy resin with 10 wt.% linseed oil microcapsules). Wear rate reduced from 7.16 × 10−4 mm3/(N m) to 1.74 × 10−5 mm3/(N m). The self‐lubricating mechanism of the coating was investigated by SEM and EDS, which indicated that the formation of uniform and continuous lubricating film on the surface of the friction pairs was the key to improving the wear resistance of the material. In addition, the linseed oil released after the microcapsules rupture can repair the abrasion marks by reacting with oxygen during the friction process. The dual‐functional effect of linseed oil microcapsules prolongs the life of epoxy resin coating and expands its application range. [ABSTRACT FROM AUTHOR]

The primary objective of this research is to investigate the structure and tribological properties of NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer films in a wide temperature range (RT-1000 °C). The bilayer films were prepared by pulsed laser deposition (PLD) technology, so as to provide the theoretical basis and experimental guidance for the study of the synergistic lubricating effect of Mo and V bimetallic lubricating oxides. The NiCr–Mo–Ag–O composite target was fabricated by the hot-press sintering technique. Subsequently, a NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer film was deposited on Inconel 718 by pulsed laser deposition (PLD). The tribological properties of the film were evaluated by HRT-1000 high-temperature ball-on-disc configuration at RT-1000 °C. The obtained results reveal that the NiCr–Mo–Ag–O target is marked by a compact structure and homogeneous composition. Furthermore, the composite film exhibits a smooth surface and dense structure, comprised of polycrystalline and amorphous phases. The measured hardness and elastic modulus of the film approximated 4.9 GPa and 153.5 GPa, respectively. Additionally, the lowest friction coefficient of the film is about 0.28 at 800 °C. Upon reaching this temperature, the cooperative lubrication resulting from NiMoO4, Ag2Mo2O7, and AgVO3 contributed effectively towards reducing the film's friction coefficient.

The evolution of pearlite into an amorphous wrapped nanolamellar heterostructure (AWNH) within the tribolayer is an important process for the formation and stabilization of a nanocomposite self-lubricating surface. Here, experimental characterizations were performed to show that an AWNH was an intermediate product of transformation of pearlite to oxide nanoparticles and played a supporting role as a self-lubricating layer of the substrate. Furthermore, the molecular dynamics simulation method was used to analyze the wear properties and load-bearing capacities of four different microstructures to reveal the unique AWNH deformation mechanism and its effect on the self-lubrication behavior. The results showed that the AWNH exhibited a low friction and good wear resistance, which could be ascribed to its high hardness, high plasticity, and outstanding interface deformation coordination ability. The shear bands were restricted by the nanolamellar structure, and the shear transition zone that formed at the interfaces caused the plastic deformation to be uniformly distributed, which provided favorable conditions for supporting the self-lubricating layer. The results of this study provide theoretical guidance for analyzing the deformation mechanisms and tribological behaviors of AWNHs and help to optimize self-lubricating material design.

In recent years, there has been significant attention on the application potential of medium and high-temperature self-lubricating composites as sliding parts in extreme environments. This study examines the effects of different Mo and Ag content on the composition and wear resistance of Ni60-cladded coatings at room temperature, 300 °C and 600 °C, while also analyzing their wear mechanism by studying the tribofilm. The results indicate that with an appropriate weight addition of Mo and Ag, one typical lubricant called Ag2MoO4 emerges. At room temperature, the cladding layer containing 5 wt.% Mo and 5 wt.% Ag exhibits a wear rate of 2.08 × 10−6 mm3/Nm, and an average coefficient of friction (COF) of 0.3410. These two are 85% and 11% lower than those of the Ni60 cladding layer, respectively. At 300 °C, MoO3 and Cr2MoO6 act as solid lubricants. Furthermore, at 600 °C, a MoSi2 and SiO2 film forms on the worn surface to prevent further oxidation of MoSi2 and enhance oxidation resistance. The main wear mechanism is adhesion wear. Under higher temperatures, the newly formed Ag2MoO4 in the composite cladding layer adopts a layered cubic spinel structure where low-energy Ag-O bonds preferentially break during friction processes, demonstrating excellent lubrication performance. [ABSTRACT FROM AUTHOR]

A series of CoCrFeNiMn high-entropy alloy matrix self-lubricating composites were prepared by spark plasma sintering. The composites are composed of an FCC phase, Cr7C3, Ag, and eutectic fluoride BaF2/CaF2 phases. The microstructure of the composites is uniform. The additional phases distribute along the boundary of equiaxed grains of the FCC phase. The compressive yield strength and fracture toughness decrease with the increase of eutectic fluoride BaF2/CaF2. The composites are susceptible to brittle cleavage fracture. [ABSTRACT FROM AUTHOR]

To improve the service performance of diamond cutting tools under dry working conditions, three oxides (B2O3, TiO2, and ZnO) were innovatively used to prepare oxide self-lubricating diamond cutting-tool matrix. Rockwell hardness, three-point bending strength, and relative density tests were conducted to determine the effects of oxides on the mechanical properties of diamond cutting-tool matrix from the macroscale, whereas SEM, EDS, roughness test, physical, and molecular-dynamic-simulated dry-wear tests were used synthetically to explore the effects of oxides on the wear behavior of diamond cutting-tool matrix. Test results indicated that proper oxide addition improved the tribological properties of diamond cutting-tool matrix but decreased its mechanical properties to some degree. Furthermore, oxides more easily slid during the dry-wear process by changing its molecular-group morphologies. Consequently, self-lubricating films were generated and the wear resistance of the diamond cutting-tool matrix increased with the decrease in fatigue wear and fractured abrasive wear. [ABSTRACT FROM AUTHOR]

The self-lubricating mechanism of Cu–Pb bearing alloy is discussed by molecular dynamics (MD). MD friction tests are conducted on the pure Cu and Cu–Pb models. The Pb-rich secondary phases (PSPs) melt due to the frictional heat. The solid–liquid phase transition of Pb is characterized by the radial distribution function (RDF) and the potential energy. An obvious drop of motion resistance of the abrasive debris is observed in Cu–Pb alloy once the debris moves close to the soft PSP which protect the matrix from abrasion by embedding the debris and promoting the formation of a liquid lubricant film. The synchrotron radiation technology is employed to in-situ observe the phase transition of Pb, and the MD results match the experimental results well.

Abstract High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load, high temperature, high shock conditions due to in-sufficient supply of lubricating oil and grease. Traditional self-lubricating coatings prepared by inorganic, organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function, so that it is difficult to meet the engineering requirements of high-temperature lubrication. We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy. Polytetrafluoroethylene (PTFE, T m = 329 °C) and polyphenylene sulfide (PPS, T g = 84 °C, T m = 283 °C) are used to prepare a PTFE/PPS polymer alloy coating. As the temperature increases from 25 to 300 °C, the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state, which is owing to the thermodynamic transformation characteristic of the PPS component. Additionally the friction coefficient (µ) decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300 °C. The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature (T), temperature-centrifugal force (T-F ω ), temperature-centrifugal force-shearing force (T-F ω -F τ ) were investigated. The physical model of “thermoviscoelasticity driven solid-liquid interface reducing friction” is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers. The high-temperature adjusts the viscosity (η) of the coating, increases interface slipping and intensifies shear deformation (τ), reducing the friction coefficient. The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.