The special mechanical properties of nanoparticles allow for novel applications in many fields, e.g., surface engineering, tribology and nanomanufacturing/nanofabrication. In this review, the basic ...physics of the relevant interfacial forces to nanoparticles and the main measuring techniques are briefly introduced first. Then, the theories and important results of the mechanical properties between nanoparticles or the nanoparticles acting on a surface, e.g., hardness, elastic modulus, adhesion and friction, as well as movement laws are surveyed. Afterwards, several of the main applications of nanoparticles as a result of their special mechanical properties, including lubricant additives, nanoparticles in nanomanufacturing and nanoparticle reinforced composite coating, are introduced. A brief summary and the future outlook are also given in the final part.
In modern electric equipment, especially electric vehicles, inverter control systems can lead to complex shaft voltages and bearing currents. Within an electric motor, many parts have electrical ...failure problems, and among which bearings are the most sensitive and vulnerable components. In recent years, electrical failures in bearing have been frequently reported in electric vehicles, and the electrical failure of bearings has become a key issue that restricts the lifetime of all-electric motor-based power systems in a broader sense. The purpose of this review is to provide a comprehensive overview of the bearing premature failure in the mechanical systems exposed in an electrical environment represented by electric vehicles. The electrical environments in which bearing works including the different components and the origins of the shaft voltages and bearing currents, as well as the typical modes of electrical bearing failure including various topographical damages and lubrication failures, have been discussed. The fundamental influence mechanisms of voltage/current on the friction/lubrication properties have been summarized and analyzed, and corresponding countermeasures have been proposed. Finally, a brief introduction to the key technical flaws in the current researches will be made and the future outlook of frontier directions will be discussed.
The nano-lubricant can largely enhance the tribological property of base oil, while the higher addition will cause a serious aggregation of nanoparticles. In this paper, the hexadecane-based oil ...(16C) with ultralow concentration of graphene oxide (GO) nanosheets as lubricant additives were successfully prepared by phase transfer method. The tribological behavior of the hexadecane with different concentration of GO has been investigated by subjecting it to macroscopic ball-on-disc friction tests using SRV-4 tribometer. The steady-state coefficients of friction (COF) of 16C with 10 mg/L GO were ca. 0.146. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism was proposed. It is believed that the adsorption of GO nanosheets on the lubricated surfaces of both the ball and disk is the key to reduce friction and wear. The proper addition of GO nanosheets can easily enter into the contact area and efficiently protect the surface of the sample from wear.
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•The based oil with ultralow concentration of graphene oxide nanosheets were prepared by phase transfer method.•Cooperative antifriction mechanism of low intermolecular shear of oleylamine and low interlaminar shear of GO sheets are proposed.•The nanosheets of graphene oxide adsorbed on the counterpart surface exert a protective effect against wear.•The lower addition of GO nanosheets can easily enter into the contact area.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Owing to the diverse composition, adjustable performance, and synergistic effect among components, core–shell micro/nanoparticles have been widely applied in the field of tribology in recent years. ...The strong combination with the matrix and the good dispersion of reinforcing fillers in the composites could be achieved through the design of core–shell structural particles based on the reinforcing fillers. In addition, the performance of chemical mechanical polishing could be improved by optimizing the shell material coated on the abrasive surface. The physical and chemical state of the core–shell micro/nanoparticles played important effects on the friction and wear properties of materials. In this paper, the synthesis methods, the tribological applications (acted as solid/liquid lubricant additive, chemical mechanical polishing abrasives and basic units of lubricant matrix), and the functionary mechanisms of core–shell micro/nanoparticles were systematically reviewed, and the future development of core–shell micro/nanoparticles in tribology was also prospected.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In recent years, a new 2D-layered material—black phosphorus (BP)—has been a rising star after the era of graphene owing to its high charge carrier mobility, tunable direct bandgap and unique in-plane ...anisotropic structure. With the development of the synthesis and modification methods of BP, its extensive applications, e.g., transistors, batteries and optoelectronics have emerged. In order to explore its full potential, research into the tribological properties of BP 2D-layered materials such as lubrication additives and fillers in self-lubricating composite materials would be not only of high scientific value but also of practical significance. In this work, recent advances on the friction and lubrication properties of BP nanosheets made by our group, including the micro-friction properties, the lubrication properties of BP nanosheets as water-based and oil-based lubrication additives, and the friction and wear of BP/PVDF composites will be presented. Finally, the future challenges and opportunities in the use of BP materials as lubricants will be discussed.
Self-lubricating polymer composite coatings, with tailorable tribological and mechanical properties, have been widely employed on mechanical parts to reduce friction and wear, which saves energy and ...improves the overall performance for applications such as aerospace satellite parts, shafts, gears, and bushings. The addition of functional fillers can overcome the limitations of single-polymer coatings and extend the service life of the coatings by providing a combination of low friction, high wear resistance, high load bearing, high temperature resistance, and high adhesion. This paper compares the heat resistance, and the tribological and mechanical properties of common polymer matrices, as well as the categories of functional fillers that improve the coating performance. Applicable scopes, process parameters, advantages, and limitations of the preparation methods of polymer coatings are discussed in detail. The tribological properties of the composite coatings with different matrices and fillers are compared, and the lubrication mechanisms are analyzed. Fillers reduce friction by promoting the formation of transfer films or liquid shear films. Improvement of the mechanical properties of the composite coatings with fillers of different morphologies is described in terms of strengthening and toughening mechanisms, including a stress transfer mechanism, shear yielding, crack bridging, and interfacial debonding. The test and enhancement methods for the adhesion properties between the coating and substrate are discussed. The coating adhesion can be enhanced through mechanical treatment, chemical treatment, and energy treatment of the substrate. Finally, we propose the design strategies for high-performance polymer composite coating systems adapted to specific operating conditions, and the limitations of current polymer composite coating research are identified.
In recent years, attempts to improve the mechanical properties of composites have increased remarkably owing to the inadequate utilization of matrices in demanding technological systems where ...efficiency, durability, and environmental compatibility are the key requirements. The search for novel materials that can potentially have enhanced mechanical properties continues. Recent studies have demonstrated that two-dimensional (2D) nanomaterials can act as excellent reinforcements because they possess high modulus of elasticity, high strength, and ultralow friction. By incorporating 2D nanomaterials in a composite, 2D nanomaterial-based composites (2DNBCs) have been developed. In view of this, a critical review of recent mechanical and tribological studies based on 2DNBCs has been undertaken. Matrices such as polymers, ceramics, and metals, as well as most of the representative 2D nanomaterial reinforcements such as graphene, boron nitride (BN), molybdenum disulfide (MoS2), and transition metal carbides and nitrides (MXenes) have been included in this review. Their preparation strategies, intrinsic mechanical properties, friction and lubrication performances, strengthening mechanisms, influencing factors, and potential applications have been comprehensively discussed. A brief summary and prospects are given in the final part, which would be useful in designing and fabricating advanced 2D nanocomposites in the future.
Abstract
Superlubricity has recently raised an increasing interest owing to its great potential in energy saving and environmental benefits. Yet how to obtain stable superlubricity under an ultrahigh ...contact pressure (>1 GPa) still remains a challenge. Here, we demonstrate that robust liquid superlubricity can be realized even under a contact pressure of 1193 MPa by lubrication with partially oxidized black phosphorus (oBP) nanosheets. The analysis indicates that the oBP nanosheets that absorb large amounts of water molecules are retained at the friction interface and transform the friction pairs interface to that between the oBP nanosheets. Molecular dynamics simulation demonstrates that water molecules could be retained at the friction interface even under the ultrahigh contact pressure owing to the abundant P=O and P–OH bonds formed on the oBP nanosheet surfaces, contributing to the achievement of stable superlubricity under the ultrahigh contact pressure. This work has the potential of introducing the liquid superlubricity concept in diverse industrial applications involving high-contact-pressure operating conditions.
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•Effects of iron powder types and contents on the friction and wear properties of copper matrix composites for breaking of high-speed trains were investigated through microstructure ...observations and components analysis of tribofilm.•The wettability and combination between ferrophosphorus and matrix is poor and carbonyl iron is more suitable for strengthening matrix. The friction coefficient is most stable and the wear rate is also relatively low with 10% carbonyl iron.•The increase of carbonyl iron content can promote the formation of the friction film and improve the thickness, hardness and strength of the film. When the Fe content is larger than 10%, it accelerates the generation of the friction film. However, cracks are easy to form between the thicker film and softening matrix, which leads to large wear and fluctuating friction coefficient.•The oxide process during the braking is carried out from the surface to the matrix. The oxide degree of friction film increases in the direction from the matrix to the surface.
This paper studied the effects of iron powder types and contents on the friction and wear properties of copper matrix composites for breaking of high-speed trains. The mechanical properties, microstructure, interface, tribofilm, elements and microhardness of samples were analyzed by hardness tester, SEM, EDS and nanoindentation tests. The braking performances were measured by a tribometer mimicking the braking conditions. The results show that the wettability and combination between ferrophosphorus and matrix is poor and carbonyl iron is more suitable for strengthening matrix. The friction coefficient is most stable and the wear rate is also relatively low with 10% carbonyl iron. The increase of carbonyl iron content will promote oxidation and be conducive to the formation of friction film. The oxide degree of friction film increases in the direction from the matrix to the surface. However, too much iron powder produces excessive iron oxide which makes the friction film be easy to peel off especially under high speeds.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The nano-friction between MoS2 nano-sheets and AFM probes can be regulated by an external normal electric field.•Friction force will increase with the increase of the external bias.•When a threshold ...voltage is exceeded, accelerated oxidation of MoS2 will be promoted.•The tuning value of the friction force can be increased by 2 times.•A feasible and valuable strategy to adjust the friction characteristics of the MoS2 system is provided.
The friction and wear behavior of micro-molybdenum disulfide (MoS2) is studied by atomic force microscope (AFM), and both positive and negative bias are applied to the conductive probe and substrate. The experimental results show that the nano-friction between MoS2 nano-sheets and AFM probes can be regulated by an external normal electric field. Friction force will increase with the increase of the external bias. The maximum bias has a threshold value. If the bias exceeds the threshold, it will promote the formation of MoS2 charge transfer and accelerate oxidation during the friction process. The tuning value of the friction force can be increased by 2 times, compared with the friction force under the condition of non-bias. We propose a feasible and valuable strategy to adjust the friction characteristics of the MoS2 system, which provides great significance to understand and control the nano-friction in the practical application.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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