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Purpose: This study aims to investigate the effect of steel fibers on the mechanical and tribological properties of FeS/Cu–Bi self-lubricating materials. Design/methodology/approach: The microstructure of the material was characterized by scanning electron microscopy. Tests on the crushing strength, impact toughness and tribological properties of materials were conducted using a universal electronic testing machine, a 300 J pendulum impact testing machine and an M200 ring-block sliding tribometer, respectively. Findings: The mechanical properties of the material initially increased and then stabilized with increased copper-plated steel-fiber length. When the length of the copper-plated steel fiber was 7 mm, the mechanical properties of the material reached stability. Compared with the material without a copper-plated steel fiber, its crushing strength and impact toughness increased by 32.6% and 53%, respectively. A copper-plated steel fiber with a length of 7 mm lay flat in a copper matrix can strengthen the friction interface and enrich the lubricant. Accordingly, the antifriction and wear resistance of the materials increased by 17.6% and 55%, respectively. Originality/value: The effects of copper-plated steel fibers on the properties of FeS/Cu–Bi self-lubricating materials were clarified. This work can serve as a reference for improving material performance and its engineering applications. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the effect of chemical nickel plating and mechanical alloying on the mechanical and tribological properties of FeS/iron-based self-lubricating materials as well as the wear mechanism of the materials. Design/methodology/approach: Surface modification of FeS powder was carried out by chemical nickel plating method and mechanical alloying of mixed powder by ball milling. The mechanical properties of the material were tested by tribological testing by M-200 ring block type friction and wear tester. Optical microscope was used to observe the surface morphology of the material and the transfer film on the surface of the mate parts, and scanning electron microscope and EDS were used to characterize the wear surface. Findings: Mechanical alloying ball milling was carried out so that the lubricating particles in the matrix are uniformly dispersed; nickel-plated layer enhances the interfacial bonding of FeS and the matrix, and the combination of the two improves the mechanical properties of the material, and at the same time the friction side of the surface of the lubrication of FeS lubricant transfer film formed is denser and more intact, and the friction coefficient of friction side and the wear rate of the material have been greatly reduced. Originality/value: This work aims to improve the mechanical and tribological properties of FeS/iron-based self-lubricating materials and to provide a reference for the preparation of materials with excellent overall properties. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the effects of ball–material ratio on the properties of mixed powders and Cu-Bi self-lubricating alloy materials. Design/methodology/approach: Cu-Bi mixed powder was ball milled at different ball–material ratios, and the preparation of Cu-Bi alloy materials was achieved through powder metallurgy technology. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were conducted to study the microstructure and phase composition of the mixed powder. The apparent density and flow characteristics of mixed powders were investigated using a Hall flowmeter. Tests on the crushing strength, impact toughness and tribological properties of self-lubricating alloy materials were conducted using a universal electronic testing machine, 300 J pendulum impact testing machine and M200 ring-block tribometer, respectively. Findings: With the increase in ball–material ratio, the spherical copper matrix particles in the mixed powder became lamellar, the mechanical properties of the material gradually reduced, the friction coefficient of the material first decreased and then stabilized and the wear rate decreased initially and then increased. The increase in the ball–material ratio resulted in the fine network distribution of the Bi phase in the copper alloy matrix, which benefitted its enrichment on the worn surface for the formation a lubricating film and improvement of the material's tribological performance. However, a large ball–material ratio can excessively weaken the mechanical properties of the material and reduce its wear resistance. Originality/value: The effects of ball–material ratio on Cu-Bi mixed powder and material properties were clarified. This work provides a reference for the mechanical alloying process and its engineering applications. [ABSTRACT FROM AUTHOR]

Purpose: Gears are prone to instantaneous failure when operating under extreme conditions, affecting the machinery's service life. With numerous types of gear meshing and complex operating conditions, this study focuses on the gear–rack mechanism. This study aims to analyze the effects and optimization of biomimetic texture parameters on the line contact tribological behavior of gear–rack mechanisms under starvation lubrication conditions. Design/methodology/approach: Inspired by the microstructure of shark skin surface, a diamond-shaped biomimetic texture was designed to improve the tribological performance of gear–rack mechanism under starved lubrication conditions. The line contact meshing process of gear–rack mechanisms under lubrication-deficient conditions was simulated by using a block-on-ring test. Using the response surface method, this paper analyzed the effects of bionic texture parameters (width, depth and spacing) on the tribological performance (friction coefficient and wear amount) of tested samples under line contact and starved lubrication conditions. Findings: The experimental results show an optimal proportional relationship between the texture parameters, which made the tribological performance of the tested samples the best. The texture parameters were optimized by using the main objective function method, and the preferred combination of parameters was a width of 69 µm, depth of 24 µm and spacing of 1,162 µm. Originality/value: The research results have practical guiding significance for designing line contact motion pairs surface texture and provide a theoretical basis for optimizing line contact motion pairs tribological performance under extreme working conditions. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate how ball milling (BM) and load influence transfer film on counterbody and the correlation between transfer film and tribological properties of copper-based composites. Design/methodology/approach: The copper-based mixed powders preprocessed by BM for different times were used to manufacture sintered materials. Specimens were tested by a custom pin-on-flat linear reciprocating tribometer and characterized prior and after tests by optical microscope, scanning electron microscope and energy-dispersive spectroscopy. Image J® and Taylor-hobson-6 surface roughness meter were used to quantify the coverage and thickness of the transfer film. Findings: Main results show that an appropriate amount of BM time and applied load can contribute to the formation of the transfer film on counterbody and effectively improve the tribological properties of the copper-based material. The transfer film coverage is linearly related to the friction coefficient, thickness of transfer film and wear volume. As the transfer film coverage increases, the coefficient of friction decreases. As the thickness of the transfer film increases, the amount of wear increases. Originality/value: This work intends to control and optimize the formation of transfer film, thereby helping improve the tribological properties of materials and providing a reference to guide the preparation of Cu-based composites with excellent tribological properties. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to put forward the lubrication model of oil bearing and enrich the design theory under the condition of mixed lubrication. Design/methodology/approach: A mixed lubrication model of bilayer porous bearing is established. The effects of the working conditions on the lubrication performance and seepage behavior were analyzed. Findings: Results show that the oil film pressure mainly occurs in the bearing convergence zone and contact pressure mainly occurs near the minimum film thickness. The oil infiltrates into the porous matrix in the contact area and precipitates out to the friction surface at the inlet of the contact area. The oil seepage velocity and dynamic pressure effect at the friction interface can be improved by reasonably matching the load and speed. With the decrease of the external load or increase of the rotating speed, the lubrication performance becomes well. Originality/value: This study provides a reference for the design and application of oil bearing under harsh working conditions. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the effect of MoS2 powder on tribological properties of sliding interfaces. Design/methodology/approach: Loose MoS2 powder was introduced in the gap of point-contact friction pairs, and sliding friction test was conducted using a testing machine. Friction noise, wear mark appearance, microstructure and wear debris were characterized with a noise tester, white-light interferometer, scanning electron microscope and ferrograph, respectively. Numerical simulation was also performed to analyze the influence of MoS2 powder on tribological properties of the sliding interface. Findings: MoS2 powder remarkably improved the lubrication performance of the sliding interface, whose friction coefficient and wear rate were reduced by one-fifth of the interface values without powder. The addition of MoS2 powder also reduced stress, plastic deformation and friction temperature in the wear mark. The sliding interface with MoS2 powder demonstrated lower friction noise and roughness compared with the interface without powder lubrication. The adherence of MoS2 powder onto the friction interface formed a friction film, which induced the wear mechanism of the sliding interface to change from serious cutting and adhesive wear to delamination and slight cutting wear under the action of normal and shear forces. Originality/value: Tribological characteristics of the interface with MoS2 powder lubrication were clarified. This work provides a theoretical basis for solid-powder lubrication and reference for its application in engineering. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0150/ [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper was to study the hydrodynamic lubrication of rough bilayer porous bearing to reveal the effect of percolation. Design/methodology/approach: The seepage lubrication model of the circular bilayer porous bearing was established in polar coordinates. The digital filtering technique and Darcy's law were used to simulate the rough surface and the percolation characteristic of the oil bearing, respectively. The influence of the structural parameters on the lubrication performance was analyzed. Findings: Compared with the ordinary monolayer oil bearing with high porosity, the bilayer bearing can reduce the whole porosity, prevent oil infiltrating into the porous medium and have better lubrication performance. The lubrication performance of bilayer oil bearing is better than that of the single-layer oil bearing which has a higher porosity. With increasing root-mean-square roughness or decreasing surface porosity, the lubrication performance of the bilayer bearing improves. The lower the porosity of the surface layer, the better the lubrication performance. Originality/value: This research provides a theoretical basis for clarifying the lubrication mechanism and influence the mechanism of the bilayer oil bearing. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to fabricate a FeS/Cu-Bi copper-based lead-free bearing material to maintain good friction-reducing and anti-adhesive properties under boundary lubrication conditions. Design/methodology/approach: The materials were fabricated by mechanical alloying and powder metallurgy and tested under dry friction conditions using HDM-20 wear tester. Findings: The results show that mechanical alloying can improve the antifriction and wear resistance of the materials. The 6 per cent FeS and 6 per cent Bi in the copper-based bearing materials fabricated by mechanical alloying have a better synergism which contributes to the friction and wear properties of copper matrix. Originality/value: This new approach solves the problems of Bi and FeS mutual segmentation, mutual agglomeration and poor interface bonding. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to obtain high mechanical and good tribological properties of epoxy resin-based coatings under dry friction conditions.Design/methodology/approach Bonded solid lubricant coatings containing Kevlar fibres were prepared by a spraying method. The friction and wear properties of the coatings were experimentally investigated with a face-to-face tribometre under dry friction conditions. Scanning electron microscopy, energy dispersive X-ray spectroscopy and 3D laser scanning technologies were used to characterise the tribological properties. The action mechanism of the Kevlar fibres on a solid lubricant transfer film was also analysed.Findings Adding Kevlar fibres can significantly improve the wear resistance of the coatings. When the Kevlar fibre content increases, the tribological properties of the coatings improve and then worsen. Superior properties are obtained with 0.03 g of Kevlar fibres. Appropriately increasing the load or speed is beneficial to the removal of the outer epoxy resin and the formation of a lubricant film. During friction, the solid lubricants wrapped in the epoxy resin accumulate on the surface to form a transfer film that shows a good self-lubricating performance. In the later friction stage, fatigue cracks occur on the solid lubricant film but cannot connect to one another because of the high wear resistance and the entanglement of the rod-like Kevlar fibres. Thus, no large-area film falls from the matrix, thereby ensuring the long-term functioning of solid lubricant coatings.Originality/value Epoxy resin-based solid lubricant coatings modified by Kevlar fibres were prepared, and their friction and wear properties were investigated. Their tribological mechanisms were also proposed. This work provided a basis for the analysis of the tribological properties and design of bonded solid lubricant coatings containing Kevlar fibres. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to obtain high mechanical strength and good self-lubricating property of iron-based powder metallurgy materials. A new type of bilayer material with dense substrate and porous surface was proposed in this paper to obtain high strength and good self-lubricating property.Design/methodology/approach The materials were prepared by powder metallurgy. Their friction and wear properties were investigated with an end-face tribo-tester. Energy dispersive spectrometer, X-ray diffraction and the 3D laser scanning technologies were used to characterise the tribological properties of materials. The tribological and bearing mechanisms of the monolayer and bilayer materials were compared.Findings The results show that adding proper TiH2 can effectively improve the porosity and hardness. With the TiH2 content increased from 0 to 4 per cent, the average friction coefficients increase slowly, and the wearability decreases first and then increases. When containing 3.5 per cent TiH2, high strength and good self-lubrication characteristics are obtained. Besides, the tribological properties of monolayer materials are better than those of bilayer materials when the load is between 980 and 1,470 N, while the opposite result is obtained under the load varied from 1,470 to 2,450 N. In the bilayer material, the porous oil surface can lubricate well and the dense substrate can improve the mechanical property. So, its comprehensive tribological and mechanical properties are better than those of monolayer material.Originality/value The friction and wear properties of a new type bilayer materials were investigated. And their tribological mechanisms were proposed. This work can provide a theoretical reference for developing high-performance iron-based oil materials under boundary lubrication. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to discuss the combined effects of the deterministic surface roughness and porous structure on the lubrication property of the multi-layer bearing.Design/methodology/approach Digital filtering technique and Kozeny-Carman equation are used to simulate the random Gauss surface and the internal pore structure of the porous bearing, respectively. Effects of surface morphology, structure and pores on the lubrication property are discussed by using the finite difference method.Findings Results show that the lubrication performance of the multi-layer bearing increased with the increase of the surface roughness. Also, the transverse surface is better than that of the longitudinal surface. Moreover, lubricating property is getting worse with the increase of the height of each layer and the porosity. The lower permeability surface is beneficial to improve the lubrication performance when the total porosity is certain.Originality/value The effect of the Gauss roughness parameters on the detail of lubrication performance are analysed, such as the migration of the oil film rupture point position, the expansion of the pressure distribution region and the fluctuation of the pressure distribution curve with the roughness parameters. The combined effects of surface roughness, multi-layer structure and the internal pore parameters on the hydrodynamic behaviours of multi-layer porous bearing are analysed. This work is beneficial for the analysis of the tribological property and the structural design of multi-layer bearing. [ABSTRACT FROM AUTHOR]