Journal of Friction and Wear最新文献

In the present work, the mechanical properties and tribological characteristics of TiN (monolayer) and TiN/a‑C (bilayer; two variants of combinations of elastoplastic properties of the layers) coatings were investigated using experimental and theoretical approaches. The microstructure of the synthesized coatings and the topography of the surface were characterized by scanning electron microscopy. Characterization of the a‑C coating was carried out by the diffuse total internal reflection (DTIR) method using a Fourier‑transform infrared (FT‑IR) spectrometer. Hardness and reduced modulus were obtained by continuous (instrumented) indentation with a Berkovich indenter. Wear rate and coefficient of friction were determined in sliding friction tests. The results of the comprehensive experimental study of the coatings served as the basis for developing a finite‑element model of indentation of a bilayer elastoplastic medium with various combinations of elastic and plastic properties and different relative layer thicknesses. A correlation between coating parameters H/E and H³/E² and the wear rate was established experimentally. Functional dependences of hardness and reduced modulus on the relative thickness of the surface metastable a‑C layer were determined theoretically. The optimal ratio of the thicknesses of the constituent layers in the TiN/a‑C coating for given elastoplastic material properties, yielding the best tribological performance, was identified.

The paper studies the microstructure, phase composition, mechanical properties, and tribological characteristics of copper matrix composites of the Cu–Fe–FeCr–MoS₂–C system reinforced with TiC–Ti composite inclusions sized 100–140 and 140–200 μm. The composites under study were obtained by sintering under pressure, and the content of reinforcing TiC–Ti inclusions was 3, 5, 7, 9, and 11 vol %. It is shown that the hardness of the composites under study increases with the addition of TiC–Ti metal-ceramic inclusions to 15 HBW 10/250/30, which is more than 40% higher than the hardness of the matrix composite. It is revealed that composites reinforced with TiC–Ti inclusions have greater wear resistance compared to the matrix composite without the introduction of reinforcing inclusions. It was found that the composite containing 7 vol % TiC–Ti inclusions 100–140 μm in size has the highest wear resistance, and an increase in the inclusion content to 9 and 11 vol % leads to an increase in the wear intensity of the composite. With the introduction of more than 7 vol % TiC–Ti composite inclusions 140–200 μm in size, a decrease in wear resistance also occurs. The maximum friction coefficient is demonstrated by the composite reinforced with 11 vol % TiC–Ti inclusions 100–140 μm in size, which is 0.36 ± 0.03, and with an increase in the inclusion size to 140–200 μm, the highest friction coefficient is observed with the introduction of 7 vol % TiC–Ti.

Reduction of the metal consumption of tools used for extraction of solid minerals is directly related to their wear resistance. This study investigated the material selection requirements for excavator bucket teeth based on scientific data. The aim of the work was to determine the optimal chemical composition and final heat treatment to provide the required combination of mechanical properties for excavator bucket teeth to be used under various operating conditions. Experimental steel specimens were produced in induction furnaces with a capacity of up to 120 kg. Heat treatment was carried out by quenching in oil followed by either low or high tempering. Wear tests used a friction scheme in which a specimen mounted in the machine spindle undergoes transverse motion while simultaneously rotating about its axis. The highest strength values were obtained for the steel with 0.4% C (ultimate tensile strength 1720 MPa) compared with 0.3% C (1680 MPa) at the same level of plastic properties. Analysis of the wear-test results showed the most severe wear conditions when using SiC abrasive with a particle size of 200 µm (66–71 m/g; 82–89 m/g). High hardness after quenching and low tempering guarantees better wear resistance (130–133 m/g) compared with quenching and high tempering (95–110 m/g). The primary wear mechanisms are micro-cutting and plastic ploughing (plastic displacement). Taking the results and the application conditions of excavator buckets in the extraction of various rock types into account, the following steels are recommended for bucket teeth: 30KhGNMFL for conditions requiring high wear resistance and low-temperature toughness; 40Kh2GN2MFL (No. 3) for more temperate climates. Low tempering after quenching is recommended for temperate climates; to ensure low-temperature toughness, quenching followed by high tempering is necessary.

The effect of gamma irradiation on some physicomechanical and tribological properties of VK-8 cemented carbide was investigated. Samples were CNMG 120408-46 indexable cutting inserts (manufacturer Sandvik MKTS, Russia) intended for turning. They were subject to gamma irradiation at various doses from 20 to 200 kGy and in different gaseous environments (air and nitrogen). Irradiation was carried out on an industrial GUD-300M facility using ⁶⁰Co sources. Tests showed that after irradiation, a decrease in the electrical resistivity of the samples was observed, confirming the hypothesis of microstructure ordering in the irradiated material. Hardness measurements before and after irradiation did not reveal significant changes. However, a significant increase in the wear resistance of the material during cutting of various steels was established, from 1.5 to 6 times, depending on the absorbed irradiation dose, the steel being machined, and the cutting parameters. It is suggested that there exists an “optimal” level of gamma irradiation, below and above which the effect of radiation modification decreases. Determining this level requires separate tests for each material studied. However, general trends of increased wear resistance have been established in this article.

The need to use solid lubricating coatings (SLCs) arose with the launch of the first space satellites, in which cold welding of articulated joints took place. SLCs have the following main advantages [1, 2, 4]: low evaporation in a vacuum, low friction coefficient, and performance in zero gravity. They can be used in outer space conditions over a wider temperature range than frost-resistant plastic lubricants. The selection of the most suitable SLC [3–6] requires a thorough study of their tribotechnical characteristics depending on the design of friction units, frictional interaction parameters, and environmental characteristics. SLCs are capable of operating in a wide range of temperatures in air, vacuum, and gas environments; they have a radiation resistance of 10⁶–10¹⁰ rad depending on the binder; they are capable of withstanding high contact loads and are insensitive to zero gravity. The most widespread SLCs are in the form of suspensions of solid lubricant with a binder, applied by a spray gun with subsequent curing by heat treatment. A wide range of coatings has been developed: VNIINP-213, VNIINP-512, VNIINP-513, APF-5, EONIT-3, and Dimolits. We conducted tribological testing of the above coatings using various friction pair configurations, in air and vacuum, at various temperatures, and across a wide range of loads and sliding speeds. These data are important for selecting coatings for friction components being developed for spacecraft.

Comparative physical, mechanical, and tribotechnical studies of the effect of various C₆₀ fullerene contents in polymethylmethacrylate (PMMA) polymer films on sliding friction have been carried out during finger–disc testing. It is shown that an increase in the concentration of the fullerene modifier to 1% leads to a decrease in surface roughness at the nanoscale and the coefficient of friction of PMMA paired with aluminum alloy D16. As the concentration of C₆₀ fullerenes in polymer films increases to 3%, they coagulate and form inhomogeneously distributed nano-concentrators with a diameter of about 150 nm. At the same time, the tribological properties of polymer films deteriorate. The coefficient of friction of PMMA paired with D16 aluminum alloy increases compared to the initial state. With an increase in the content of C₆₀ fullerene in polymer films, their density and microhardness increase, and the burgundy color appears and unambiguously increases. When PMMA was rubbed in its initial state (without the addition of C₆₀) in combination with aluminum alloy D16, adhesive processes were detected, and as a result, aluminum was transferred to the polymer film with an increase in the coefficient of friction. The studied films turned out to be heterogeneous in composition and properties, subject to warping, with insufficient dispersion of the material at the nanoscale.

It is shown that during drilling, cleaning of drilling solution using centrifugal decanters minimizes the presence of abrasive particles in the system and reduces mechanical wear of structural elements and pumping units. The results of a comparative analysis of the resource of the initial nozzle design and three proposed modifications, differing in surface geometry and orientation relative to the direction of rotation of the drum, are presented. A comprehensive assessment of the effect of design changes on the particle escape velocity and, as a result, on the wear rate was carried out using an analytical model for calculating the amount of wear during particle impact. A discrete-element model of the processes accompanying the operation of a centrifugal decanter (movement of drilling solution along the centrifuge screw) has been developed. The time before the formation of critical wear (destruction) of the nozzle surfaces is calculated. The influence of geometric and design parameters of centrifugal decanter nozzles on the efficiency of the drilling solution cleaning process has been studied. It is shown that reducing the height and diameter of the nozzles to 34 and 37 mm, respectively, increased the surface wear time by 1.5 times. An analytical evaluation of the resource of cylindrical nozzle surfaces for various design options has been performed. A significant increase in service life is achieved by changing the inclination of the cylindrical surfaces of the nozzles against the direction of rotation of the drum. The wear time of the nozzle surface increases 12.5 times.

Methods of X-ray diffraction, X-ray phase analysis, and optical metallographic microscopy were used to study the mechanisms of influence of lubricating compositions based on a dispersion medium, tetraether pentaerythritol C₅–C₉ (TEPE C₅–C₉), with soap dispersed phases on the structure and physicomechanical characteristics of the surface layers of CuAl5 bronze after its friction in a pair with C45 steel. Concentrated surface-active substances (surfactants) were used as dispersed phases (thickeners): lithium soap of 12-hydroxystearic acid (12-LioSt), calcium soap of 12-hydroxystearic acid (12-CaoSt), as well as complex calcium soap, including a composition of salts of 12-hydroxystearic and acetic acids (k-Ca). It has been shown that after friction of bronze, an alternative change in the yield strength of the surface layer of the samples (Rehbinder and Roscoe effects) occurs in all lubricating compositions, depending on the composition. The appearance of internal residual mesostresses in this layer as a result of tribodeformation triggers an ascending diffusion mechanism, causing a concentration redistribution of the components in the material, up to the complete removal of the alloying element atoms from its near-surface layer (selective transfer mode). It is shown that changes in the mechanical properties of the material and its wear resistance depend on the colloidal-chemical parameters of the surface and oxidative activity of the lubricant composition, determined by the hydrophilic-lipophilic balance of the molecules of its components. Thus, the introduction of 12-LioSt additive into the base medium of TEPE C₅–C₉ reduces the wear rate of bronze by 1.3 times, the addition of k-Ca additive, by 6.5 times, and the introduction of 12-CaoSt additive increases this rate by 10%.

This article demonstrates the relationship between a decrease in energy efficiency and the load-carrying capacity of worm gears with an increase in the amplitude of torque oscillations as the coupling load increases. An analysis is conducted of the causes of the increase in the amplitude of torque oscillations with increasing gear load. It is shown that the disruption of the self-oscillation mode occurring in a worm gear should occur due to an increase in the friction coefficient, which depends on the lubrication conditions, in particular, on the thickness of the lubricant film. The study demonstrates that in the case of lubrication of the gear with standard mineral oil with a nano-modified additive, the loss of stability of self-oscillations occurs at significantly higher loads (290 N m) than in the case of lubrication with standard mineral oil without the additive (230 N m), indicating greater resistance of this option to disturbing effects and can be explained by the greater thickness of the lubricant film. The study obtained graphs of the dependence of the worm gear efficiency on the braking torque for various lubricant options. It is shown that the increase in efficiency when using standard mineral oil with a nanomodified additive (a nanodispersed suspension of serpentine in a solution of fatty acid salts) compared to standard mineral oil is associated with improved antifriction properties of the coupling and a reduction in the amplitude of torque oscillations. The study demonstrates that the stability of a worm gear under load can be experimentally assessed by measuring the amplitude of torque oscillations on the high-speed shaft of the gear. To expand the range of permissible loads, it is necessary to improve the antifriction properties of the lubricant by using a nanomodified additive. This leads to a reduction in the amplitude of self-oscillations of the worm shaft, a reduction in friction path, and a reduction in power losses.

The study presents the results of an investigation into the tribological properties of hardening discrete coatings in vacuum, as well as composite coatings based on them with the addition of a solid lubricant layer. The subject of the research is discrete coatings based on thin TiBN films, formed by magnetron sputtering of material through photoresist masks of various geometric configurations, using explosive photolithography technology. Composite coatings were produced by magnetron deposition of a solid lubricant MoS₂ layer onto the discrete TiBN coating. The study evaluates the influence of the discrete structure geometric parameters (characteristic size of discrete elements, coating continuity, and thickness) on wear resistance and the coefficient of friction. It also examines the failure mechanisms of the investigated coatings under high contact loads in vacuum conditions. Steel plates made from 12Сr18Ni10Ti (AISI 321 equivalent) were used as substrates. The wear-resistant TiBN coatings were deposited by magnetron sputtering of a TiB target in an argon and nitrogen environment. The solid lubricant coatings were deposited by magnetron sputtering of a stoichiometric MoS₂ target in an argon environment. Tribometric tests of the coated samples were carried out using a high-vacuum tribometer equipment in a “sphere-on-flat” configuration, employing a strain gauge measurement system. Scanning electron microscopy was used to analyze the morphological features of wear tracks. Discrete TiBN coatings with characteristic element sizes ranging from 460 to 805 μm and continuity values from 0.25 to 0.7 were used in the study; the coating thickness varied from 0.88 to 2.11 μm. The results demonstrate a significant influence of the discrete structure parameters on the tribological performance. Samples with discrete elements of 700 μm in diameter, 1 μm in thickness, and 0.6 continuity showed the best wear resistance and the most stable coefficient of friction. Incorporating a solid lubricant MoS₂ layer into the discrete coating significantly reduced the coefficient of friction to the range of 0.03–0.07 and improved frictional stability during prolonged operation in vacuum. These findings confirm the promising potential of using discrete hardening coatings combined with solid lubricant layers for tribological units operating in extreme conditions. The proposed approach can be applied to extend the service life of components in vacuum and space equipment.