A multicriteria approach to the comprehensive analysis of the tribotechical characteristics and physical and mechanical properties of vegetable oils has been suggested for their comparison and selection as a lubricant base. Edible oils—refined rapeseed (RR), unrefined linseed (LO), and refined sunflower (RS)—were studied as well as industrial oils—rapeseed (RT) and castor (CT). Their fatty acid composition, viscosity index, flash and pour points, oxidative stability, friction coefficient, wear index, critical load, and welding load were analyzed. The objects of analysis were represented as points in the multidimensional space of their normalized physical and mechanical properties and tribotechical characteristics. An integrated criterion for comparison of oils as a measure of distance to a hypothetically inferior sample has been suggested. This allowed the oils to be ranked by suitability as a lubricant base (from best to worst): RT, LO, CT, RR, and SO. The position of oils in the principal component space was determined, and the directions and magnitudes of load vectors on the oil characteristics were established. A correlation between the physical and mechanical properties and tribotechical characteristics was revealed, which allowed these indicators to be related to the characteristics of the oils’ fatty acid composition. Based on the analysis of oil positions in the principal component space, the conclusion on the potential for developing a composition of RT, CT, and LO oils with a possible synergistic effect for improving load-carrying capacity, oxidative stability, and viscosity-temperature properties has been drawn. The results obtained can be used to develop effective biodegradable lubricants based on the plant-based raw materials.
Polytetrafluoroethylene (PTFE) has a low friction coefficient and high chemical inertness, which makes it popular for the manufacture of tribological materials. However, its main disadvantage is low wear resistance. To improve the characteristics of PTFE, fillers are used, among which natural silicates, including palygorskite, are promising due to their availability, mechanical strength, and ability to improve tribological properties. Thus, the aim of the work is to develop polymer composite materials based on PTFE and natural palygorskite silicate with improved tribological characteristics. The starting materials were PTFE powder grade PN-90 and natural palygorskite of Ural origin. Structural analysis of the samples was performed using IR spectroscopy and scanning electron microscopy with energy-dispersive analysis, hardness was measured using the Shore A method. The results showed a significant improvement in the tribological characteristics of composites with palygorskite compared to the original PTFE. With the addition of 5 wt
Modern methods and equipment for testing and studying chain transmissions including specialized benches for testing bicycle drivetrains are considered. Advantages, limitations, and future development trends, such as the use of next-generation sensors and the automation of testing processes are considered. Special attention is paid to the standardization of testing and the adaptation of industrial methods to the specific needs of the bicycle industry and scientific research. It has been established that in most cases, the industry uses standard calculation methods and universal test machines, which explains a limited use of such testing benches and friction machines. Despite a widespread use of bicycle transport there is very little available literature concerning the wear and efficiency of bicycle chains. Thus, this paper can serve as a useful resource for professionals engaged in designing, testing, and analyzing the properties of material composing drive roller chains under the conditions of friction and wear.
The paper explains the need to combine synergetics and fractal analysis to study the contacting elements in friction and wear, as part of self-organizing into open systems dissipative structures known as a fractal behavior. The concept of multifractal analysis introduces the new quantitative parameters for the structures, characterized by a spectrum of generalized fractal dimensions and reflected by the degree of randomness. In accordance with the diversity of types of tribological process, various scenarios of system evolution seem possible. The most adequate description of these scenarios is achieved not in real physical space, but in a hypothetical space with ultrametric topology. Different levels of structures (micro, mesa, and macro scale) are described in the framework of multifractal analysis. It has been established that the frictional contact under study is a non-uniform fractal, that is, a multifractal. The procedure for calculating the multifractal dimension of this structure and the results of numerical calculations are presented, which confirm that the analyzed friction unit is a non-uniform fractal, i.e., a multifractal.
The purpose of the work was a comparative analysis of the results of metallographic and tribotechnical properties of industrial working rollers made of ShKh15SG steel (before and after operation) and IChKh28N2 wear-resistant cast iron (before operation) to select the material of the rollers and increase the service life of pendulum mills. Metallographic studies were performed on IM7000 optical microscopes with a Thixomet image analyzer and a microvizo-MET microimage. Microhardness measurements were carried out automatically using the Vickers method at a load of 50 g over the entire cross section of industrial rollers. Tribotechnical tests were performed on a SMC-2 friction machine according to the “roller–abrasive roller” scheme (rotation speed 500 rpm, load 45 N, test time 2 h) with an assessment of the coefficient of friction, wear, and surface roughness. It was found that ShKh15SG steel in its initial state had a homogeneous structure of low-pressure martensite with a carbide heterogeneity of (Cr,Fe)3C (HV 828) with an average hardness of HV 630. After 3 months of operation, under the influence of softening processes (temperature and plastic deformation), martensite was transformed into tempering troostite in the subsurface layers, and bands with martensitic and martensitic–troostite structures were formed with an average hardness of HV 443, which is 1.5 times less than the hardness (HV 630) in the initial state. Internal arc-shaped cracks were found. IChKh28N2 cast iron had a white pre-eutectic cast iron structure consisting of alloyed austenite (670–750 HV), cementite-type carbides (Cr,Fe)3C (856 HV), and complex carbides (Cr,Fe)7C3 (1389 HV). The average hardness of the cast iron was HV 781, which is 1.2 times higher than the hardness of the steel in its initial state. Tribotechnical tests have shown that cast iron had a lower coefficient of friction (0.58 versus 0.68–0.85 for steel), 1.7 times less wear (214 mg versus 358 mg for steel) and the ability to run in under friction (reducing the roughness of Ra by 3.7 times). Based on the structural characteristics, hardness, and tribotechnical properties, IChKh28N2 wear-resistant cast iron is recommended as a material for the manufacture of rollers of pendulum mills operating under conditions of intense abrasive wear, which will increase their service life.
The paper presents a comparative analysis of the tribological behavior of copper-based composite materials with different contents (30 and 50 vol
The paper evaluates the effectiveness of soft gas nitriding of alloyed structural steels 38KhMYuA, 38KhN3MA, and 38KhN3MFA, used in highly loaded gear transmissions, and establishes the limits of application of thin nitrided layers in terms of contact fatigue. The studies are conducted after nitriding at a temperature of 580°C and a duration of 7 hours using microhardness testing, layer-by-layer chemical analysis by high-temperature gas analysis, X-ray structural analysis, and contact fatigue testing of rollers simulating rolling and sliding conditions, typical for helical gearing. It is found that soft nitriding ensures the formation of a hardened layer 0.18–0.25 mm thick with a microhardness of 4.8–5.5 GPa while maintaining a ductile core with a hardness of 240–260 HB. It is shown that under elevated contact stresses, failure of nitrided samples initiates in the subsurface layers and develops via a deep contact fatigue mechanism, accompanied by the formation of deep spalling and a so-called white etching area. The results obtained demonstrate the limited effectiveness of thin nitrided layers under high contact loads and point to the feasibility of using materials with thicker hardened layers (0.8–1.2 mm) or design and technological solutions aimed at reducing contact stress and increasing the service life of gears.
The article presents the results of a study examining the effectiveness of copper ion implantation in the steel surface for a similar friction pair without lubricant. It is shown that under steady-state friction conditions with implanted ions at irradiation doses of 1017 and 5 × 1017 ion/cm2, the steel wear resistance increases by 2 and 1.5 times, respectively. The effect of preliminary implantation of iron ions at a dose of 1016 ion/cm2 is examined. It is found that the use of preliminary implantation leads to a 2.5-fold increase in wear resistance. The friction surface of samples pre-implanted with iron ions exhibits minimal damage and the highest wear resistance. The article describes structural changes in the surface plastic deformation zone during sliding friction of steel with a copper-based coating. It is shown that the increase in wear resistance is associated with the presence of a “long-range effect,” which contributes to an increase in the wear resistance of surface layers. The mechanism of the long-range effect in ion-alloyed metallic materials under contact deformation conditions is discussed.
This article examines the problem of increasing the wear resistance of materials. The primary objective of the study was to experimentally validate the effectiveness of 3D-printed porous polymer structures impregnated with lubricant to improve tribological performance by retaining the lubricant within the pores without chemical interaction with the base material. Experimental samples were fabricated from two types of polymers: polylactide (PLA) and acrylonitrile butadiene styrene (ABS), with a fill density of 90
By using the finite element method, the effect of loading exerted on the stress–strain state of reinforced metal-fluoroplastic plain bearings under static and dynamic loading conditions has been investigated. Metal-fluoroplastic bearings are considered as three-layer composites. Stresses and strains in the, antifriction and adhesive layers, as the main ones responsible for the bearing capacity under load, are studied. The difference in the stress-strain state under static and dynamic loading conditions of bearings is demonstrated. It has been established that the load capacity of bearings under dynamic loading depends on a ratio batween the effective stress– strain level and the strength characteristics of the adhesive layer material. The obtained results of calculations are compared with experimental data. The satisfactory correlation between the calculated and experimental data makes it possible to use this method for to determine the dynamic load capacity of plain bearings.
This article examines the gear transmission of a two-stage gearbox as a tribological system whose performance is determined by friction conditions and the contact fatigue endurance of the tooth surfaces. The geometric parameters of the transmission were calculated and contact and bending stresses were analyzed using the APM WinMachine software package. It was shown that when using steel 45 with heat treatment—hardening with high tempering, the acting contact stresses reach the maximum permissible values, which leads to intensive wear and a short transmission life. To improve durability, it is proposed to replace the gear pinion and wheel material with 20CrNi structural alloy steel with a chemical-thermal carburization treatment, which reduces the relative level of contact stresses and increases contact endurance. An analysis of the influence of loading cycle parameters on the contact and bending stresses determining the nature of tooth wear is conducted. It is shown that for cemented gears, the calculated fatigue stresses do not depend on the cycle parameters, which indicates increased stability of the tribological characteristics of the transmission.
The work is devoted to studying roller knives made of Kh12MF tool grade steel with a nickel–copper coating applied by means of diffusion alloying and a subsequent intensive plastic deformation (IPD) under contact stresses ranging from 3.0 to 4.5 GPa. In the course of the studies, such methods as optical and transmission electron microscopy; X-ray diffraction and microrentgenospectral analysis have been used. Tribological and corrosion testing, as well as microhardness and roughness measurements have been carried out. It is shown that after applying Ni–Cu coating and IPD at a stress of 3.5 GPa, not only a twofold decrease in the coefficient of friction, 2.1-fold decrease in wear level, 2.5-fold decrease in the roughness of the roller surface, as to compare to uncoated steel, but also an increase in the seizure load up to 1400 N have been observed. At the same time, a dislocation substructure has been formed in the coating with a minimum size of coherent scattering regions amounting to 23 nm and a maximum level of crystal lattice microdeformation being of 1.25
The article is devoted to the study of the prospects of using aluminum alloy parts with an oxide-ceramic coating applied to the friction surface by the method of microarc oxidation in friction units operating due to lubrication by the liquid medium in which they operate or which is pumped by this mechanism. Such mechanisms and friction units include elements of pumping and compressor equipment used in the oilfield industry (shut-off valves, parts of centrifugal, vane, slide, gear and other pumps, and some threaded connections). In this situation, the coupled friction surfaces are constantly lubricated by the working medium (water, oil, water–oil emulsions). Tribotechnical tests were carried out on a laboratory installation, the friction unit of which consisted of a rotating roller made of aluminum alloy of the AMg6 brand and a tape made of aluminum foil of the AD1 brand with a thickness of 100 microns sliding along it. An oxide-ceramic coating was applied to both parts by microarc oxidation. A solution containing liquid glass in the amount of 13 g/L and potassium hydroxide in the amount of 2.5 g/L was used as the electrolyte. The oxidation process was carried out in a symmetrical anode-cathode mode using industrial alternating current with a frequency of 50 Hz at a constant current density of 6 A/dm2 to a final voltage of 400 V. Laboratory tests have shown that aluminum alloy parts with an oxide-ceramic coating can be successfully used in friction units characterized by low contact pressures and sliding speeds. At the same time, the very high corrosion resistance of oxide-ceramic coatings protects friction units from the effects of aggressive media (reservoir water with increased mineralization, water-oil emulsions containing hydrogen sulfide, and carbon dioxide), as well as from abrasive particles always present in the extracted and accompanying fluids. The use of aluminum alloys in friction units with a surface hardened by microarc oxidation will reduce the weight of pumping and compressor equipment, for example, submersible multistage pumping units, which reduces the cost of lifting operations, and will also improve the operational reliability and durability of oilfield pumping and compressor equipment.
This paper presents a method for determining the friction coefficients of an antifriction coating based on silver with the addition of molybdenum disulfide or graphite in vacuum. The method for determining the coefficients of friction is implemented at a vacuum tribometer. The dependences of the friction coefficients in the contacting pair consisting of steel ShKh-15 and an antifriction coating based on silver with the addition of molybdenum disulfide and, in another case, graphite, were obtained depending on the ambient pressure. The values of the average friction coefficient in a pair of a ball made of ShKh-15 steel and a ring with an antifriction coating containing 94
Despite high thermal-oxidative stability and chemical inertness, standard perfluoropolyether lubricants are susceptible to catalytic decomposition at high temperatures in the presence of metals, leading to corrosion and limiting their use. A solution to this problem may be the use of perfluoroalkyl-substituted triazines, which exhibit significantly higher corrosion-oxidative stability. The aim of this study was to evaluate the feasibility of using synthesized perfluoroalkyl-substituted polytriazines (PFPT) with molecular weights ranging from 932 to 2920 as lubricants and compare their tribological properties with those of the commercial perfluoropolyether (PFPE). A number of PFPT samples (bis-triazines and oligotriazine) were studied by DSC and TGA methods and boiling points were determined. Tribological tests were carried out using the plane-to-plane design (ShKh15 steel/12Kh1 steel) at room temperature. The average friction coefficient (fav) was determined for each PFPT sample, with fav consistently increasing with increasing PFPT molecular weight. It was shown that the friction coefficient of PFPT (0.12–0.18) is comparable to that of PFPE (0.13) and significantly lower than that of dry friction (0.27). The results confirm the potential of PFPT as chemically inert and thermally stable lubricants. Their tribotechnical characteristics are comparable to those of commercial PFPE, indicating the possibility of combined use or replacement.
Results of evaluating the tribotechnical characteristics of polymer composite materials based on low-density polyethylene PE273, modified with various fillers: polyethylene wax (5
A new approach to measuring wear in sliding friction units based on the use of cluster analysis of acoustic emission signals accompanying the operation of the triboassembly is proposed and experimentally investigated. A special feature of the proposed approach is that the contribution of each mechanism of damage to the friction unit, which is identified in a multidimensional field of acoustic emission features with a time reference for their manifestation, is considered in the total wear, which makes it possible to trace the dynamics of wear of the friction unit directly during observation (measurement). The study was conducted by comparing the use of two promising threshold-free clustering algorithms for acoustic data relative to the standard amplitude threshold method for detecting and identifying acoustic emission events, which allowed us to gain an idea of the advantages of the proposed approach in comparison with the current level of development of this type of technology. The results have shown that the use of multiparametric cluster analysis to detect the type of damage (wear) mechanism allows for at least 45
The elemental composition and chemical bonds in a diamond-like carbon film on the surface of a tungsten–cobalt alloy base were studied using X-ray photoelectron spectroscopy. The ratios of sp2/sp3 bond fractions were determined using various parameters of the CKLL Auger spectra excited in X-ray photoelectron spectrometers; the average values were 0.32/0.68. It was revealed that the tribological interaction of a counterbody in the form of an aluminum oxide ball with the base material begins with a friction coefficient of approximately 0.4, and with the diamond-like film surface with a friction coefficient of approximately 1.0. With further sliding, starting from approximately 25,000 sliding cycles, the friction coefficient with the tungsten-cobalt base increases to 0.65, and the friction coefficient with the diamond-like film drops to values of 0.50. In the range of 20 000–25 000 sliding cycles, the friction coefficient of the counterbody on the diamond-like film drops to 0.32, then returns to 0.62. The values characterizing the wear of the counterbody when interacting with a hard alloy base are higher than when interacting with the surface of the diamond-like film. The results confirm that films of this type are technologically feasible for use in friction units that require a combination of high deformation resistance under heavy loads and high corrosion resistance at high temperatures and in adverse environmental conditions.
The purpose of the study is to determine by the finite element method the stress-strain state and behavior of contact interaction characteristics under various loading conditions of the liner-shaft system, which is used for materials research when operating under conditions of frictional and mechanical fatigue. The cases of loading the system with different ratios of contact forces applied to the liner and bending forces applied to the shaft are considered. Verification of the results is carried out using beam theory and contact theory. According to the results of the study, it is shown that depending on the direction and magnitude of the bending load, it is possible to form a contact area of three different shapes: rectangular, elliptical, and divided into two parts. Furthermore, optimal load ratios minimizing the von Mises stresses were identified: in the liner with co-directed Fb and FN at a ratio of FN/Fb = 20–50 (e.g., at FN = 500 N, Fb = 25 N); in the shaft with oppositely directed Fb and FN at a ratio of FN/ Fb = 20 (e.g., at FN = 500 N, Fb = 25 N). Thus, the presented approach to modeling volumetric damage in a friction pair, one element of which is loaded by a non-contact force, provides an opportunity to solve optimization and damage management problems for complex technical systems by controlling boundary conditions without costly design or material changes.
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.
