AbstractThe results of a study of the friction and wear characteristics of the developed nanostructured glass-composite self-lubricating detonation coatings with the composition SiC–Ni–Cu–Al–Si–C additionally containing a SiO2–Al2O3–B2O3 aluminoborosilicate glass phase and structurally free MgC2, which forms α‑graphite during thermal decomposition are presented. It is indicated that their synergistic effect promotes the creation of an antifriction surface layer that minimizes contact parameters. An increase in the adhesion strength of the coatings is achieved by preliminarily applying a sublayer of glass-like sodium silicate Na2O(SiO2)2 onto the working surface. It is noted that the intercalation of the graphite layer by the particles of the subsurface zone does not affect the tribotechnical characteristics of the coatings. The developed coatings show high performance properties; here, the way of wear stabilization is the presence of a thin-film antifriction layer based on α-graphite, which shields unacceptable processes of molecular adhesion interaction.

AbstractIn this paper, we present the evaluation results of the tribotechnical characteristics of a dry friction pair of 30KhGSN2A steel (CSN 16532)–30KhGSN2A steel (CSN 16532) at pressures up to 350 MPa using KE-4 and UMT-1 laboratory friction machines, as well as a special stand simulating a real hinge-bolted connection. The surface of the steel shafts was processed by electrospark alloying (coatings were made of BrAZhMts10-3-1.5 and BrMtsF3 bronzes) and ion implantation (a copper ion beam was used). It is shown that, the minimal values of the friction coefficient (~0.10) are observed for a pair with a BrMtsF3-6 coating under laboratory test conditions at 150–200 MPa and (~0.13) for a pair with a BrA-ZhMts10-3-1.5 coating at 200–250 MPa; wear is reduced by 1.5–2 times. Under the stand test conditions, it was obtained that the increase in the wear resistance of steel is 1.5, 1.7, and 5.7 times and the decrease in the friction coefficient is 1.3, 1.5, and 3.1 times for friction pairs with a coating of BrA-ZhMts10-3-1.5, BrMtsF3-6, and copper, respectively. An improvement of tribotechnical parameters of steel friction pairs is largely due to the “long-range action” effect that manifests itself during high-energy treatments.

Abstract—Conditions for seizing during hydrodynamic contact between parts under rolling friction have been studied. For this purpose, a known friction model based on the generalized Eyring equation and taking into account the phenomenon of oil film self-heating has been used. The fact that a correct description of friction curves using this model is possible has been confirmed by comparison with published experimental data. Conditions are revealed, under which in the thermal zone of friction curves, despite a decrease in the friction coefficient, an increase in friction power loss continues. It is shown that the bearing seizing hazard occurs when the bearings operate in a thermal zone of the friction curves. A concept of critical slide–roll ratio that represents a boundary of the thermal zone of friction curves has been introduced, and its dependence on the contact pressure and temperature has been studied for PAO1 grade polyalphaolefin oil in the temperature range of 40–100°C and for MN-7.5u grade oil in the range of 60−140°C. It is shown that the critical sliding-to-rolling ratio increases with decreasing contact pressure in the bearing, as well as with increasing oil temperature. It is concluded that the conditions of contact between the rollers and the inner ring promote an increase in friction power loss to a greater extent than the conditions of contact between the rollers and the outer ring. This indicates a higher seizing hazard in the case of the inner ring than in the case of the outer ring, which is confirmed by the statistics of rolling bearing failures. In order to prevent seizing in bearings, it is necessary to provide a margin with respect to critical sliding at the bearing design stage.

Abstract—The erosion of a straight cylindrical tube by the example of a small caliber (30 mm) laboratory smoothbore ballistic unit during experimental gas dynamics studies is considered. For its diagnostics a non-contact analog-to-digital measuring device allowing for determination of the coordinate of the measured section and a software package for processing the obtained data were developed. A geometric model of the detecting unit with the location of three distance sensors in the vertices of a regular triangle is presented. A prototype of the device was assembled and tested, which allows measuring the internal diameter of the smooth bore channel of any length with a caliber of 30 mm and to record the results in the computer memory in real time. Quantitative erosion of the breech face after a series of tests is given. To compare the results, a comparison is given with the readings of a certified bore micrometer. The results of gas-dynamic analysis of one of the experiments are presented in the form of diagrams of maximum pressure, gas temperatures, and the inner surface of the barrel. The highest pressure and temperature values occur at the breech face compared to the entire length of the barrel, which confirms the erosion profile. In this case, the temperature of the inner surface of the channel is much lower than the melting temperature of steel. However, in some experiments, the internal surface temperature reached a value of 980 K and higher. At this value, the strength of the steel becomes comparable to the shear stresses of the gas flow, which causes detachment and entrainment of metal particles. The use of the developed device and software package makes it possible to improve operational safety, as well as to reduce time and material costs for repair and maintenance of installations.

Abstract—Currently, the choice of wear-resistant pipes is based on the wear resistance of the material and is not accompanied by consideration of the design properties. Polyethylene pipes are widely used for hydro-transportation of suspensions. In order to more fully inform consumers of polyethylene pipes about various levels of wear resistance, the Polyplastic group is developing a range of pipes with a calculated wear resistance resource. An indicator of the calculation of the wear resistance resource is the length of the flow of suspensions, which, passing through the pipeline, wears out the wall by 75%. To determine the estimated resource, data on the decrease in wall thickness during the passage of the flow are required. The only internationally recognized method to determine this value is the EN 295/3 method [1] using a ribbed abrasive, which was used as a reference method in this study.

AbstractThe article studies the characteristics of mill knives of high-speed steel HS 18-0-2-5 with as well as without МоС and Мо2С molybdenum carbide coating at plane milling of oak wood. The molybdenum carbide coating was deposited by arc vacuum physical vapor deposition (Arc-PVD). The knife edge wear was determined using a contour measuring system for determining the displacement of the cutting edge along the axis of the cutter wedge sharpness angle (WBW). Compared to a milling cutter with knives without coating, the molybdenum carbide coating improves the wear resistance of the knife blades and increases the cutting power by almost 40% when milling oak wood samples. The mills with the knife edges coated with the molybdenum carbides exhibited an average reduction in oak wood surface roughness Ra by 1.5–3 µm as compared to the bare tool in the entire range of applied feed rates and milling length. The laboratory tests of the wood-cutting tool covered with MoC coating prove that their durability has increased by 30% against the durability of the bare tool used in milling oak wood.

AbstractThe study investigates the relationship between electrification of bodies and tribochemical processes of destruction of a composite material. The evolution of secondary surface structures is studied by ATR IR spectroscopy. It is found that the transfer films consist of fragments of the epoxy-diane matrix. The onset of electrification during friction of metal–polymer systems is due to the transfer of radicals and ions formed as a result of the destruction of organic molecules by homo- and heterolytic mechanisms. It is shown that the heterolytic destruction prevails at the initial stage of friction. Oxidation of free radicals is accompanied by the appearance of C=O bond vibration bands in the IR spectra. Modification of the epoxy-diane matrix with particles with a spinel structure activates the formation of secondary surface structures in metal–polymer triboconjugation. The potential difference between the bodies does not disappear even after a long time after the end of the friction process due to the presence of charges fixed on the surface. The main contribution to electrification in metal–polymer systems is made by the transfer of ions rather than electrons.

Abstract—The influence of dispersed filler in the form of foundry coke on the wear resistance of polytetrafluoroethylene-based composite has been studied by the method of molecular dynamics. The application of this method made it possible to investigate the causes of increasing the wear resistance of the polymer composite at the molecular level. Two-layer molecular models of PTFE and its composite F4K20, consisting of 80 vol % PTFE + 20 vol % foundry coke were made. Computer simulation of wear product separation from two zones located in the tribocontact area has been performed. Differences in values of energy values of intermolecular interaction depending on the initial position of the separated molecules are shown. It was found that the energy value of intermolecular interaction determined by simulating the surface fracture of F4K20 is more than 30% higher than that determined for PTFE. The calculation of internal friction force in models of PTFE and F4K20 has been carried out. It was found that the internal friction force calculated at the molecular level in F4K20 is significantly higher than the same parameter calculated for PTFE. Visualization of the fracture process of the constructed models was carried out. It is noted that only PTFE molecules are observed when molecules are separated from the surface of both models. If the fracture process of F4K20 includes the near-surface region, the separation of foundry coke molecules is additionally initiated. As a result of the investigations a numerical estimation of change of characteristics of intermolecular interaction with the introduction of a filler into polymer resulting in more than two degrees increased wear resistance of PTFE-based composites is given, which is noted by many researchers. The research results can be used for the development of new composite materials including nanocomposites.

Abstract—The wear of PTFE/SiO2 composites on steel 40X with low and steel 40X13 with high chromium content is studied. Tribochemical processes occurring during the wear of the composite are characterized by changes in the chemical structure and composition of the running film of the composite using attenuated total reflection technique of FTIR spectroscopy and DTA results of thermal oxidative degradation of model blends of PTFE with iron, chromium and silicon oxides. It is found that higher wear rate of the composite on the stainless steel is accompanied by a lower extent of oxidation/chelation of the polymer and a greater content of accumulated silica in the running film, while at friction on the low chromium steel a lower wear rate is matched with higher content of oxidation/chelation products, lower accumulation of silica in the running film and appearance of double bonds, indicative of the polymer defluorination. The principal differences in wear rates and running film composition are attributed to the catalysis of PTFE defluorination and oxidation by iron oxides of the low chromium steel counterface, based on IR-spectroscopic evidence of similar chemical changes in PTFE on sintering in presence of Fe3O4, as well as DTA results showing catalysis of PTFE degradation in air and nitrogen in presence of nano-Fe3O4 and drastic improvement in wear resistance of PTFE/silica composite modified with small addition of nano-Fe3O4. It is hypothesized that the sharp increase in the wear resistance of PTFE nano- and microcomposites, containing highly abrasive particles, at friction on a stainless steel, observed by several research groups, is due to the destruction of a mechanically strong passivation surface layer of chromium oxide of the counterbody and the entry of freshly formed iron oxides into the friction zone, which catalyze the tribochemical oxidation of PTFE and improve the transfer film adhesion and life.

Abstract—A method of designing bevel gears is given, allowing to reduce the specific sliding ratio. Specific pressure coefficients are used as an additional evaluation criterion. The mathematical relationship between the criteria used is given. A distinguishing feature of the proposed methodology is the possibility of calculating the gears using an arbitrary coefficient of profile shift for each of the gears. In doing so, the value of the radial gap equal to 0.25 of the module is retained in the gears. The Bevel Gears x64 program is used for calculations. This program was written as part of the ongoing research. As an example, it is shown that a gear with number of pinion teeth z1 = 16 and number of wheel teeth z2 = 20, with the coefficient of profile shift for pinion x1 = 0.7 and for wheel x2 = 0.7, has relatively low and fairly close values of specific sliding ratio |λ1max| = 1.213 and |λ2max| = 1.214 as well as specific pressure ratio ϑ1 = 0.45 and ϑ2 = 0.347. In similar gears (z1 = 16, z2 = 20), designed according to the standard methodology (x1 = 0.17 and x2 = –0.17), the values of the studied indicators were |λ1max| = 3.165, |λ2max| = 2.512, ϑ1 = 0.942, and ϑ2 = 0.572. Reducing specific sliding ratios |λ1max| from 3.165 to 1.213 and |λ2max| from 2.512 to 1.214 will reduce the slippage of tooth dedendum on the pinion and wheel in proportion (2.6 and 2.1 times, respectively). The results show a significant increase of wear-resistance of the designed gears.

AbstractIn this paper, we present a theoretical solution to the problem of finding the microgeometry of the friction surface, which ensures uniform wear of the friction pad of the brake mechanism and the immobility of the crack in the material. As is known, the friction pair of the brake mechanism wears unevenly, so it is advisable to reduce wear where its value is maximum. It is possible to achieve this goal by applying design and technological methods at the stages of designing and manufacturing a friction pair if the optimal microgeometry of the friction surface of the pair is known. The desired optimal microgeometry of the friction surface of the friction pair must also prevent the growth of possible cracks in the material. The stated optimization problem is solved using a model of a rough friction surface. Using the perturbation methods, the theory of analytic functions, and least squares, the problem is reduced to a problem for a conditional extremum of a function of many variables. A closed system of algebraic equations, which makes it possible to obtain a solution to the optimization problem for the friction “pad-brake drum” pair depending on the characteristics of its elements, was constructed. The resulting microgeometry of the friction surface provides an increase in the wear resistance and bearing capacity of the friction pad of the vehicle brake mechanism.

AbstractThe effect of a ratio between Al and Fe in the electrode mixture exerted on the phase composition, tribotechnical properties, corrosion behavior, and oxidation resistance of electrospark Fe–Al coatings on AISI 304 stainless steel have been studied. Five mixtures of granules with an aluminum concentration ranging from 20 to 100 mol % have been prepared. The structure of the coatings has been studied by means of XRD analysis, scanning electron microscopy, and energy dispersion spectroscopy. The wear resistance of the coatings has been studied according to the ASTM G99-17 standard in the course of dry sliding friction using disk-shaped riders made of R6M5 grade high-speed steel at a velocity of 0.47 m/s under a load of 10 N. The oxidation resistance test was performed at a temperature of 900°C for 100 h. It has been found that with increasing aluminum content in the mixture of granules, the aluminum concentration in the coatings exhibits a monotonic increase, and the phase composition of the intermetallic compounds changes from FeAl to Fe14Al86. The microhardness of the coatings ranges from 5.8 to 7.1 GPa. The average friction coefficient of the coatings is in the range from 0.71 to 0.87. The wear rate of Fe–Al coatings ranges from 2.3 × 10–5 to 7.9 × 10–5 mm3/(N m). The coating with the lowest aluminum concentration exhibits the best wear resistance, whereas its wear rate is 4 times lower than that of AISI 304 grade steel. The oxidation resistance of coated stainless steel increases with increasing iron concentration in the mixture of granules. The results of testing have shown that the coatings obtained in the anode mixture with 20 at % of aluminum can provide a 13-fold increase in the oxidation resistance of AISI 304 grade stainless steel. Testing the samples by means of potentiodynamic polarization and impedance spectroscopy in 3.5% NaCl solution have shown an increase in the corrosion resistance with increasing aluminum concentration in the coatings.

Abstract—Wear of the contact surfaces is an important characteristic of rib-roller end interaction of roller bearings. The purpose of this study was to develop effective methods for calculating the wear rate of these surfaces under alternating dynamic loads. In wear rate calculations of bearing parts, as a rule, Archard’s law is used since it has been verified in hydrodynamic friction testing of bearing steels. In the paper, based on this law, a direct step-by-step wear rate calculation method for rib-roller end contact at variable loads and sliding speeds is developed. According to it, normal force, sliding velocity, and contact oil film thickness are determined in bearing dynamic modeling, and the finite element method is used to calculate contact pressure fields. A multi-mass bearing dynamic model includes a contact friction model, which allows an adequate description of hydrodynamic contact behavior of solid bodies. Using the bearing life dependence on the oil film parameter and experimentally measured steel bearing wear rates, the dependence of wear coefficient on the oil film parameter is obtained. The direct calculation method involves many computations, which makes the influence of individual factors on wear rate non-obvious. In this regard, a method of wear rate calculation with averaged parameters is also proposed. Using these two methods, rib-roller end wear calculations for a double-row tapered roller bearing are implemented. The spherical shape of the roller end and conical, toroidal convex, and concave shapes of the rib are considered. Comparison of wear rates obtained by the two methods confirms the acceptable accuracy of calculations with averaged parameters. The results in particular demonstrate that a toroidal concave rib surface allows reducing the wear rate up to three times in comparison with the tapered surface.

Abstract—The effect of 2,2,6,6-tetramethylpiperidine (TMP), 2,6-di-tert-butyl-4-methylphenol (DTBMP), para-cumylphenol (PCP), 2,2,6,6-tetramethylpiperidine-1-oxyl (TMPO), and dicumyl peroxide (DCP) on the anti-wear properties of dodecanethiol (DdSH), didodecyl disulfide (Dd2S2), and dibutyl disulfide (Bu2S2) in a solution of purified Vaseline oil (PVO) has been investigated. The anti-wear properties of 23 two-component compositions of additives from 28 possible combinations were studied. A rule was proposed: synergy is when the effectiveness of a mixture of additives is greater than the average result of the sum of anti-wear efficiencies of each component separately, and antagonism is when the effectiveness of a mixture of additives is less than the average result of the sum of anti-wear efficiencies of each component separately. The practical significance of the proposed method for studying two-component additives is that it can be used to confirm or refute the mechanism of action of additives.

Abstract—This article describes the analysis of influence of biocarbon (BC) produced by pyrolysis from a pine nutshell on tribological properties of friction material. The research object has been presented by copper-based friction material doped with 12% tin with 10–40 vol % of carbon additive in the form of BC. The average particle size of BC is 10 μm. The tribological properties has been analyzed using an IM-58 friction machine. The tribological tests demonstrate that with an increase in the BC content the dynamic friction coefficient increases from 0.041 to 0.066. With the aim of comparison, addition of GE-1 grade powdered graphite results in an increase in the friction coefficient from 0.038 to 0.069. Simultaneously with the increase in friction coefficient the wear of friction material also increases not exceeding its ultimate value. Thus, at 10 vol % of BC addition the wear is 4.0 μm/km, at 40 vol %, 12.1 μm/km. Analysis of surface morphology of bronze demonstrates that the BC particles are worn uniformly with bronze layer, retaining the initial porous structure. The products of BC destruction with sizes of 50–500 nm have been introduced into the surface layer of bronze. The results demonstrate opportunities of biocarbon additive in friction material, which can be used as a substitution of conventionally used graphite. It should be mentioned that the promising opportunities of BC addition to powdered antifriction material are determined by initial raw material for its production.

Abstract—This article discusses the influence of compositions based on polyfluorinated alcohol immobilized on montmorillonite clay and Fluralite polytetrafluoroethylene on wear resistance of polyurethane elastomer filled with these substances. It has been established that introduction of the mentioned fluorinated modifying agents results in rearrangement of the amorphous structure of the polymer matrix, thus improving wear resistance. The developed fluorine containing polymer composite materials can attract interest as coatings of various purposes as well as elements of lip seals.

AbstractThe structural parameters of subsurface microvolumes of copper alloys (intrinsic X-ray lines broadening and the solid solution lattice parameter, the degree of frictional hardening) during friction in the medium of active and inactive lubricants are considered. Their variations under the conditions of contact deformation are experimentally shown and an interpretation of the influence on tribological characteristics (running-in ability, wear rate) is given. The structural parameters and their adaptation to friction loading conditions are compared with the running-in ability, adaptability, and wear resistance of antifriction alloys and their relationship is revealed, which manifests itself in a joint change in structural and tribological parameters depending on the composition of antifriction materials and the nature of lubricants. Recommendations on the selection of the composition of antifriction copper alloys for friction units are given: for aluminum bronzes used as a material for heavily loaded pinned joints, the operation of which runs in a medium with surface-active lubricant components, long-term performance is ensured by a single-phase alloy with a large margin of plasticity (BrA5, BrA7).

Abstract—The friction surface is a concept that has established itself in tribology and the definitions of friction processes. It is clear that this is a tribute to the traditional logic of continuum mechanics. On the other hand, the physical and materials science logic of the real formalization of the concept of surface determines its concretization, which differs from conditional geometricity. In the proposed article, the author, having previously considered the general structural and energy patterns of the evolution of rubbing surfaces, comes to the concept of a critical volume of friction, which is adequate to the concept of equilibrium roughness. The author defines this volume as the volume of an elementary tribosystem. This volume within the framework of the model of the moving critical volume of friction is an elementary tribotransformer of energy. An elementary tribosystem is formed as an adaptive response of a deformed rigid body under friction, the smallest volume that has accumulated the potential energy of defects of extreme density. It has an internal equilibrium far from the state of initial equilibrium. Further, this volume evolves structurally with the constancy of its size. An attempt is made to physically model this critical equilibrium volume of friction. A model of ideal equilibrium of the volume of an atomically smooth surface within a certain elementary nominal friction area adequate to the volume of equilibrium roughness is considered. A method for calculating this critical and equilibrium friction volume is proposed. The principle of extrapolation of the equilibrium volume (oscillation amplitude) of an atomically rough surface to the temperature of absolute zero is substantiated. The direct correlation of the size of the critical friction volume with the size of the equilibrium roughness of the rubbing surfaces is shown. A refined calculation of the critical size of friction—an elementary tribosystem in the state of its ideal evolution according to the model of a mechanical (nano) quantum as an elementary subtribosystem is performed.

AbstractAtomic structures arising during the vacuum deposition of TiAlN nanocoatings on the iron surface are studied using quantum chemistry methods. The effects that appear during the deposition of the first atomic layers of such coatings are considered. Calculations of the bond strength of such coatings with the surface are carried out. Within the framework of the model used in this study, it is shown that the most durable is the coating, the lower layer of which consists of Ti atoms, located directly on the iron surface. The upper layers consist of a mixture of Ti, Al, and N atoms. The bond strength of such a coating with iron can increase by 13% compared to its bottom value. When modeling the interaction of the coating with the substrate, it is has been established that the strength of the bond between the components is almost independent of the substrate thickness, if the substrate consists of three or more iron atomic layers. This fact testifies to the short-range nature of the interatomic forces at the coating–substrate interface, which greatly simplifies the theoretical analysis of the strength properties of such systems. The paper shows that when calculating the atomic configurations appearing on the iron surface during vacuum deposition, it is necessary to look for configurations with a minimum energy. It is these configurations that are most likely to form on the substrate surface. Traditional methods of studying atomic structures based on the principle of the minimum system enthalpy are not applicable in this case. The results of this study are compared with known experimental data related to similar objects.

Abstract—The article suggests a disc brake design with carbon friction materials (CFMs). The principle of the method is to create two friction units in the disc brake with materials placed in them that have different frictional properties. The two friction units are created by separating the brake disc with a thermally insulating screen. One friction unit (friction unit A) has CFMs installed having a low friction coefficient in the initial temperature mode and a high friction coefficient at a temperature of 300°C or higher. The other friction unit has a premium-class car block (CB) and a steel disk (35GS steel) the friction coefficient of which does not depend on temperature (friction unit B). The experiment conducted justifies the creation of a disc brake based on the described principle. The experiment was carried out on a testing bench that simulates the interaction of the disc brake as per the load-speed criteria. The testing bench creates conditions for a constructive separation of the brake disc into friction units A and B. As an example of two friction units: CFM–CFM (friction unit A) and CB–steel 35GS (friction unit B). The experimental performance of the friction coefficient versus temperature obtained on the testing bench in relation to friction units containing friction materials CFM–CFM and CB–steel 35GS showed that the friction coefficient of the disc brake takes high values in the entire range of temperatures tested during braking. The article offers a promising design of a disc brake with thermally insulated friction units. The design consists of two brake discs and a central part, which is thermally insulating. All parts are glued together.