Journal of Friction and Wear最新文献

Modification of ceramic coatings developed for friction units is an important area of research aimed at improving their tribological characteristics. This paper presents ceramic coatings formed on B95 and D16 aluminum alloys by the microarc oxidation (MAO) method in a single-stage technological process with inclusions of Al–Cu–Fe quasicrystals. The technology of rubbing quasicrystals into the coating surface during final polishing was also used. Friction and wear tests were carried out according to the ASTM G99 standard paired with a tungsten carbide ball. Analysis of the surface and cross sections by the SEM microscopy method showed that the modification affects the coating structure. Quasicrystals are concentrated in the pores and participate in the friction process. Addition of a small amount of modifier to the electrolyte, as well as the rubbing technology, make it possible to reduce the friction coefficient and wear rate compared to purely ceramic coatings obtained on the B95 alloy. A larger amount of modifier gives a negative result. Adding a modifier to the electrolyte when forming coatings on D16 alloy leads to an increase in the friction coefficient and a decrease in wear resistance.

M1 Copper samples with different structural states were obtained by equal-channel angular pressing and subsequent annealing. The structure of the samples before and after sliding friction tests was studied by transmission electron microscopy and metallography. The mechanical characteristics of the samples were determined during tensile tests and nanoindentation. During friction according to the ball-on-disk scheme, the friction coefficient, vibration, and acoustic emission were recorded to identify the features of the influence of the structural state of the material on the friction dynamics. Confocal laser scanning microscopy was used to assess wear. It was found that an increase in the number of equal channel angle pressing (ECAP) passes and annealing have an insignificant, no more than 8%, effect on the sliding friction coefficient in the steel–copper pair. It is shown that an increase in the number of ECAP passes can reduce the wear of M1 copper by 26–93%. After annealing at a temperature of 200°C, wear is additionally reduced by 5–8%, compared to samples without annealing. Annealing at 300°C leads to an increase in wear by 37–65%, compared to samples without annealing. Low plasticity and high hardness of the material in a highly deformed state lead to the formation of a thick surface layer consisting of a mixture of oxidized wear particles, copper oxides, and fragments of the destroyed friction surface. Annealing at temperatures of 200 and 300°C contributes to less pronounced destruction of the surface of the samples, as well as oxidation and mixing with wear particles in a thinner surface layer. The results indicate a significant effect of the structural state on both the mechanical properties and the features of the sliding friction and wear process of M1 copper.

Currently, the quality of an abrasive tool is usually estimated directly under the production conditions of the consumer enterprise, which is associated with methodological difficulties, time costs, and often insufficient objectivity of control due to the impossibility of analyzing a large sample of test wheels. The lack of modern methods and means of technology control in the production of tools does not guarantee the stability of their quality, including the wear resistance parameter, which predetermines the durability and grinding coefficient of the wheel. The purpose of the study is to find the possibility of express quality control of an abrasive tool made of electrocorundum material according to the criterion of relative wear resistance. Tests have been carried out and the results of wear resistance and energy efficiency of grinding various samples of abrasive wheels by the method of abrasion against a counterbody have been obtained. It has been shown that the use of the Shlif-3 modernized device allows for express quality control of an abrasive tool, including determining the relative wear resistance. A correlation between this indicator and the operational and technological characteristics of the tool has been established.

The analysis of the structural model of composites developed for the case of dispersion of fillers in the polymer melt is carried out. It is shown that the use of the expression for determining the matrix loading characterizing the share of external applied load falling on the matrix is not effective enough for comparative assessment of wear resistance of developed composites at the same concentrations and average sizes of dispersed fillers but consisting of different materials. For the possibility of a refined assessment of wear resistance of such composites, an additional criterion taking into account the energy characteristic of interaction between matrix and filler at the molecular level is proposed. Computer modeling of the molecular structures of polyetheretherketone and its two nanoscale composites containing fullerene and nanoscale copper was carried out to determine the shear modulus and intermolecular interaction energies in the volume of the materials under study and at the matrix–filler interface. It is noted that the introduction of nanoscale fillers increases the values of shear modulus and volumetric energies of intermolecular interaction. At the same time, the most significant increase, by more than 2.5 times, was noted in the value of the energy of intermolecular interaction at the interface of the matrix–filler phases in a composite containing nanosized copper, compared with a composite containing fullerene. Thus, this parameter is proposed as an additional parameter for assessing the wear resistance of nanoscale composites at the stage of their development.

The aim of this work was to analyze the wear resistance of composite ion-plasma coatings and substantiate methodological approaches for its prediction. The object of the study was multilayer 2D-nanocomposite coatings of the TiN/AlN system with a total thickness of 0.8–4.0 μm. The coatings were applied using vacuum ion-plasma technology onto a substrate made of 40CrNiMo structural steel with a sorbite structure and a hardness of HRC 28–30. Within each nitride layer, the composition of the components was close to equiatomic, and for the coating as a whole it was Ti : Al : N = 1 : 1 : 2 (at %). The structure of the coatings, the morphology of the friction tracks and the wear mechanisms were studied using high-resolution scanning electron microscopy. The mechanical characteristics of the coatings (hardness H and elastic modulus E) were determined using standard continuous indentation techniques. The tribological characteristics (friction coefficient μ and volume wear J) were determined using the ball-on-disk sliding friction test with a circular trajectory of the indenter ball. The analysis of the obtained experimental data made it possible to construct a dependence of the coating hardness on their elemental composition and showed that the mechanical characteristics and wear resistance of the coatings sprayed at a lower temperature of 300–350°C are consistently higher than those sprayed at 400–450°C. In addition, it was found that the highest wear values J were observed for the coatings with the smallest thickness. In order to analyze the effect of coating thickness δ on their wear resistance, a computational and analytical model for predicting coating wear during tribological tests was used. On its basis, diagrams of critical states of ion-plasma composite TiN/AlN coatings were constructed, which made it possible to calculate the critical value of coating thickness δ_min, at which the mechanism of coating wear during friction changes. With a relatively thin coating (δ < δ_min), located on a “softer” (plastic) substrate, during tribotesting, accelerated wear of the coating occurs by the abrasive-mechanical mechanism due to the deflection of the coating and its subsequent cracking, peeling, and chipping. With a relatively thick coating (δ ≥ δ_min), wear occurs by the abrasion mechanism, which, with high hardness of the coating, is characterized by its significant wear resistance and significantly extends the service life.

The aim of the work is to identify the most effective conditions and modes for the synthesis of Mo–S–Ti–C coatings on titanium alloy VT5, providing the best tribological characteristics. The coatings were applied by vacuum arc evaporation of cathodes on a modernized NNV-6.6-I1 installation. The cathodes were produced using self-propagating high-temperature synthesis. Assistance to the gas discharge plasma during coating application was provided by an autonomous plasma source with a heated cathode. In this case, the bias potential on the substrate, the deposition time, and the composition of the working gas environment, argon and/or a mixture of argon and nitrogen in a ratio of 1 : 1, were varied. It has been established that the use of assisting action of gas discharge plasma on deposited coatings provides a 2–3 times increase in their hardness. Using energy-dispersive X-ray spectroscopy, the presence of both sulfide-forming elements (Mo, S) and elements capable of forming solid carbides (Ti, C) was revealed in the evaporated cathodes and in the applied coatings. X-ray structural analysis confirmed the synthesis of compounds of the Mo₂S₃ and TiC type in both cathodes and coatings. In the most effective version of a three-layer coating using, along with argon, nitrogen in gas discharge plasma, the formation of a strengthening phase of TiN was also recorded. Tribological tests were carried out under friction conditions without lubricant. It was established that the most effective version of a three-layer coating with the addition of nitrogen in a gas discharge plasma, compared to the initial VT5 alloy, showed a decrease in the friction coefficient under a load on the counterbody of 1 N—by 2 times, under a load of 5 N—by 3 times; the wear rate in both cases decreased by an order of magnitude or more. Thus, the presented technological method ensures the formation of a gradient-layered coating architecture and appears promising for industrial application.

The study of the content of ferromagnetic wear particles in used motor oil allows for an assessment of the degree of wear of the engine’s friction parts. This work describes a new method for determining the fractional composition of the system of ferromagnetic wear particles in used motor oil, based on the sedimentation kinetics of particles in the gravitational field and the instrumental time of transverse proton nuclear magnetic resonance (NMR) relaxation ((T_{2}^{*})) of hydrocarbons in a polydisperse suspension. Unlike the traditional sedimentation analysis by continuous weighing, the proposed method employs continuous measurement of the NMR relaxation time (T_{2}^{*}). It is assumed that suspended particles increase the magnetic field inhomogeneity of the relaxometer magnet, and the instrumental spin–spin relaxation time is proportional to the mass of the sediment. An analytical expression for the particle size distribution and the most probable equivalent radius for the mathematical model of the sedimentation curve was obtained. Two physical models of iron particles of different sizes introduced into fresh motor oils were studied. It was shown that at the same iron concentration in the oil, smaller particles cause greater magnetic field inhomogeneity than larger particles. The kinetics of changes in (T_{2}^{*}) relaxation times during sedimentation were investigated. It was established that during sedimentation of ferromagnetic particles, the spin-lattice relaxation time T₁ and the spin-spin relaxation time T₂ remain unchanged. To obtain the distribution of ferromagnetic particles, all necessary transformations of the (T_{2}^{*})(t) data array were performed numerically. It was demonstrated that, unlike the unimodal distributions observed for model samples of fresh oils with iron particles, the used M-10G2CS oil after 420 h of operation exhibits a broad radius distribution ranging from 3 to 11 µm. The particle radius distributions in Shell Rimula 15W40 oils used for 250 and 500 h, as expected, are similar; however, the percentage content of fractions in the oil used for 250 hours is lower than that in the oil used for 500 hours. The nature of these distributions differs from that of the M-10G2CS oil (420 h). The applicability of the proposed method to highly dispersed systems is limited by the very slow sedimentation of nanosized particles in the gravitational field. The results in this work may be useful for dispersion analysis of any organic suspensions containing microsized ferromagnetic particles.

A common defect of springs is a decrease in their wear resistance due to changes in the mechanical properties of the wire along its length, particularly the yield strength, including under friction during operation of the spring. According to the springs stress-strain state presented mathematical model, the wire yield strength changes effect on springs wear resistance during contact hardening is investigated. The residual springs deformation dependence graph on the yield strength of its material for different wire diameters is constructed. Dispersion of the spring wire yield strength in the coil according to state standards 9389, carbon steel spring wire can be up to 200–250 MPa. It is established that in this case, the manufactured springs deformation dispersion will amount to 11.76% and exceed the permissible values. For first precision group springs, the permissible deviations for deformation dispersion are ±5%, for second precision group springs, ±10%. The wire change in the yield strength effect graph along the length on the dispersion of spring deformation for a load of 140F₃ (F₃ is spring compression force when coils come into contact) is constructed. Using the presented technique and taking into account the dispersion of spring deformation depending on the change in the wire along the length yield strength, including due to friction during operation, it is possible to significantly reduce the percentage of defects in the manufacturing and increase helical cylindrical compression springs wear resistance.

The aim of the work is to study the effect of sliding velocity on the evolution of the subsurface structure and tribo-oxidation in a high-speed steel coating reinforced with WC after friction on a steel counterbody without a lubricant. In this work, we studied the tribological behavior of electron-beam composite coatings obtained from a mixture of R6M5 powder steel and WC in contact with a counterbody made of ShH15 steel. It was found that the structure of the coatings is a matrix based on γ + α' iron, reinforced with skeletal structures of eutectic carbides. A simultaneous decrease in the friction coefficient and wear rate of the coatings with an increase in the sliding velocity from 0.8 to 3.6 m/s was obtained. This is due to the tribochemical formation of FeWO₄ and Fe₂WO₆ iron tungstates at sliding speeds of 2.4 and 3.6 m/s, which then allows the formation of a surface mechanically mixed layer, which, in addition to the said iron tungstates, includes fragments of carbides and metal particles of the coating matrix. Such a friction surface structure provides a solid lubrication effect and protects the underlying coating structures from destruction. The specificity of such an adaptation mechanism is that it is realized at relatively low sliding speeds, which corresponds to the maximum calculated flash temperature of about 290°C. The tribological adaptation mechanism discovered should contribute to the successful use of WC/tool steel electron-beam composite coatings in various industries.

The effect of co-deposited graphene oxide (GrO) modified with COOH groups on the tribological characteristics of electrolytic nickel–molybdenum coatings has been studied. The coatings were formed on the surface of polished high-carbon steel by electrodeposition from an aqueous electrolyte based on nickel sulfate (NiSO₄) and sodium molybdate (Na₂MoO₄) with dispersed graphene oxide. The coatings were obtained at current densities of 2.5 A/dm² and GrO concentrations from 0.05 to 0.2 g/L. Tribotechnical tests have shown that introduction of GrO at a concentration of 0.1 g/L makes for the formation of a coating with a uniform structure ensuring a minimum friction coefficient (0.38–0.45) and a wear track width (25–110 µm) under a load of 0.25–1.0 N. A dependency of tribological characteristics on the concentration of graphene particles in the working solution was revealed: at 0.1 g/L, a uniform distribution of GrO particles is achieved, which leads to a 30–40% reduction in the friction coefficient and a 40–55% decrease in wear track width compared to the base Ni–Mo coating. When the particle concentration exceeds 0.1 g/L, an increase in coating roughness is observed, which is likely caused by agglomeration and excessive inclusion of filler particles into the coating structure; all this results in the formation of a rougher and more heterogeneous surface, thereby degrading the tribological properties of the coating. The results confirm the promising use of GrO in the composition of electrolytic Ni–Mo coatings to reduce friction and increase wear resistance.