Journal of Friction and Wear最新文献

The study of the structure and tribotechnical characteristics of composite material based on polyacrylonitrile (PAN) carbon fabric and a matrix obtained by the vapor deposition method has been carried out. One of the samples of the investigated material was subjected to laser treatment, with local laser heating of the surface layer to 2800–3000°C. The other composite sample was heat treated at a temperature T > 2000°C. Tribotechnical tests were carried out and values of friction and wear coefficients were obtained in the pair with steel and ceramic counterbodies. In order to determine the peculiarities of friction and wear mechanisms of modified materials, the surface of composites after friction was investigated by scanning electron microscopy with X-ray spectral analysis. It was found that laser treatment significantly improves antifriction properties of carbon composite paired with a steel counterbody (friction coefficient reduction by two times, wear reduction by three times). It is revealed that such treatment significantly changes the nature of the third body film (TB) formed on the friction surface of composites paired with steel. No elements of the counterbody material are detected in the composition of the film, which indicates its minimal wear during the friction process. The TB film itself becomes thicker and denser, completely covering the surface of the composite. This allows it to exhibit solid lubricant and anti-wear properties to a greater extent, improving the tribological characteristics of the composite.

The results of studies on the wear resistance of machine parts made of aluminum alloys with insulated layers obtained by activating surface layers (SLs) are considered. It is shown that, in relation to aluminum alloys, traditional ion nitriding technologies are ineffective due to the low rate of nitrogen diffusion and the heterogeneous structure of the nitrided layer (NL). The results of a fourfold increase in the intensity of diffusion processes of ion nitriding during activation of the surface layer of an aluminum alloy by methods of surface plastic deformation and high-energy ion implantation compared with traditional ion nitriding are presented. It is shown that when preparing the surface of an aluminum alloy by the method of high-energy ion implantation, the wear resistance of the nitrided layer is provided, exceeding by more than three times the wear resistance of the nitrided layer obtained during surface preparation by the method of surface plastic deformation. A new ion nitriding technology has been proposed, which makes it possible to increase the productivity of the nitriding process and the wear resistance of the AC by eliminating the oxide film by ion etching in vacuum. It is shown that the use of the method of high-energy ion implantation at an ion energy of about 25 keV ensures, due to the occurrence of a long-range effect, the formation of aluminum alloy parts in the surface layer at a depth commensurate with the thickness of the nitrided layer of radiation defects of the crystal structure, which significantly intensify nitrogen diffusion, as well as block grain boundaries inhibiting diffusion processes in them.

Using electrospark alloying, Cr–Fe–Al₂O₃ coatings are obtained on steel 35 in a mixture of steel granules with chromium and aluminum oxide powders. The structure of the coatings is studied using X-ray diffraction analysis, scanning electron microscopy, and X-ray spectral microanalysis. The heat resistance of the coatings was studied for 100 h at a temperature of 700°C in air. The study of the mechanical properties of the coatings includes testing for microhardness under a load of 0.5 N and wear in the dry friction mode under a load of 25 N. According to X-ray diffraction analysis, the coating composition is dominated by ferrochrome and a small amount of aluminum oxide. According to EDS analysis, the element distribution in the coating is uniform throughout the coating thickness with a chromium concentration of about 60 at %, iron, 30 at %, and aluminum, 3.4 at %. The results indicate a uniform distribution of fine particles of aluminum oxide in the volume of the deposited layer. It has been shown that the metal powder participates four times more actively in the formation of the coating compared to the granules. The heat resistance test shows that with addition of Cr–Fe–Al₂O₃ powder in the anode mixture, the average rate of high-temperature weight gain of the samples increases. In general, the use of Cr–Fe–Al₂O₃ coatings increases the heat resistance of steel 35 from 2.4 to 4 times. The average values of the friction coefficient of coatings range from 0.76 to 0.83, with a minimum for the sample deposited using a minimal addition of Al₂O₃. The wear of the samples decreases monotonically from 3.3 × 10^–6 to 1.8 × 10^–6 mm³/(N m) with a decrease in the concentration of aluminum oxide in the anode mixture. In general, the application of Cr–Fe–Al₂O₃ coatings using the proposed method makes it possible to increase the wear resistance of the steel 35 surface from 11 to 20 times.

A technique and an algorithm of digital surface image processing are proposed to increase the validity of real-time detection of small size defects. The algorithm is implemented in the MATLAB programming environment. The technique is based on segmentation of the high-frequency component of surface texture because small size defects are especially pronounced in this component. The high-frequency component, in particular roughness, is extracted by means of wavelet transform for frequency components separation and homomorphic filtration for compensation of low-frequency distortion caused by nonuniform illumination of test surface. Segmentation of the high-frequency texture component consists in formation of a binary image using the texture descriptors derived from the gray-level co-occurrence matrix as the segmentation threshold. The proposed technique and algorithm are approved in applications to defect detection for a simulated surface, for real ground surface of hardened steel, and for surfaces of carbon fiber reinforced plastic composite. Extraction efficiency of the high-frequency component of surface texture is shown. It is found that texture descriptors, “contrast’ and “energy,” can be applied as segmentation thresholds for defect extraction/determination on the ground (anisotropic) surface while segmentation of an image of a plastic composite (isotropic) surface is effective just with “energy” as a threshold. The proposed technique can be applied for simultaneously real-time monitoring the surface texture and detecting the small size defect in machine vision systems during production and operation of tribosystems.

This article describes the experimental bench simulating the operation of thrust bearings of the main circulation pump (MCP) of powerful power plants. The coolant moves in them at high speeds (5–10 m/s), at high pressure (up to 150 × 10⁵ Pa) and temperatures up to 300°C. This entails the requirements for increased reliability of this unit. The bench was adapted for testing both when the bearing is lubricated with oil and when lubricated with water. The substitution of mineral oils with water became possible thanks to a comprehensive improvement of the bearing through the introduction of new antifriction materials and design solutions. The bench was also equipped with measuring systems for recording the moment of resistance to the rotation of the disk, the rotational speed of the disk, the angular velocity of the disk, and the temperature field near the working surfaces of the thrust bearings. The startup–rundown operating regime was programmed with a special software function. As a result of the studies, it was shown that simulating the main rundown stage on a test bench when a thrust bearing is operating in a water-filled volume cannot provide a comprehensive assessment of the performance of the main thrust bearing, since under operating conditions the lubrication process may be disrupted due to partial drainage of the bearing, leading to lubrication starvation, a sharp deterioration in heat dissipation, and damage. These phenomena must be carefully studied on real objects.

Based on the proposed loading model of a sliding bearing, the dependence of the load-bearing capacity of reinforced metal fluoroplastic sliding bearings on their geometric characteristics and force factors was studied using the finite element method. A calculation of stresses and deformations in the most pliable antifriction layer was carried out. It is shown that the distribution of stresses and deformations in the bearing is extremely uniform and depends on the thickness of the antifriction layer and the height of the bearing. Criteria for assessing the performance of sliding bearings under load were introduced and based on these criteria the results were compared with experimental data. The agreement between calculated and experimental data allows us to use the resulting methodology to determine the load-bearing capacity of slide bearings. The solutions make it possible to move from the experimental method of determining the load-bearing capacity of metal fluoroplastic sliding bearings to the calculated one and to design bearings with predetermined strength characteristics. This will help specialists designing bearing units improve the quality and speed of their development.

It is shown that friction fracture surfaces can be self-affine with a local fractal dimension. However, the intersection of such a self-affine surface with a plane gives similar contour lines, which are undoubtedly self-similar. The above considerations regarding the fractal properties of fracture surfaces give reason to believe that a rough surface in contact with metallic bodies in the process of friction is also self-similar. This article presents the fractal dimensions of the transient contact regimes (from elastic to elastoplastic and from elastoplastic to plastic contact) for self-affinity curves, which are the curves of the reference surface at various combinations of material parameters: Poisson’s ratio, hardness, and modulus of elasticity. In the calculations, the Minkowski dimension, calculated by the cellular method, was taken as the fractal dimension of curved reference surfaces. This method, based on the consideration of contact interaction, formed the basis of the method for calculating the contact characteristics of bodies, taking into account their macroshape and the roughness of friction surfaces. The results of the study are of great importance for the development of engineering methods for calculating homogeneous and inhomogeneous rough bodies.

This paper presents the results of tests of EPAN coatings, a composite material based on carbon–carbon fibers. It uses fine molybdenum disulfide as the main lubricant and for binders, phenol, peroxide, and silicone resins. The tests were carried out on microarc oxidation (MAO) coatings. For comparison, the tribological characteristics of EPAN under friction on steels, as well as molybdenum disulfide composites are given. The friction coefficients of EPAN coatings on MAO coatings according to the “shaft–bushing” scheme do not exceed 0.05 at pressures of 10–20 kg/cm² and shaft rotation speeds from 130 to 600 rpm. The advantage of such combinations of materials is the use of a light alloy, aluminum with MAO coating, for the counterbody to the EPAN coatings, which is important for space products. The creation and testing of solid lubricating coatings for modern space technology is a task of extreme importance, because in many developments of space products, low-temperature plastic lubricants continue to be used, which are operable up to subzero temperatures of –90 to –110°C. Such solutions require the use of thermal insulation and heating for mobile interfaces and friction units of machines, mechanisms, and devices. The result is a serious complication of structures and an increase in their weight. The tests of EPAN coatings on MAO coatings carried out in the work open new possibilities in the combination of materials for space technology. Having a coefficient of friction of 0.05 and high wear resistance, they allow you to create movable joints, first of all, sliding bearings, for operation on Earth sensing satellites, as well as mechanisms on the Moon.

The evaluation of the corrosion wear rate was carried out using the Norsok Standart M-506 method for oilfield production tubing in Belarus. The method is based on a model that takes into account the speed of the gas-liquid flow, its pH, the volumetric flow rate of water, oil, gas, pressure, temperature, immersion depth, pH, density and viscosity of these media, and diameter and wall thickness of tubing. A feature of the model is the consideration of the friction of the gas-liquid flow on the walls of the tubing and the resulting shear stresses near them, which allows taking into account the corrosion-mechanical component of the metal degradation process of the tubing. The characteristics of well media and operating conditions of equipment in fields are given. Empirical coefficients of the considered model for typical conditions of Belarusian oil fields have been determined and a predictive calculation of the corrosion rate of 32Mn1A tube steel strength group N80 (Q) of the API Specification 5CT has been carried out. Data on actual values of corrosion wear of tubing from more than 100 production wells have been collected. The results indicate a high convergence of calculated and actual data. The adapted Norsok Standart M-506 method of predicting corrosion wear is recommended for use at oil fields in Belarus. It is shown how the proposed approach can be extended to other oil-bearing regions.

The tribological properties of carbon–carbon antifriction composite materials reinforced with carbon fabric based on polyacrylonitrile and viscose raw materials have been studied. Tribological tests were carried out according to the ring–disc scheme paired with silicon carbide ceramics under dry friction conditions with different orientations of the composite fabric layers relative to the friction surface in the temperature range of 80–100°C. Dependences of the friction coefficient and wear rate on the fabric orientation relative to friction surface, structure of the composite, and properties of its structural components were obtained at a fixed load and sliding speed. The surface of composites was analyzed after tribological tests using scanning electron microscopy and optical profilometry. The composites friction and wear mechanisms for different contact configurations and different material properties have been revealed. The characteristic features of composite individual structural (fibers, fiber bundles, layers of reinforcing fabric) frictional destruction have been determined. It has been established that the film of wear products formed on the friction surface has a decisive influence on the tribological characteristics of the studied materials. Combinations of the fabric base of the composite, its orientation relative to the friction surface, and the heat treatment mode of the material were determined, which simultaneously provide increased wear resistance and reduced friction in tandem with a ceramic counterbody.