Journal of Friction and Wear最新文献

Friction and wear of polyoxymethylene upon friction against polyoxymethylene and polyetheretherketone have been analyzed. It is shown that wear exponentially increases upon growth of contact pressure and sliding velocity in the homogeneous friction pair polyoxymethylene–polyoxymethylene. In the heterogeneous pair polyetheretherketone–polyoxymethylene the wear of POM is small and exhibits no registered dependence on sliding velocity and contact pressure. Mass-spectrometric analysis shows that the macromolecular decomposition products are not detected for polyetheretherketone–polyoxymethylene pair. However, for thermodynamically compatible polyoxymethylene–polyoxymethylene pair their formation, accompanied by the growth of friction force, is detected already at the levels of friction power as low as 10^–2 MPa m/s. These differences have been interpreted to result from interpenetration of polyoxymethylene macromolecules across the interface and their rupture in the shear field in homogeneous polyoxymethylene–polyoxymethylene friction pair and its absence in polyetheretherketone–polyoxymethylene pair. Thermally activated interpenetration of macromolecules for polyoxymethylene–polyoxymethylene pair and its absence in polyetheretherketone–polyoxymethylene pair has been visualized by means of molecular dynamics simulations. The experimental approach and the results of its application will be useful in detailed studies of molecular level friction mechanisms of friction and wear of industrially used polymers and their composites.

The study compared properties of carbon–carbon composites for manufacturing aircraft brakes. Composites based on various graphitized and carbonized fibers, coal, tar pitch, and pyrocarbon matrices were considered. Friction tests were carried out on full-size brake discs (three-disk stand) and on model samples (UTM-2168 testing machine). A significant wear increase of composites based on a pyrocarbon matrix was found during taxi braking in the temperature range of 50–250°C. Wear of composites based on a coal tar pitch matrix did not depend on the temperature of the friction surface. It was found, that the “third body” of composites based on pyrocarbon has a coarse rough structure with distinct individual abrasive particles; its hardness is more than twice as high as the hardness of the third body of composites based on pitch matrix. The size distribution of pores for composites based on different matrices is given, the difference in the quantity and size of structural defects is illustrated. The variation in wear of materials during taxi braking is explained. The increase of degree of anisotropy of the pitch matrix, provided the decrease of wear of the material. The wear was measured during taxi braking of specimens with a hybrid matrix having a different ratio of coal tar pitch and pyrocarbon components. Carbon–carbon composites containing 45% or more of the pitch component in matrix have stable reduced wear during taxi braking, regardless of the reinforcement scheme. The possibility of reducing wear during taxi braking of composites on pyrocompacted matrices by modifying the matrix with pitch is shown.

The paper considers wear-free friction of ShKh-15 (ShKh) steel balls on the surface of quartz glass (QG) and borosilicate glass (BG) vessels in organic liquids and water. It is shown that it is impossible to accurately predict which material will wear out faster: hard or soft, ball or substrate. The highest correlation between the wear of coupling friction surfaces is found for balls and the total wear of working bodies (r ≈ 1). In the group of glass balls, the balls wear out more often (19 out of 21 tests) than in the group of steel balls (5 out of 9 tests). Wearless friction is more often observed in coupled pairs BG/ShKh (5 cases) than in pairs QG/ShKh (1 case). Coupling surfaces containing only one terminal SiOH group do not provide wear-free boundary friction. The usefulness of the work is in the fact that the results of studies of wear-free friction obtained for the ShKh/H₂O pair can find practical application in the creation of bearings and large human joints.

The article is devoted to an experimental study of the influence of wear-resistant coatings ZrN, TiN + ZrN, (Ti–Zr)N, ZrN–(Ti–Zr)N–TiN, and TiN, deposited on T15K6 hard alloy inserts, on the tribological and deformation characteristics of the process of turning 45 and 12Kh18N10Т steel workpieces, and subsequent comparison of the calculated values of the maximum temperatures of the rake face of the lathe cutter. When processing 45 steel, a significant reduction in contact and average temperature in the cutting zone is ensured by a combination of tribological and deformation indicators when using TiN + ZrN and ZrN + (Ti,Zr)N + TiN compositions. When turning 12Kh18N10T stainless steel, the presence of coatings on carbide inserts had a lesser effect on the course of deformation processes. The main effect of modifying the working surfaces of the tool is to change the thickness of the zone of secondary plastic deformations and to reduce the length of contact between the chips and the rake face. In this case, the greatest effect in reducing surface temperatures due to the influence on the complex of tribostrain indicators and enhancing the thermodissipative capabilities of the contact zone is demonstrated by ZrN and ZrN + (Ti,Zr)N + TiN coatings. Based on the results of full-scale experiments and digital modeling using the obtained experimental data, it was established that the temperature distributions in the area of tribocoupling of chips with the surface of a hard alloy in the presence of a multilayer coating on it are associated with the wear of metal-cutting tools, which makes it possible to evaluate the impact of wear-resistant coatings through changes in the temperature regime in the contact zone. Such an influence of surface modification on a set of tribostrain indicators, which also determine the nature of the distribution of contact temperatures, should be taken into account when developing new compositions and structures of wear-resistant coatings along with their physical and mechanical properties at the microlevel.

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.

The structure, microhardness, and tribological properties of coatings obtained in the process of surfacing of powder mixtures by an electron beam ejected into an air atmosphere are studied. For surfacing, we used a powder mixture containing amorphous boron and a wetting component, the role of which was played by Fe, Cr and Ni powder particles. The function of protecting the molten material from the air atmosphere was performed by MgF₂ flux. The thickness of the formed coatings reached 2.3–2.8 mm. The maximum level of microhardness of coatings reaches ~1500 HV. The main mechanism of hardening of such is due to the presence in the material of up to 90% (volume) particles of the hardening phase. It is shown that chromium borides Cr₂B and (Fe,Cr)₂B play the role of a hardening phase in the γ-phase (Ni, Fe solid solution). Chromium is contained in the alloying powder mixture and the base material. During the cladding process, chromium diffuses and forms borides. This process occurs due to the greater affinity of chromium for boron than nickel and iron. It has been established that chromium containing coatings have maximum wear resistance under various abrasive conditions. The wear resistance of coatings increased by 5 times compared to stainless steel 12Х18Н9T under friction with fixed abrasive particles. The wear resistance of hardened layers under conditions of gas and hydroabrasive action at low angles of attack (15°, 20°) increased by 6 and 2 times, respectively.