Journal of Friction and Wear最新文献

A complex approach for evaluating the functional characteristics of coolants for grinding hard-to-machine materials is proposed, which is realized by means of experimental modeling of damage to the machined material and a single roughness of the grinding wheel during simulated cutting with gripping. Selection of lubricating medium for abrasive machining is carried out on the basis of establishment of critical processes in the cutting zone with the help of tribological parameters and accompanying signals of acoustic emission (AE) obtained as a result of tests on the ASTM G133 reciprocating scheme of two pairs of friction: abrasive material–metal and metal–metal. The study was carried out for environmentally oriented lubricating media using canola oil: in the initial state; mixture with Al₂O₃ nanoparticles; emulsion (20% canola oil + 80% water). It is established that in conditions of contact between abrasive material and metal application of emulsion provides reduction of adhesive adhesion of the contacted surfaces, the minimum coefficient of friction in tests, and the lowest level of wear of the contacted pair. Considering metal–metal contact interaction, the use of canola oil composition with Al₂O₃ nanoparticles will be the most effective here, due to high wear resistance and low plastic deformation during contact. During tribological tests of the investigated friction pairs, it is established that the maximum influence on the AE signal value is exerted by the level of adhesion processes at the contact interaction of abrasive–metal. The dynamics and character of wear of the friction pair metal–metal has its own features, which is reflected in the behavior of the accompanying AE signal, the fact that the value of the integral AE estimation does not directly correlate with the results of wear of the contact pair and strongly depends on the composition of the lubricating medium.

This work is dedicated to the study of tribological behavior of composite materials obtained by friction stir processing (FSP) from AA5056 aluminum–magnesium alloy with addition of iron under dry sliding friction. For the tests, four different types of samples were obtained by FSP, differing in their iron powder content, namely 0, 5, 10, and 15 vol %. For each type of composite, four passes of FSP were performed to achieve a uniform distribution of the iron powder throughout the stir zone. Sliding tests were conducted using the pin-on-disc method against a counter-body made of stainless steel containing 12–14% chromium (AISI 420). Increasing the Fe powder content leads to a decrease in the average coefficient of friction by approximately 10–15%, as well as a reduction in wear by approximately 20%. The study of worn surfaces showed that with an increase in the amount of iron powder added during FSP, the wear mechanism changes from adhesive to abrasive. Homogeneous distribution of intermetallic compound (IMC) particles of Al₆Fe and Al₁₃Fe₄ in-situ synthesized during FSP made it possible to increase the wear resistance of the composites compared to the base alloy without iron additives. A mechanically mixed layer consisting of a deformed matrix mixed with fragmented and oxidized IMCs was formed on the worn surfaces of all the studied composites and served as protection against adhesive wear and performed the function of a wear-resistant antifriction coating.

The effect of boriding on the structure and tribological characteristics of VKS-5, Kh12MF, and 40Kh steels was studied. The samples were processed in a melt based on sodium tetraborate and boron carbide with the addition of lanthanum, yttrium, and scandium oxides in an amount of 5%. It was shown that this type of chemical-thermal treatment (CTT) is an effective means of increasing the tribological efficiency of steel joints for operating conditions without a lubricant. When testing the friction pair of VKS-5 steel–SS440 steel, the maximum decrease in the friction coefficient is observed if the steel is borided in the melt with the addition of Y₂O₃, the smallest, with the addition of La₂O₃. The values of the friction coefficient in the steady-state mode are: ≈0.45 for the original (not subjected to CTT) surface, steel after boriding in a standard melt, and in a melt with the addition of La₂O₃; ≈0.20 for steel after boriding with the addition of Sc₂O₃; and ≈0.14 for steel borided in a melt with the addition of Y₂O₃. The wear of VKS-5 steel decreases by ≈6.7 times after treatment in a standard melt, by 5.0, 4.2 and 3.6 times, respectively, in a melt with the addition of La₂O₃, Sc₂O₃, and Y₂O₃. Boriding of Kh12MF steel in a standard melt reduces the friction coefficient by 1.7 times, and wear by 1.8 times compared to steel without CTT. The average value of the friction coefficient decreases by 2.9, 2.7, and 2 times in melts with the addition of La₂O₃, Y₂O₃, and Sc₂O₃, respectively; the wear intensity in the melt with La₂O₃ does not increase significantly, with Y₂O₃, it decreases by 1.6 times, and with the addition of Sc₂O₃, it decreases by 1.3 times. Boriding forms wear-resistant diffusion layers on the surface of 40Kh steel. The best results in the combination of two tribotechnical characteristics (wear intensity and friction coefficient) for the friction pair 40Kh steel—SS440 steel were obtained under conditions when the steel was borided in a melt of standard composition.

The tribological and thermoelectric characteristics of the turning process of a hybrid part made of 09G2S steel, the surface of which contains a weld, have been estimated using T15K6 hard alloy plates at various cutting speeds. In the used model, the rake face of the lathe cutter, which contacts chips of different composition at the stage of cutting into the weld, has been presented as two parallel heavily loaded tribosystems with variable geometric parameters of contact, which differ in tribostrain indicators and surface temperature. Based on the graphical model of the removed non-uniform allowance, its composition and geometric characteristics of fragments for each processed material have been established. Based on the obtained dimensions of the hybrid allowance elements, the maximal contact temperatures have been calculated for each tribosystem at various cutting speeds. The cutting speed that ensures a minimal difference in surface temperatures in different areas of the front face of the plates has been determined. It has been established that the turning speed, at which, according to the calculated data, more uniform heating of the front face occurs, is characterized by a decrease in fluctuations of the thermo-EMF arising at the stage of cutting the plate into the weld. Exceeding this speed leads to an increase in the negative influence of thermoelectric effects, which contribute to the intensification of wear of cutting plates. The presented research results, in combination with other technological factors for selecting processing modes, can be used to assign permissible turning speeds for welded areas on hybrid parts.

An experimental method for determining the friction coefficient in metal forming processes using a universal friction machine has been developed. This method allows one to compare the lubricating ability of different emulsions in an efficient way. The experiments were carried out on a MMW-1A universal friction machine. Samples of 0.09-mm cold-rolled strips (TS-435 steel, analog 08ps) and a sample of roll material of cold rolling mill of especially thin sheets, type RCM-1250 (60X2HFА steel) were selected for research. Besides optimization of the methodology of such experiments, the character of the influence of coolant pH on the friction coefficient was determined. Friction conditions–semi-liquid friction. The expediency of using annular samples of the pair with thickness S = 4 mm and more was confirmed. It has been found that the time of carrying out the experiment should be commensurable with the duration of the investigated process of metal pressure treatment. For cold thin sheet rolling, it is most appropriate to conduct a series of 4–5-s experiments. The processing of experimental data has shown that the increase in pH values of coolant leads to an increase in the friction coefficient. The results can be useful for calculation of energy and power parameters of cold rolling of strips, for calculation of rolling routes, and optimization of applied coolants in processes of cold deformation of metals.

Tribological studies of 5KhNM, 11Kh4V2MF3S2, and 95Kh6M3F3ST steels have been performed under dry sliding friction conditions in pairs of a steel disk–TT10K8B hard alloy pin at a pressure of 40 MPa. The test scheme has been based on the reciprocating movement of a steel sample relative to a carbide counterbody at a speed of 0.1 m/s. The test time for each sample was 10 h. The value of linear wear of friction pair elements has been used as a resistance criterion in the process of sliding friction. Minimal wear under dry sliding friction conditions in a pair with a TT10K8B hard alloy indenter has been recorded when testing samples of 11Kh4V2MF3S2 high-carbon tool steel after hardening from 1060°C and three-fold tempering at 525°C. The value of the total linear wear in the friction pair 11Kh4V2MF3S2 steel–TT10K8B hard alloy is four times less compared to that of the pair 5KhNM steel–TT10K8B hard alloy.

Cavitation wear tests on six polymers belonging to different classes: polytetrafluoroethylene, low-pressure polyethylene; polymethyl methacrylate, block polyamide (caprolon), polyurethane, and epoxy compound K-153 have been performed. The experiments on an ultrasonic magnetostrictive vibrator in soft fresh water at a temperature of 20 ± 3°C have been carried out. The frequency and amplitude of oscillations of the vibrator concentrator end were 22 kHz and 28 μm, respectively. The samples had a cylindrical shape, the end surfaces of which, subject to testing, were ground and polished using the same technology for all polymers. Before the tests, the density, sound velocity in polymers, and Shore hardness (type D) have been measured. During the tests, the mass loss of the samples and the surface roughness have been measured, and the dependence of the mass loss and the arithmetic mean deviation of the surface profile on the duration of the cavitation effect has been plotted. The wear of all polymers occurred with an incubation period. A viscous–brittle transition has been observed in the dependences of the incubation period duration and the wear rate on the Shore hardness, while in the viscous fracture region, the effect of the polymer hardness on their cavitation wear resistance is opposite to that in the brittle fracture region. It has been found that both in the viscous and brittle fracture regions, the cavitation wear resistance of the polymer decreases with increasing acoustic resistance. It has been concluded that in order to ensure the greatest cavitation wear resistance, it is necessary to select polymers with a hardness value that would ensure viscous–brittle fracture of the polymer at Shore hardness in the range of 65–70.

Friction tests were performed on a disc made of oil- and gasoline-resistant rubber during reciprocating sliding on a polished steel surface with lubrication. The tests were carried out at room temperature for roughness values of 0.63 and 1.27 microns, lubrication with water, MDPN-C oil, and castor oil, and a pressure range of 0.5–20 MPa. Cyclic programs with stepwise varying constant pressure levels and pressure changes proportional to the displacement in the friction pair were considered. The dependence of the coefficient of friction on pressure in the range of 0.5–20 MPa for both oils is well approximated by the inverse power law, differing in this range by a factor of 10–20. The coefficient of friction when lubricated with castor oil is 2–5 times lower (depending on pressure) compared to its value when lubricated with MDPN-C oil, and the latter is 1.5–8 times lower when lubricated with water. In a test with a constant pressure level, the coefficient of friction does not stabilize, and its value increases with roughness for castor oil and MDPN-C oil (at low pressures), decreases for water and MDPN-C oil (at high pressures), demonstrating dependence on the wettability of the rubber with grease and the drainage properties of the counterbody surface. In the proportional pressure change test, the friction coefficient is reached, stabilizes, and increases with roughness. The test data is approximated for use in numerical calculations in the design of friction units.

Wear mechanisms of organic composite materials with low content of metallic elements for braking systems of medium and heavy loading have been studied. The tests were carried out on the “finger–disc” scheme on the MMW-1 friction machine. The thermal effect during friction was modelled by the finite element method with focus on heat distribution on the surface. It was found that the sliding speed has the greatest influence on the wear intensity and constitutes 52.24%. A decrease in the friction coefficient at temperatures above 490°C was observed. Materials with high Cu–C content (20 wt %) showed less wear and lower friction coefficients due to graphite, while materials with low Cu–C content (5 wt %) were subjected to more pronounced abrasive wear due to overheating. Composites with 25 wt % binder also showed signs of abrasion, while at 35 wt % binder content the surface was characterized by a more uniform topography. However, the increased binder content led to local thermal failure, which manifested itself in the form of cracks and surface damage. The practical significance lies in the possibility of optimization of materials to improve their wear resistance at high temperatures and loads.

Ti–Mo–Si coatings for protection of Ti–6Al–4V titanium alloy from wear and high-temperature oxidation applied by electrospark alloying are studied. To form the Ti–Mo–Si coating, a non-localized electrode consisting of titanium granules with the addition of silicon and molybdenum powders is used. A Dron-7 X-ray diffractometer in CuK_α radiation is used to study the phase composition of the coatings. According to the X-ray phase analysis data, the phases of αTi, Mo, Ti₅Si₃, and TiSi₂ are found in the coating composition. The average thickness of the prepared coatings is in the range from 31.70 to 40.97 μm. According to the energy dispersive analysis, titanium predominated in the coating composition, the concentration of molybdenum reached 18 at %, and silicon, 9 at %. It is shown that silicon particles participated disproportionately less in the formation of the coating compared to molybdenum particles. Heat resistance testing shows that the use of the developed Ti–Mo–Si coatings allows increasing the heat resistance of the Ti–6Al–4V titanium alloy at a temperature of 900°C by up to 5.7 times. The microhardness of the Ti–Mo–Si coating surface is in the range from 5.81 to 9.88 GPa. It is found that with an increase in the silicon to molybdenum ratio in the non-localized electrode, the average values of the friction coefficient of the coatings in the dry sliding mode monotonically increase from 0.81 to 0.86. The use of Ti–Mo–Si coatings allows reducing the surface wear of titanium alloy products by up to 19 times. The coating with the highest silicon content demonstrates the highest hardness, wear resistance, and heat resistance.