The influence of technological parameters of laser processing on tribotechnical characteristics of steel 45 has been investigated, allowing to develop recommendations for obtaining maximum wear resistance. The influence of laser processing modes (pump current I, pulse duration τ) on the values of energy in the pulse E transferred to the surface to be processed has been evaluated. Changing the current strength in the range of 60—120 A and pulse time from 5 to 25 ms allowed to obtain the change of energy in the pulse in the range from 0.3 J to 4.1 J. It was found that tribotechnical properties of the surface treated with the same energy but different modes of exposure differ. The wear resistance of the sample was estimated by the width of the friction track. It was found that the influence of pulse duration on tribotechnical characteristics is extreme: at pumping current of 60 A the minimum friction coefficient and maximum wear resistance were obtained at pulse duration of 20 ms. Increase of pulse duration more than 20 ms leads to lamellar fragments peeling off on the surface and deterioration of tribotechnical parameters.

An experimental method for determining the friction coefficient in metal forming processes using a universal friction machine has been developed. This method allows to compare the lubricating ability of different emulsions in an efficient way. The experiments were carried out on the universal friction machine MMW-1A. Samples of cold-rolled strip 0,09 mm (steel TS-435, analogue 08ps) and a sample of rolls material of cold rolling mill of especially thin sheets, type RCM-1250 (steel 60X2HFА) 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 in S = 4 mm and more was confirmed. It has been found out 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-second 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 obtained 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.

The article is devoted to the evaluation of tribological and thermoelectric characteristics of the process of turning a hybrid part made of 09G2S steel, the surface of which contains a weld, with plates of T15K6 hard alloy at different cutting speeds. In this paper, the rake face of the lathe cutter, which contacts at the stage of cutting into the weld with chips of different composition, is presented as two parallel functioning heavily loaded tribosystems with variable geometric parameters of contact, which differ in tribodeformation indicators and surface temperature. The composition and geometric characteristics of fragments for each processed material were determined using the graphic model of the removed non-uniform allowance. Based on the obtained dimensions of the hybrid allowance elements, the maximum contact temperatures were calculated for each tribosystem at different cutting speeds. The processing modes were determined that ensure a minimum difference in surface temperatures on different sections of the rake face of the cutting inserts, which increases the thermoelectric stability of the turning process. In the course of full-scale experiments it was established that the turning modes, in which, according to the calculated data, more uniform heating of the front face occurs, are also characterized by minimal fluctuations of the relative thermoEMF at the stage of cutting the plate into the weld. Exceeding these turning speeds in the studied cutting system leads to an in-crease in negative thermoelectric effects, contributing to the intensification of the wear process of the cutting plates. The presented research results, in combination with other technological factors for choosing the processing modes, can become an additional tool for assigning permissible turning speeds for welded sections on hybrid parts.

Tribotechnical investigations of steels of the grades 5ХНМ, 11Х4В2МФ3С2 and 95Х6М3Ф3СТ were conducted under conditions of dry sliding friction in pairs with cylindrical indenters fabricated from hard alloy ТТ10К8Б at a load of 40 MPa. The test scheme is 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 of the samples was 10 hours. The amount linear wear of the friction pair elements was used as a criterion of resistance during sliding friction. Minimal wear under conditions of dry sliding friction paired with a ТТ10К8Б hard alloy indenter was recorded when testing samples of 11Х4В2МФ3С2 high carbon tool steel after quenching at 1060 °C and triple tempering at 525 °C. The amount of total linear wear in the friction pair “steel 11Х4В2МФ3С2 — hard alloy ТТ10К8Б” is 4 times less than that of the pair “steel 5ХНМ — hard alloy ТТ10К8Б”.

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.

This work is dedicated to the study of tribological behavior of composite materials obtained by friction stir processing (FSP) from aluminum-magnesium alloy AA5056 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 con-tent, 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 was 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 compounds (IMCs) particles of the Al₆Fe and Al₁₃Fe₄ types 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 wearresistant antifriction coating.

The cavitation wear tests of six polymers were carried out. There were polymers of different classes chosen: Teflon, high-density polyethylene, plexiglass, polyamide, polyurethane, epoxy compound K-153. The cavitation attack was executed in mild fresh water, the latter was kept at temperature of 20 ± 3 ℃. The test apparatus was an ultrasonic magnetostrictive device, the frequency and the amplitude of horn butt-end oscillations being equal to about 22 kHz and 28 μm respectively. The polymers samples were in the shape of cylinders. The test surfaces were the sample flat ends, which were ground and polished. The Shore hardness, sound speed and density of the polymers were measured before putting them to test. During the experiments the mass loss and the roughness of the test surfaces were measured and dependences of the mass loss and arithmetical mean deviation of the assessed profile on cavitation attack duration were built. The wear of all the polymers tested occurs with incubation period. In order to avoid the rough error in the determination of the incubation period the latter was evaluated by profilometry. There was the tough-brittle transition indicated on the dependences of the incubation period and wear rate on the cavitation attack duration, and in the tough failure zone the influence of the hardness on the wear resistance is the opposite to that in the brittle failure zone. In both the tough failure zone and the brittle failure zone the cavitation wear resistance goes down as the acoustic impedance increases, however the polymers suffering brittle damage in cavitation attack and ones suffering tough damage form the separate dependences of wear resistance on the acoustic impedance. The acoustic impedance has strong influence on the wear resistance of polymers in the brittle failure zone and weak influence in the tough failure zone. To secure the highest cavitation resistance it is necessary to choose the polymers having the Shore hardness as nearly as possible to the tough-brittle transition, that is the Shore hardness has to be in value from 65 to 70.

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 reciprocating scheme ASTM G133 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 initial state; mixture with Al₂O₃ nanoparticles; emulsion (20 % canola oil + 80 % water). It is established that in conditions of contact “abrasive material—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 in contact. At 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 “abrasive—metal”. Dynamics and character of wear of 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.

The effect of borating on the structure and tribological characteristics of VKS-5, Kh12MF, 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 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 borated 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 borating in a standard melt and in a melt with the addition of La₂O₃; ≈ 0.20 — for steel after borating with the addition of Sc₂O₃; ≈ 0.14 — for steel borated 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. Borating 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. Borating forms wear-resistant diffusion layers on the surface of steel 40Kh. The best results in the combination of two tribotechnical characteristics (wear intensity and friction coefficient) for the friction pair steel 40Kh — steel SS440 were obtained under conditions when the steel was borated in a melt of standard composition.

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 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 promotes 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, leading 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, likely caused by agglomeration and excessive inclusion of filler particles in the coating structure, which results in the formation of a rougher and more heterogeneous surface, thereby degrading the tribological properties of the coating. The obtained results confirm the promising use of GrO in the composition of electrolytic Ni-Mo coatings to reduce friction and increase wear resistance.