The influence of the type of motion friction (sliding/rolling) on the behaviour of anti-wear additives of lithium grease has been investigated. The tests of plastic lubricant on wear under conditions of sliding friction on a four-ball friction machine (FBFM-1) and as a part of a rolling bearing have been carried out. The multidirectional influence of additives on tribological properties of plastic lubricants is shown. Introduction of detonation nanodiamonds into lithium PL in concentration of 0.3 % by mass in conditions of rolling friction leads to decrease of friction coefficient in relation to basic PSM in 2 times and increase of relative life. In conditions of sliding friction the anti-wear properties are improved by 1.7—1.9 times. Addition of tricresyl ether of orthophosphoric acid (TKF) to lithium PL in rolling friction conditions leads to increase of friction coefficient in 3,65 times and decrease of relative life, and in sliding friction conditions increases anti-wear properties in 1,9 times. The results of researches allow to pick up optimum composition of additives depending on working conditions of a friction unit.

Ti-Mo-Si coatings were prepared to protect of the titanium alloy Ti-6Al-4V from wear and high-temperature oxidation by the electrospark deposition method was investigated. To form the Ti-Mo-Si coating, a nonlocalized electrode consisting of titanium granules with the addition of silicon and molybdenum powders was used. The aim of the work is to study the influence of the silicon and molybdenum ratio in the non-localized electrode on the character of mass transfer during the electrospark deposition Ti-Mo-Si coatings, their composition, microstructure, oxidation resistance and tribological properties. To study the phase composition of the coatings, a Dron-7 X-ray diffractometer in CuKα radiation was used. According to the X-ray phase analysis data, the phases of αTi, Mo, Ti5Si3 and TiSi2 were found in the composition of the coatings. The average thickness of the prepared coatings was in the range from 31.70 to 40.97 μm. According to the energy-dispersive analysis data, titanium predominated in the composition of the coatings, the molybdenum concentration reached 18 at. %, and silicon — 9 at. %. It is shown that silicon particles participated disproportionately less in the coating formation compared to molybdenum particles. Oxidation resistance testing showed that the use of the developed Ti-Mo-Si coatings allows increasing the high temperature oxidation resistance of the titanium alloy Ti-6Al-4V at a temperature of 900 °C by up to 5.7 times. The microhardness of the Ti-Mo-Si coating surface was in the range from 5.81 to 9.88 GPa. It was 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 increased 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 highest hardness, wear resistance and oxidation resistance were demonstrated by the coating with the highest silicon content.

The paper presents the results of a study of the chemical and phase composition, structure, physical-mechanical and tribological characteristics of two types of vacuum ion-plasma antifriction carbon coatings alloyed with molybdenum and tungsten, respectively. The first of these types of coatings has a highly oriented linear-chain structure; the second type is an amorphous hydrogenated carbon. The tribotechnical characteristics of the studied coatings were evaluated on a four-ball machine with a modernized friction unit and were carried out both under dry friction and under friction in the boundary lubrication mode in inactive (polyalphaolefin oil PAO-4), surface-active (PAO-4 + 1 % by weight of oleic acid) and chemically active (the same oil + 2 % by weight of DF-11 additive) lubricating environments. It was found that the coating with both “monocrystal” carbon and diamond-like carbon, both alloyed and unalloyed, significantly reduced friction losses and wear of the steel samples to which the coatings were applied, and alloying of these coatings reduced friction almost as much as the studied lubricants. Thus, under dry friction of a ball made of ShKh-15 steel on the cylindrical surfaces of rollers made of the same steel, the friction coefficient obtained was ~ 0.8; when a ball rubs against rollers coated with a molybdenum-doped “monocrystalline carbon” coating, the dry friction coefficient is ~ 0.7; additionally, in an inactive oil environment, this friction pair provides a friction coefficient of 0.12—0.14; and in a chemically active sulfur-containing oil environment, the friction coefficient decreases to 0.05. For a friction pair of steel — molybdenum-doped diamond-like coating, with boundary lubrication by a surface-active composition, the minimum friction coefficient is 0.09. Taking into account the obtained results of the proposed study will allow optimizing the process of creating highly effective lubricants for heavily loaded friction units.

The researches of microstructure changes and structural defects (using the example of dislocation density) of samples made of high-speed steel R6M5 and irradiated with a single high-energy laser pulse as well as the effect of these changes on the abrasive wear resistance of the studied material are presented in the article. It was found that the proposed laser treatment significantly affects the microstructure of the irradiated samples. This is expressed in the almost complete disappearance of the banded distribution of carbides in the samples, which indicates a partial redistribution and dissolution of “heavy” carbides of the Me6C type containing tungsten and molybdenum in the material matrix (martensite). In this case, the configuration of “heavy” Me6C carbides is located between the formulas Fe3(W,Mo)3C – Fe4(W,Mo)2C. Also, exposure to a high-energy laser pulse leads to an increase in the quantity and size of secondary carbides in the alloy matrix, significantly enriched in tungsten and molybdenum. In addition, there is a change in the type of vanadium carbides from Me2C to VC, accompanied by a significant decrease in the amount of molybdenum and tungsten in it. Using the Thixomet image analysis program, it was determined that the number of grains of “heavy” Me6C carbides in terms of volume decreased by 1.30—1.58 times, depending on the distance from the point of interest to the irradiation place of the sample. At the same time, the average size and direction (anisotropy) of the material grains has not changed. The results of X-ray phase analysis showed that after treatment, the number of main phases of the samples remained practically unchanged in distribution, but there was an increase in the responses intensity. Based on the above, the change in the structure defectiveness was determined using the example of dislocation density. The results of abrasive wear tests showed that there is an increase in the wear resistance of irradiated samples by 1.58—2.48 times, depending on the distance from the point of interest to the irradiation place of the sample. In this case, the value of the greatest wear resistance (2.48 times) is achieved with the greatest microstructure changes and structure defectiveness, which corresponds to the distance from the point of interest to the irradiation place of the sample equal to 20 millimeters. The obtained results allow us to recommend the use of the microstructural analysis method for assigning optimal modes of laser hardening of materials.

The structure of the near-surface disturbed layer in diamond single crystals after circular grinding has been studied by electron and atomic force microscopy. It is shown that the size and structure of the disturbed layer are determined by the fractional composition of diamond grains in the diamond-abrasive tool. The structure of the disturbed layer of a single crystal is formed by networks of microcracks with opened and unopened mouths dividing the layer into blocks. The near-surface area of the disturbed layer consists of blocks (1—3 microns) separated by a network of microcracks. Further there is a section of large-sized blocks, passing into a section of blocks located between fragments of broken grains of single crystal. Diamond monocrystal deterioration at diamond-abrasive grinding occurs as a result of two simultaneously occurring processes: formation of a disturbed near-surface layer at dynamic contact interaction of diamond grain tops on the surface of the monocrystal and its destruction at introduction and movement of diamond grain tops in the disturbed layer. Contact interactions of diamond grain tops with the surface of the monocrystal determine its morphology, the structure of the disturbed layer, which affect the colour characteristics of the diamond.

The microstructure, phase composition, mechanical and tribological properties of composites with a BrAMts9-2 bronze matrix, reinforced with tungsten particles have been studied Samples with 0, 5, 10 and 15 vol. % of W particles were obtained by friction stir processing (FSP). It was shown that as a result of multi-pass FSP of tungsten-containing samples, a composite structure is formed from a multiphase bronze matrix consisting of α-Cu solid solution, intermetallic β-Cu3Al and γ2-Al4Cu9 as well as uniformly distributed reinforcement tungsten particles. During tribological tests, all samples demonstrated similar values of coefficient of friction in the range of 0.33—0.39. The wear rate values of composites reinforced with W were significantly lower than those of samples without W. The minimum wear intensity values were obtained on BrAMts9-2/5% W samples. The tribooxidation effect in tungsten-containing samples was accompanied by the formation of the κ-phase of Al2O3 due to the oxidation of the metastable phase γ-Al4Cu9. The resulting composites can be used to fabricate moving parts of machines and devices, high-voltage electrical contacts, heat-removal elements, and many other practical applications.

The article contents the results of examination of cast-iron pipes of water economizers of water-heating boilers, which were in operation in the period of 1986—1991 and which have no external visual defects. We have determined a dependence of wear-out in the form of graphitic corrosion of the surface layer of inner walls of economizer pipes. The researches have been conducted with the use of JSM-6390LV scanning electron microscope equipped with an attachment for conduct of energy-dispersive analysis, and with the use of DuraScan 20 microhardness tester. There are images of areas given, where microhardness testing was performed. The areas were exposed to graphitic corrosion. The dimensions of the layer completely transformed as a result of graphitization and the transition zone were determined. The microhardness of the layer completely transformed as a result of graphitization and the transition zone was measured. It was found that the microhardness of these zones is significantly lower than the microhardness of gray cast iron. We have also presented the results of energy-dispersive analysis and specific diagnostic features identifying the graphitization process. In the article we propose a method of assessment of supporting capacity of cast-iron pipes of water economizers based on the rate of their graphitization. A mathematical model takes into account all main properties, features, physical and geometric characteristic of the real structure, which has an analytical model represented by a beam rigidly restrained on both heads, and which is bending by well-distributed dead weight load arised from the pipe’s own weight and the weight of the water flowing through it. The calculated residual wall thickness of 4.53 mm after wear of its internal cylindric surface is comparable with the known empirical data of statical analysis of emergency situations at economizers. The data given in the article could be used by specialists for expert examination of cast-iron pipes of economizers, as well as for justification of their sorting or life extension.

Dry sliding of model samples of C235 steel against 45 steel under alternating current with a density of up to 120 A/cm2 using the pin-on-ring configuration was investigated. The possibilities of increasing wear resistance by changing one of the geometric parameters (height) of the sample (pin) were studied and the temperature of the sample holder at different points was investigated. It was shown that this temperature can exceed 150 ℃ in the sample mounting zone. The increase in the temperature of the sample holder and the wear intensity were nonlinear in accordance with a curve close to an exponential function with increasing current density. Sliding at a current density higher than 100 A/cm2 occurred under conditions of catastrophic wear. Formation of a transfer layer with a thickness of about 20 μm was observed on the contact surface of the samples. Using X-ray phase analysis, it was found that the transfer layer contains more than 70 % FeO. The analysis of wear surfaces allowed to reveal the mechanism of contact layers deterioration, which was presented as the division of the nominal contact area into two sectors. The boundary between the sectors was quite clear and perpendicular to the sliding direction. The sector directed towards the oncoming contact surface of the counterbody had traces of adhesion, plowing, etc., which usually appear during sliding without current. The other sector had signs of deformation similar to the deformation of a viscous liquid. Traces of adhesion were not observed here. The friction coefficient decreased with increasing current density and did not change its behavior upon transition to the catastrophic wear mode. The presented regularities were observed at a qualitative level regardless of the height of the samples. Only the heating temperatures of the sample holder differed quantitatively. The results of the work will be useful in creating a real friction unit operating in sliding current collection with a high current density.

The article is devoted to the calculation of the acting forces and amplitude-frequency characteristics for the rotor-stator system in a state of frictional contact. Unlike the known approaches, the normal pressure force between the rotor and stator is determined not only by the elasticity and damping of their materials at the point of contact and/or stator supports, but also by the bending complex stiffness of the entire rotor, which has conditionally received an additional bearing with a clearance. Such a quasi-static reaction of the rotor to contact with the stator, initially with Coulomb friction between them, is expanded to a dynamic contact with rolling friction of the rotor on the stator, dependent on the normal pressure force between them. In the proposed mathematical model and in the considered practical example, the motion equations are composed and solved in matrix form relative to the precession velocity and rotor displacements, based on the system (interrelated with the stator) elastic-inertial characteristics, as well as the coefficients of slipping and rolling friction, internal and external losses. The calculations established the final ranges of possible angular velocities for the continuous rolling of the rotor around the stator and showed the possibility of eliminating it by correcting only two system parameters, they are the rotor damping coefficient and the elastic modulus of the stator contact surface.

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 scheme “finger—disc” on the friction machine MMW-1. The thermal effect during friction was modelled by 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.