Institute of Fundamental Technological Research

Electrospark coatings alloyed with MoS2 have been studied. The coatings were obtained by the following two strategies: the first consisted of pre-applying molybdenum disulfide to the treated surface and alloying with a molybdenum electrode (Mo + MoS2 coating); the second consisted of applying a paste with a sulfur content of 33.3% to the treated surface and alloying with a molybdenum electrode (Mo + S coating). The structure, phase composition, and tribological properties of the coatings were investigated. The coatings have a complex structure consisting of an upper soft layer, a hardened white layer, a diffusion zone, and a substrate. Element analysis and cross-sectional hardness changes indicated that element diffusion occurred at the coating/substrate interface. The phase composition of the coatings is represented by BCC and FCC solid solutions on Fe, and MoS2 is also detected. In Mo + S coatings, the molybdenum disulfide on the surface is about 8%; in Mo + MoS2 coatings, it is 27%–46%. The obtained coatings show very good tribological properties compared to molybdenum ESA coatings. The frictional forces and coefficients are reduced by a factor of 10 and 40, depending on the test conditions.

electrospark alloying, coating, structure, molybdenum disulfide, tribological properties, energy conservation

The paper presents an analysis of technologies for improving the quality parameters of the surface layers of parts, which were carried out by the method of electrospark alloying (ESA) and by additional saturation of surfaces with alloying elements from special process media (STM). The technology of sulfocementation was considered. Metallographic and hardness tests after sulfocementation by ESA showed that the treated surface consists of layers: "soft", hardened and base metal. As the discharge energy increases, the thickness, microhardness and integrity of the coating increase. The presence of sulfur in STM promotes the sulfidation process. It is shown that sulfur accumulates on the surface of the metal at a depth of up to 30 μm. This zone is characterized by reduced microhardness. A strengthened layer is formed under this layer, it has an increased carbon content and high microhardness.

electro-spark alloying, special technological environment, coating, sulfocementation, microstructure, microhardness

A new method of nanostructuring of the surface by electrospark alloying method (ESA) using special processing media (SPM) with carbon nanotubes is proposed. The influence on the ESA regimes and the composition of the SPM on the microstructure and hardness of the coatings has been considered. While processing the Armco iron, with an increase in the discharge energy, the thickness and continuity of the coating increase. In the microstructures, the nanoscale phases of 40 nm to 1300 nm are detected, and they are evenly distributed in the coatings. Adding nanotubes helps to increase the continuity, thickness and hardness. Because of the ESA process, coatings with a uniform distribution of molybdenum are formed. Carbon, apparently in the form of the carbon nanotubes, is concentrated on the surfaces of the samples being processed, regardless of the discharge energy during the ESA process. The use of the proposed ESA method has a positive effect on the quality parameters of the coating.

The analysis of the influence of the parameters of electrospark alloying with an aluminium electrode on the quality (roughness, microstructure of the coating, its continuity, phase composition, and microhardness) of the aluminized layer is presented. The effect of finishing methods after aluminizing is evaluated. The heat resistance of the obtained coatings is studied. Metallographic analysis shows that the coating consists of three sections: a ‘white’ layer, a diffusion zone, and the base metal. With an increase in the discharge energy, such quality parameters of the surface layer as thickness, microhardness of both a ‘white’ layer and a transition zone, and roughness are increased. The continuity of a ‘white’ layer at the discharge energy Wp = 0.52 J is low (of 50–60%); with a subsequent increase in the discharge energy, it increases and, at Wp = 6.8 J, it is of 100%. An increase in the discharge energy during electric-spark alloying (ESA) leads to a change in the chemical and phase compositions of the layer: at low discharge energies, a layer is formed, consisting mainly of α-Fe and aluminium oxides. As Wp increases, the layer consists of iron and aluminium intermetallic compounds, as well as free aluminium, that is confirmed by the data of local x-ray microanalysis. For practical application, it is possible to recommend the process of aluminizing by the ESA method, using the modes (discharge energy in the range of 4.6–6.8 J and productivity of 2.0–3.0 cm2/min). Such process provides the formation of a ‘white’ layer with a thickness of 70–130 µm, microhardness of 5000–7500 MPa, roughness (Ra) of 6–9 µm, and continuity of 95–100%. In order to increase the thickness of the aluminized layer, it is recommended to preliminarily apply grease containing aluminium powder to the steel surface and, without waiting for it to dry, carry out ESA with an aluminium electrode. In this case, the coating continuity is of 100%, the layer thickness is of up to 200 µm, and the microhardness is of 4500 MPa. The paper presents the results of study of the quality parameters of multicomponent aluminium-containing coatings of Al–S, Al–C–S, and Al–C–B systems. Replacing the aluminium electrode with graphite one leads to a decrease in the thickness and continuity of a ‘white’ layer, respectively, to 50 µm and 30%. In turn, the microhardness on the surface increases to 9000 MPa. The addition of 0.7 boron to the consistency substance leads to an increase in the thickness and continuity of a ‘white’ layer, respectively, up to 60 µm and 70%. The microhardness on the surface rises to 12000 MPa. In order to reduce the roughness of the surface layer and to obtain continuous coatings, it is recommended to carry out ESA with an aluminium electrode, but at lower modes.

electrospark alloying, coating, aluminizing, microhardness, continuity, roughness, structure, x-ray diffraction analysis, x-ray spectral analysis

In this paper, the authors discuss the method of deformations compensation (resulting from the impact of variable temperatures and pressure) in pipelines intended for fluids transport (liquids and gases). Classical methods of compensation through the so-called "natural compensation" and using special devices called expansion joints. In this paper authors present research work on a new type of the metal expansion joints, called bellow-lens expansion joints. The mechanically assisted laser forming method, which was used to manufacture the bellow-lens expansion joints, was presented. The method uses CO2 laser radiation to heat the element from which the expansion joint will be made and the proprietary system consists of an actuator and swivel handle.

metal expansion joints, laser forming, pipelines compensating, pipelines thermal deformation

The article describes a new method of forming the protective coatings of steel parts operating under conditions of abrasive wear both in general mechanical engineering, the composition of which is of 90% ВК6 + 10% 1М, and in industries, where there may be radiation exposure and the composition of 1М (70% Ni, 20% Cr, 5% Si, 5% B), by applying them by the method of electrospark alloying (ESA) with compact electrodes-tools made of nichrome wire X20Н80 and ВК6 hard alloy and using special technological media (STM), which include the necessary alloying elements. As a result of these research, it is established that the surface layers of the 45 and Р6M5 steels after applying wear-resistant coatings have a structure that consists of three areas: the ‘white layer’, the transition zone below, and the base metal. When the discharge energy (Wp) increases from 0.52 to 2.6 J, the thicknesses of the ‘white layer’ and the transition zone, their microhardness and surface roughness increase, but the integrity of the applied coating decreases. The highest microhardness of 9750-12800 and 14250-14600 MPa corresponds to the coating formed on steel 45 and Р6M5, respectively, during ESA by means of both the compact electrodes-tools made of hard alloy ВК6 and the STM with the composition of 0.5% Si + 0.5% B + 2% Cr + 7% Ni + 90% Vaseline.

electrospark alloying, electrode tool, coating, white layer, microhardness, roughness, continuity

In the article, as a result of comparative tests, it is established that steel samples with a coating applying the electrospark alloying method (ESA) with a BK6 hard-alloy electrode with the use of a special technological environment (STE) with a composition of 0.5%Si + 0.5%B + 2%Cr + 7%Ni + 90% vaseline, the wear of which after 24 hours of testing is of 221 mg that is 122% less than that for samples without coating and 15% and 31% for samples with coatings applying the nichrome-electrodes’ wire X20H80 using STE composition of 0.5%Si + 0.5%B + 59%BK6 + 40% vaseline and STE composition of 5%Si + 5%B + 90% vaseline, respectively, and by 22% and 47% less than with coatings applying the electrodes made by the method of powder metallurgy (PM), the composition of which is of 90%BK6 + 10%1M and 1M, respectively. For P6M5 steel, better resistance against hydroabrasive wear is possessed by samples with a coating applying the ESA method with an electrode made of hard alloy BK6 using STE composition of 0.5%Si + 0.5%B + 2%Cr + 7%Ni + 90% vaseline, the wear of which after 24 hours of testing is of 188 mg that is 43% less than in samples without coating and by 6% and 15% in samples with a coating applying the ESA method with an electrode made of nichrome wire of the composition X20H80 using STE composition of 0.5%Si + 0.5%B + 59%BK6 + 40% vaseline and STE composition of 5%Si + 5%B + 90% vaseline, and by 24% and 27% less than with coatings applying the electrodes produced by the PM method with a composition of 90%BK6 + 10%1M and 1M, respectively. In ESA with electrodes-tools made both by the PM method and by the new technology of wire X20H80 and hard alloy BK6 and STE, parts made of steel 45 and steel P6M5 have a decrease in the strength limit and yield limit, respectively, and both the relative elongation and the relative narrowing increase. With further abrasive-free ultrasonic finishing (AFUF), both the strength limit and the yield strength increase, and both the relative elongation and the relative narrowing decrease. For practical implementation, wear-resistant coatings formed according to the new technology, using tool electrodes made of X20H80 wire and hard alloy BK6 and STE in two stages with the following AFUF are proposed, the growth of the strength limit and the yield limit of which increase for steel 45 and steel P6M5 by 4.9% and 4.6% and 3.5% and 2.7%, respectively, and relative elongation and relative contraction decrease by 1.7% and 1.3% and 2.0% and 1.7%, respectively. At the same time, the surface roughness is Ra = 1.1 μm, and the integrity is of 100%

electrospark alloying, electrode tool, coating, white layer, microhardness, roughness, integrity

The structure formation and properties of the surface layers of steel parts after alloying by traditional technologies and the method of electrospark alloying (ESA) is analysed in the article. As a result of the study of the productivity of the ESA process by aluminium electrode-tool, which is one of the important parameters of the ESA technology, reserves are revealed for improving the quality of the surface layers of steel parts during aluminizing. Two options for reducing productivity in relation to the traditional are studied: the first one, when productivity is reduced by ≅ 2 times; the second one, when performance is reduced by ≅ 4 times. As established, in the first variant, when the discharge energy increases from 0.52 to 6.8 J, at the first stage of aluminizing of steel 20 and steel 40, the thickness of the ‘white’ layer from 20 to 75 and from 25 to 110 μm, respectively; the thickness of the diffusion zone increases from 35 to 120 and from 40 to 140 μm, respectively; the microhardness of the ‘white layer’ increases from 2200 to 7400 and from 2400 to 7450 MPa, respectively; the surface roughness Ra increases from 1.1 to 9.0 and from 1.0 to 8.1 μm, respectively, and the continuity increases from 80 to 100% starting with Wp = 4.6 J and from 60 to 100% at Wp = 6.8 J. In the second variant, when the discharge energy increases from 0.52 to 6.8 J, at the first stage of processing steel 20 and steel 40, the thickness of the ‘white’ layer increases for steel 20 from 25 to 60 μm at Wp = 4.6 J, and then it doesn’t change for steel 40 from 30 to 100 μm; the thickness of the diffusion zone increases from 45 to 130, respectively; the microhardness of the ‘white layer’ increases from 2250 to 7300 and from 2450 to 7300 MPa, respectively; the surface roughness Ra increases from 1.3 to 9.0 and from 1.6 to 8.1 μm, respectively, and the continuity for both steel 20 and steel 40 at Wp = 0.52 J is of 95% and further increases to 100%.

electrospark alloying, aluminizing, productivity, surface layer, structure, roughness, microhardness, thickness of the white layer, coating continuity

The microstructure, phase composition, and microhardness of the cast high-entropy VNb2TaCrMoW alloy with the addition of titanium diboride were studied. The initial VNb2TaCrMoW alloy consisted of two bcc solid solutions, slightly differing in lattice parameters (a = 0.3139 nm and 0.3200 nm). The addition of boron as titanium diboride and repeated remelting led to a bcc solid solution with a larger lattice parameter (a = 0.3217 nm) and a boride with W3.5Fe2.5B4 structure (a = 0.6054 nm and c = 0.3256 nm). The bcc solid solution was the first to crystallize, and the boride was part of the eutectic grains and precipitated from the last melt portions, forming a closed network. The resulting alloy was applied to a carbon steel substrate as a coating using electrospark deposition employing an Elitron-24A installation with varying electrical pulse energy. Higher pulse energy during coating deposition increased the layer thickness and surface roughness but did not influence the phase composition. The microstructure of the coatings was more uniform compared to the cast alloys, and X-ray diffraction showed that the coatings contained bcc solid solutions, Fe7W6 intermetallic compound, and a small amount of TaO2 oxide. The coatings had a hardness of about 10 GPa and were 11–15 μm and 16–20 μm thick at discharge energies of 0.52 and 1.1 J, respectively. A comparative analysis of the phase composition, hardness, and microstructure of the cast alloy and associated coatings was carried out. The coatings deposited at a discharge energy of 0.52 J were subjected to laser processing. Laser processing of the coatings resulted in a thermally affected zone, while the surface layer hardness hardly changed. The wear resistance of the coatings deposited at a discharge energy of 0.52 J was analyzed. Wear resistance testing was conducted for three counterface materials (VK6, Al2O3, and Si3N4) in quasistatic and dynamic loading modes. Laser processing of the electrospark coatings changed the wear mechanism and significantly increased the wear resistance regardless of the counterface material and loading mode.

high-entropy boride, electrospark deposition, solid solution, wear resistance, microstructure, X-ray diffraction

A new method of surface modification based on the method of electrospark alloying (ESA) using carburizer containing nitrogen—carbon components for producing coatings is considered. New processes have been proposed that include the step of applying saturating media in the form of paste-like nitrogenous and nitrogenous-carbon components, respectively, onto the surface without waiting for those media to dry, conducting the ESA process with the use of a steel electrode-tool, as well as with a graphite electrode-tool. Before applying the saturating media, an aluminium layer is applied onto the surface with the use of the ESA method at a discharge energy of Wp = 0.13–6.80 J. A saturating medium in the form of a paste was applied to the surfaces of specimens of steel C22 and steel C40. During nitriding, nitrocarburizing and carburization by ESA (CESA) processes, with an increase in the discharge energy (Wp), the thickness, micro hardness and continuity of the “white layer” coatings, as well as the magnitude of the surface roughness, increase due to saturation of the steel surface with nitrogen and/or carbon, high cooling rates, formation of non-equilibrium structures, formation of special phases, etc. In the course of nitriding, nitrocarburizing and CESA processing of steels C22 and C40, preliminary processing with the use of the ESA method by aluminum increases the thickness, microhardness and continuity of the “white layer”, while the roughness changes insignificantly. Analysis of the phase composition indicates that the presence of the aluminum sublayer leads to the formation of the aluminum-containing phases, resulting in a significant increase in the hardness and, in addition, in an increase in the thickness and quality of the surface layers. The proposed methods can be used to strengthen the surface layers of the critical parts and their elements for compressor and pumping equipment

electrospark alloying,coatings,roughness,structure,microhardness,continuity,X-ray diffraction analysis,nitriding,nitrocarburizing,carburization

The technical and economic efficiency of new PCMs depends on the ability to predict their performance. The problem of predicting the properties of PCMs can be solved by computer simulation by the finite element method. In this work, an experimental determination of the physical and mechanical properties of PTFE PCMs depending on the concentration of fibrous and dispersed filler was carried out. A finite element model in ANSYS APDL was built to simulate the strength and load-bearing capacity of the material with the analysis of damage accumulation. Verification of the developed computer model to predict the mechanical properties of composite materials was performed by comparing the results obtained during field and model experiments. It was found that the finite element model predicts the strength of chaotically reinforced spherical inclusions of composite materials. This is due to the smoothness of the filler surfaces and the lack of filler dissection in the model. Instead, the prediction of the strength of a finite element model of chaotically reinforced cylindrical inclusions of composite materials requires additional analysis. The matrix and the fibrous filler obviously have stress concentrators and are both subject to the difficulties of creating a reliable structural model

PCMs, polytetrafluoroethylene, carbon fiber, coke, energy efficiency, modeling, strength, solid model, finite element model

The article reviews and analyses the current scientific research in the field of surface treatment of metal surfaces with concentrated energy fluxes (CEF) — the electric-spark (in the literature, known also as electrospark) alloying (ESA), which makes it possible to obtain surface structures with unique physical, mechanical and tribological properties at the nanoscale. The ESA method with a graphite electrode (electrospark carburizing — EC) is based on the process of diffusion (saturation of the surface layer of a part with carbon), and it is not accompanied by an increase in the size of the part. In this article, the influence of the EC parameters on the quality of the carburized layer is investigated. The microstructural analysis shows that the three characteristic zones could be distinguished in the structure: the carburized (‘white’) layer, the finely dispersed transition zone with fine grain, and the base metal zone. The analysis of the results of the durometric studies of the coatings is carried out. To achieve the required parameters of dimensional accuracy and roughness of the working surface of the part after the EC process, it is necessary to use the method of non-abrasive ultrasonic finishing (NAUF). In addition, because of applying the NAUF method, the surface roughness is decreased, the tensile stresses are changed to the compressive ones, and the fatigue strength is increased too. In addition, to reduce the roughness of the treated surface, it is proposed to apply the EC technology in stages, reducing the energy of the spark discharge at each subsequent stage. In order to increase the quality of the carburized layer obtained by the EC process, it is proposed to use a graphite powder, which is applied to the treated surface before alloying. The comparative analysis shows that, after the traditional EC process at Wp = 4.6 J, the surface roughness of steel 20 is Ra = 8.3–9.0 μm, and after the proposed technology, Ra = 3.2–4.8 μm. In this case, the continuity of the alloyed layer increases up to 100%; there increases the depth of the diffusion zone of carbon up to 80 μm as well as the microhardness of the ‘white’ layer and its thickness, which increase up to 9932 MPa and up to 230 μm, respectively. The local micro-x-ray spectral analysis of the obtained coatings shows that, at the EC process carried out in a traditional way, the applying Wp = 0.9, 2.6, 4.6 J provides the formation of the surface layers with high-carbon content depths of 70, 100, 120 μm, respectively, and with the use of a graphite powder, they are of 80, 120, 170 μm. While deepening, the amount of carbon is decreasing from 0.72–0.86% to the carbon content in the base metal — 0.17–0.24%. In the near-surface layer formed with the use of the new technology, the pores are filled with free graphite, which could be used as a solid lubricant to improve the operating characteristics of the friction-pairs parts processed thereby

electrospark (electric-spark) alloying, graphite, carburizing, microstructure, quality, wear resistance

In article we present the results of studies of the structural state of coatings formed by the method of electrospark alloying at the discharge energy Wp = 0.13, 0.52 and 0.9 J by anodes from nickel and stainless steel X10CrNiTi18-10 on the cathode surface from X10CrNiTi18-10 steel. Anode materials, such as nickel and X10CrNiTi18-10 steel are recommended as materials, which is advisable to use for restoring the surfaces of parts from X10CrNiTi18-10 steel operating in conditions of radiation exposure. Metallographic analysis of the formed coatings showed that their microstructure consists of 3 zones: 1) ‘white layer’ is the layer that cannot be etched with conventional reagents, 2) transition zone or diffuse zone, 3) base metal. Using nickel and steel X10CrNiTi18-10 with increasing discharge energy, the thickness of the hardened layer, microhardness, continuity and thickness of the white layer, as well as the surface roughness are increased. Replacing the nickel anode with steel X10CrNiTi18-10 surface roughness is increased and the thickness of the hardened layer is decreased.

electrospark alloying, nickel, steel, metallographic analysis, structure, layer thickness, microhardness, roughness, continuity

Eight alloys of the Ti–Nb–Mo system are synthesized by the arc remelting method. As shown, they have dendritic microstructures typical of casting. The phase composition and lattice periods of the formed phases are determined. Using the method of differential thermal analysis (DTA), phase transformations in the solid state are investigated, and the temperatures of the onset of melting and crystallization are determined. For alloys, the solidus temperature of which is above 2000°C, together with DTA, the Pirani–Althermum pyrometric method is also used. Based on the experimental data, the temperature dependences of the hardness of the alloys are constructed and the activation energies of deformation of the material under the indenter are calculated. The analysis of the curves of the dependence of the hardness of the alloys is carried out and the temperature of the sharp softening of the material is determined. As shown, that the α→β transition in titanium alloys with an unstable β-phase does not lead to a significant change in hardness.

solidus temperature, hot hardness, high-temperature strength, titanium alloys, crystal structure

in article we present the results of studies of the local x-ray spectral analysis of coatings formed by the electrospark alloying (ESA) method at the discharge energy Wp = 0.13, 0.52 and 0.9 J by anodes from nickel and stainless steel X10CrNiTi18-10 on the cathode surface from X10CrNiTi18-10 steel. During ESA by stainless steel X10CrNiTi18-10 anode with an increase Wp in characteristic points and from the entire investigated surface of the coating, the quantitative elemental composition is not changed. The analysis of elements distribution over the depth of the formed layer is showed that when using the electrode tool from steel X10CrNiTi18-10 with an increase in Wp, there are a slight decrease in chromium and an increase in nickel and titanium in the surface layer. When steel X10CrNiTi18-10 is replaced by nickel with an increase in Wp, the concentration of nickel on the coating surface decreases from 95.38 to 89.04%. As the recession deepens from the coating surface, the concentration of nickel gradually decreases, respectively, at Wp = 0.13, 0.52 and 0.9 J from 96.29, 90.29 and 89.04% on the surface to 9.0, 10.30 and 9.9% at depth: 120, 165 and 240 μm. At the same time, the concentration of chromium, titanium and iron gradually increases.

electrospark alloying, nickel, steel, x-ray spectral analysis, scan step, topography, spectrum

The article substantiates the importance and relevance of increasing problem of the performance and service life of babbitt sliding bearings (SB), which are the rotors supports of a large number of centrifugal pumps, compressors, turbines and other dynamic equipment operating at high operating parameters (speeds, loads and temperatures), as well as in conditions of corrosive, abrasive and other types of working environment’s influence. The analysis of the babbitt SBs production technology and operating conditions showed that the reason for the decrease in their durability are factors that are formed both at the stage of manufacture and during operation. SB failure under normal operating conditions is a consequence of wear various types: cavitation, abrasive wear, damage due to plastic deformations, fatigue damage, etc. The antifriction layer wear resistance depends on the mode of operation and design of the bearing, the physical properties of the connection between the layer and the base, the rigidity of the shaft and the bed under the bearings. As established, the bearing anti-friction layer quality must be evaluated according to the following criteria: adhesion strength of the coating to the base, cohesive strength of the anti-friction layer, porosity, and homogeneity of the structure. As established, during the production of SBs, the formation by the method of electrospark alloying (ESA) of a copper intermediate layer, firmly bonded with steel substrate, and tin layer (formation of solid substitution solutions) and babbitt provides a stronger (by 35%) of adhesion, compared to traditional technology (steel 20 + babbitt), steel substrate with babbitt, as well as more intensive removal of heat from the friction zone. As determined, a new technology in which all operations are carried out by the ESA method can be a reserve for improving the babbitt coatings formation quality, which significantly affects the durability of the SB. As determined, in order to determine a more rational technology for applying babbitt coatings, it is necessary to develop a physically based mathematical model that relates the wear of a certain amount of babbitt to the frictional work spent on it.

sliding bearing, babbitt, coating, wear, structure, transition layer, adhesion strength, electrospark alloying, mathematical model

in the article, a direct choice system of the most rational technology for applying a babbitt coating on the liners of sliding bearings (SB) is developed, which takes into account both economic and environmental requirements. On the basis of the performed research, a physically substantiated mathematical model of the babbitt-coatings’ wear process (wear equation) is proposed, which allows solving both the direct problem of determining weight and linear wears based on the known work of friction, as well as the inverse problem of finding the necessary work of friction to obtain the required amount of weight or linear wears. With knowing the time to reach a certain amount of wear, it becomes possible to operate the products more rationally, timely assigning the repair time and friction-surface catastrophic-wear preventing. In the course of research, a methodology is developed for determining the constants of the wear equation: activation energy (EA) as well as maximum weight (Δmб.п.н) and linear (Δhб.п.н) wears, which can be used as selection criteria for the most rational technology of applying a babbitt coating

sliding bearing, babbitt, coating, wear, structure, transition layer, adhesion strength, electrospark alloying, mathematical model

There have been considered the coating structure modification after electrospark alloying (ESA) by the Moelectrode using a paste with carbon nanotubes. It was showed that the regimes and composition of the paste influenced the microstructure, continuity, roughness, and hardness of the coatings. The microstructures after the ESA of the Armco iron were studied. The use of higher discharge energy in ESA leads to an increase in surface roughness, coating thickness, and coating continuity. The use of higher discharge energy during ESA results in an increase in surface roughness, coating thickness, and coating continuity. The microstructures reveal nanoscale phases from 40 to 60 nm, which are evenly distributed in the coatings. The addition of ARKEMA nanotubes increases the hardness to 608 HV. The results of local X-ray diffraction analysis showed that carbon is concentrated on the surface, while molybdenum is distributed homogeneously in the coating. The addition of nanotubes to the paste before ESA improves hardness and continuity. The effect of nanotubes on the structure and properties of coatings is positive.

The paper analyzes the works devoted to solving problems affecting the bearing life of rolling bearings (RB) and to revealing reserves for its increase. There proposed a new technology for forming a protective coating on the shaft bearing journal or on the surface of a sleeve pressed thereon, which consists in the use of a combined technology comprising a process for stage-by-stage aluminizing by the method of electrospark alloying (A ESA ) followed by a process of ion nitriding (IN). Such a coating has a 100% continuity, the greatest thickness of the increased hardness zone of 300 µm, the surface microhardness of 7700 MPa, and the roughness (Ra) after non-abrasive ultrasonic finishing (NAUF) of 0.5 µm, The results of the X-ray microanalysis indicate that an increased content of aluminum is observed in the surface layer at the distance of up to 40 µm after the stage-by-stage AESA process. The research results have shown that in order to restore the shaft bearing journal neck surface layer hardness, which had been lost because of the repair work, the step-by-step AESA technology is more preferable. Thus, when removing the surface layer to a depth of 0.15 mm and subsequently carburizing by the method of electrospark alloying (C ESA ), the maximum microhardness of the surface layer is 7250 MPa, and the thickness of the zone of the increased hardness is 150 µm, At subsequently processing by the AESA method, these quality parameters of the surface layer are, respectively, 7350 MPa and 210 µm. The use of the NAUF method, both after C ESA and AESA processes, makes it possible to reduce the surface roughness up to Ra = 0.5 µm. To decrease the surface roughness of the RB housing seat, it is advisably to practice burnishing with a diamond tool (DB) after the A ESA process