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 quality parameters of surface layers synthesised using electrospark alloying (ESA) technology were analysed in this paper. The main focus was on the influence of equipment energy parameters on structure formation, specifically the effect of discharge energy and productivity. Microstructural analysis of the modified surface of C40 steel after nitriding by ESA using a paste containing nitrogen compounds injected into the interelectrode gap was conducted. The layer structure for all studied ESA parameters includes three areas: the upper “white layer”, the diffusion zone below it, and the substrate. The roughness of the surface is Ra ∼ 0.9 μm at low discharge energy Wp = 0.13 J and Ra ∼ 6 μm at Wp = 3.4 J. The microhardness, continuity, and surface roughness of the layers varied with Wp. The influence of ESA productivity on the structure was studied. The thickness of the hardened layer and the diffusion zone, as well as the microhardness and continuity, are affected by reduced productivity. For the same discharge energy, the thickness of the hardened layer increases by 10-18% with a decrease in productivity compared to the classical mode.

electrospark alloying, discharge energy, productivity, coating, structure

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

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 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 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 Mo-electrode 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.

X-ray diffraction, Nanostructures, Nanotubes

This paper presents an analysis of various technologies, including such as aluminization, cementation, nitriding, and nitrocementation, to increase the quality parameters of surface layers of parts, performed by electrospark alloying (ESA) and by additional saturation of surfaces with alloying elements from special technological environments (STE). During aluminization, the thickness of the "white" layer and the diffusion zone, as well as the microhardness, coating continuity and roughness of the surface increased as the discharge energy (Wp) increased. The layer consists of iron-aluminium intermetallics and free aluminium. It has been proposed to perform the ESA process with the same electrode (aluminium), but at lower energies, in order to reduce the surface roughness and obtain continuous coatings. The comparative study of the parameters of the quality of the layers after the traditional cementation - ESA with carbon electrode (CESA) and after the proposed one has shown that after the treatment of the surface with the use of the proposed technology, the roughness of the surface decreases. Simultaneously, the continuity of the doped layer increases up to 100%, the depth of the carbon diffusion zone increases up to 80 µm, and the microhardness and "white" layer thickness increase to 9932 MPa and 230 µm, respectively. The analysis of the structure-forming characteristics of the surface layers of carbon steel after ESA nitriding and nitrocarburising using STE has shown that the layer structures obtained consist of the following three areas, such as the non-etchable "white" layer, the modified diffusion zone and the substrate. Thickness, microhardness of the coating zones, integrity of the "white" layer, and surface roughness also increase as the discharge energy increases.

Electrodes, Hardness, Metallurgy, Surface hardening

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