A technology is proposed to increase the hardness and wear resistance of the surface of R6M5 high-speed tool steel using low-temperature plasma electrolytic nitrocarburizing in combination with air quenching and three-stage tempering. The structure and phase composition of the surface layers of high-speed steel before and after treatment were studied. It was shown that the formation of a high-alloy martensite structure with nitride inclusions after nitrocarburizing with quenching and the precipitation of finely dispersed carbides during subsequent tempering leads to hardening of the surface layer to 1140 HV after quenching and to 1380 HV after subsequent tempering.

The possibility of using plasma electrolytic technologies for surface treatment of 16MnCr5 steel in order to increase its wear resistance is shown. The influence of electrophysical characteristics of plasma electrolytic treatment on structural-phase changes of the surface and its tribological properties is studied. A comparison of anodic and cathodic variants of diffusion saturation, as well as subsequent polishing on the results of surface modification is carried out. The complex effect of surface layers strengthened above 1100 HV, including iron carbide and nitride, martensite and retained austenite, to a depth of up to 250 mu m with the preservation of a viscous core and the formation of a relatively homogeneous surface with reduced roughness on increasing wear resistance has been revealed. The features of tribological behavior of surfaces formed under different electrophysical parameters of processing, mainly related to the difference in surface microrelief, are shown. The correlation of the Kragelsky-Kambolov criterion as a complex assessment of surface roughness with its wear resistance is shown. The influence of changes in sliding speed and friction load on the occurrence and development of leading processes that determine the intensity and nature of destruction of friction surfaces is established.

The paper investigates the feasibility of plasma electrolytic treatment (PET) of 90CrSi tool steel to enhance hardness and wear resistance. The influence of electrophysical parameters of PET (polarity of the active electrode, chemical-thermal treatment, and polishing modes) on the composition, structure, morphology, and tribological properties of the surface was studied. Tribological tests were carried out under dry friction conditions according to the shaft-bushing scheme with fixation of the friction coefficient and temperature in the friction contact zone, measurements of surface microgeometry parameters, morphological analysis of friction tracks, and weight wear. The formation of a surface hardened to 1110–1120 HV due to the formation of quenched martensite is shown. Features of nitrogen diffusion during anodic PET and cathodic PET were revealed, and diffusion coefficients were calculated. The wear resistance of the surface of 90CrSi steel increased by 5–9 times after anodic PET followed by polishing, by 16 times after cathodic PET, and up to 32 times after subsequent polishing. It is shown that in all cases, the violation of frictional bonds occurs through the plastic displacement of the material, and the wear mechanism is fatigue wear during dry friction and plastic contact.

The positive effect of plasma electrolytic treatment on CrWMn tool steel to increase the wear resistance of its surface is shown. The effect of plasma electrolytic nitriding and subsequent polishing on the structure, phase and elemental composition, microhardness of the surface layer, and surface morphology is established. Steel nitriding leads to the formation of a modified surface layer including Fe2–3N iron nitride and nitrogen martensite, below which hardening martensite is formed, reaching a microhardness value of 1200 HV. Subsequent polishing leads to a decrease in surface roughness by 42–68%. Tribological tests were carried out according to the shaft-bushing scheme. A decrease in the friction coefficient and weight wear of up to 2.6 and 30.1 times, respectively, is shown. The formed structure of the surface layer compensates for the effect of the counter body and determines the destruction of friction bonds by plastic displacement. The wear mechanism has been established and is defined as fatigue wear under dry friction and plastic contact.

The paper examines the possibility of increasing the wear and corrosion resistance of a CP-Ti surface by duplex plasma electrolytic treatment (borocarburizing and polishing). The structure and composition of diffusion layers, their microhardness, surface morphology and roughness, wear resistance during dry friction and corrosion resistance in Ringer’s solution were studied. The formation of a surface-hardened layer up to 200 μm thick with a microhardness of up to 950 HV, including carbides and a solid solution of boron and carbon, is shown. Subsequent polishing makes it possible to reduce surface roughness and remove weak areas of the porous oxide layer, which are formed during high-temperature oxidation in aqueous electrolyte vapor during borocarburizing. Changing the morphology and structural-phase composition of the CP-Ti surface helps reduce weight wear by a factor of three (the mode of frictional interaction changes from microcutting to oxidative wear) and corrosion current density by a factor of four after borocarburizing in a solution of boric acid, glycerin and ammonium chloride at 950 °C for 5 min and subsequent polishing in an ammonium fluoride solution at a voltage of 250 V for 3 min.

The proposed review presents the results of the analysis of the equipment and technological methods for implementing the plasma electrolytic chemical-thermal treatment and plasma electrolytic polishing. A group of methods based on the immersion of workpieces in an electrolyzer was considered, as well as a method of a local treatment by the jet feed of an electrolyte to the area of the surface being treated. The influence of the design and characteristics of the electrolyzer, the power source and the system for feeding the work-piece into the electrolyte on the specifics of plasma electrolytic treatment methods is shown. Technological methods improving the quality and productivity of treatment are considered. Limitations in the applicability of the existing equipment were revealed, and the prospects for the improvement in the field of development of equipment and technologies for plasma electrolytic treatment were determined.

Corrosion behavior of So-W coatings obtained from citrate electrolyte (with W content in the coating of about 24 att. %) in the following corrosive environments was studied by the methods of electrochemical impedance and polarization measurements: 0.6M sodium chloride (3.5 mass%), 0.1 M sodium sulfate (Na2SO4), 1 M hydrochloric acid (HCl) and 0.5M sulfuric acid (H2SO4). As a comparison, JIS-SK5 steel, which acts as a substrate during deposition, was taken. It is shown that the corrosion current of Co-W coatings in three corrosive media (sodium chloride, hydrochloric acid and sodium sulfate) is close to 20 +/- 3 mu A/cm(2). When exposed to acidic environments, the corrosion potential of Co-W coatings shifts to the anodic region reaching values of -0.260 V, and in neutral environments (chloride and sulfate) it reaches significantly higher values of -0.76 V. The high passivating ability of the Co-W coating in used acids is demonstrated, where the corrosion current is more than 100 times (in the case of sulfuric acid) and 17 times (in the case of hydrochloric acid) less than that of the SK-5 steel substrate. The maximum polarization resistance of So-W coatings is observed in sodium chloride and sulfuric acid environments and takes a maximum value of similar to 36000 Ohm center dot cm(2), and the minimum value of this coating shows similar to 3500 Ohm center dot cm(2) in hydrochloric acid environment.

A technology has been proposed to increase the hardness and wear resistance of M2 high-speed tool steel by combining low-temperature nitrocarburizing using anodic plasma electrolytic treatment, stepwise heating in plasma electrolysis with a change in the polarity of the workpiece, high-temperature hardening in air and triple tempering release. The structure, phase and elemental composition of the surface layers of high-speed steel after plasma electrolytic treatment with quenching, as well as subsequent tempering, were studied using the methods of x-ray, SEM and EDX analysis. Tribological tests were carried out under dry friction conditions with assessment of the friction coefficient and weight wear, as well as calculation of the microgeometry of the worn surface to assess contact stiffness and determine the wear mechanism. It has been shown that the formation of a structure of highly alloyed martensite with nitride inclusions after nitrocarburizing with quenching and the release of finely dispersed carbides during subsequent tempering leads to hardening of the surface layer to 1090-1100 HV after quenching and to 1350-1380 HV after subsequent tempering. The nitrogen concentration in the surface layer as a result of low-temperature nitrocarburizing reaches up to 13 wt.

The influence of temperature on the properties of nanocrystalline Co-W coatings obtained from a citrate electrolyte at pH 6.7 and deposited under natural convection conditions was studied. The influence of the electrolyte temperature on the morphology, composition, structure and roughness of coatings, as well as their corrosion and tribological properties, is demonstrated. It is shown that the structure of the coating can change from the X-ray amorphous to the crystalline one when the deposition temperature of the coating is increased to 90 ºС. The average value of the mass wear of Cо-W coatings formed at 80 ºС and measured under the linear friction condition of 0.08 mg, and 62 times lower than that of a Cr coating (4.95 mg) and 84 times lower that at the surface of steel SK-5 (6.71 mg). When testing by the reciprocating wear method, the value of the volumetric wear of Co-W coatings obtained in the temperature range 50–70 ºС was 0.00109 mm3, which is 55 times lower than the wear value of a Cr coating (0.0596 mm3) and 41 times lower than that of the steel SK-5 surface (0.0449 mm3). The paper also shows a slight decrease in the currents of corrosion coatings and a decrease in the dispersion values of the corrosion potentials obtained after mechanical polishing of the surface of the coatings at temperatures in the range of 20–90 ºС. It is shown that under the corrosive effect of 3.5% sodium chloride, an increase in the deposition temperature of the coating is accompanied by a slight in-crease in the corrosion current.

— The article presents the results of surface modification of austenitic stainless steel by electrolyte-plasma nitriding under anodic and cathodic polarity of the product being treated. The morphology and surface roughness, phase composition, and microhardness of diffusion layers, as well as tribological and corrosion properties, were studied. The effect of physicochemical processes during anodic and cathodic treatments on the features of the formation of a modified surface and its operational properties is demonstrated. The anodic treatment increased the hardness of the nitrided layers up to 1150 HV, halved the surface roughness, improved the wear resistance by a factor of 166, and decreased the coefficient of friction by a factor of 1.6. The cathodic treatment increased the hardness only to 580 HV and improved the wear resistance by a factor of 13.6. Both treatments were shown to decrease pitting corrosion in a sodium chloride medium.

Abstract—The possibility of using the technology of anodic plasma electrolytic carburizing in a nontoxic electrolyte to increase the microhardness and wear resistance of commercial-purity titanium is considered. The surface morphostructure and roughness the material after saturation, the microhardness distribution in the surface layer, and the tribological behavior of the modified surface are studied. Wear resistance tests are carried out under dry friction conditions using quenched tool alloy steel as a counterbody. Plasma electrolytic carburizing in an aqueous electrolyte containing ammonium chloride and glycerin is found to increase the surface hardness by 3.5 times, up to 900 HV0.01, due to the formation of a diffusion layer. The tribological behavior is influenced by high-temperature surface oxidation (leading to the formation of an outer oxide layer), the formation of a modified layer, and the surface relief of titanium. The coefficient of friction after treatment increases by 1.2 times and the mass wear decreases by 3.4 times as compared to the untreated surface of titanium parts.

The possibility of increasing wear resistance of the CP-Ti surface using a duplex surface treat-ment combining plasma electrolytic nitrocarburizing in a solution of ammonia, acetone and ammonium chloride and subsequent plasma electrolytic polishing is shown. Morphology and surface roughness, structure and microhardness of the modified layer were studied. The correla-tion of weight wear with hardness of diffusion layer at a low processing temperature and thick-ness of oxide layer is established – the largest decrease in weight wear occurs after nitrocarbu-rizing at 750 °C for 5 min (by 4.3 times). The possibility of an additional increase in wear re-sistance by subsequent polishing of the nitrocarburized CP-Ti surface at a voltage of 275–300 V for 3–5 min in chloride and fluoride electrolytes and 5–10 min in a sulfate electrolyte was re-vealed. Under these conditions, the hardened layer is preserved when the porous outer oxide layer is removed. According to the microtopology of the friction tracks, the wear mechanism is estimated as fatigue in dry friction and plastic contact.

The possibility of using the anodic electrolyte-plasma carburization technology in a non-toxic electrolyte to increase the microhardness and wear resistance of commercially pure titanium is considered. The morphostructure and roughness of the material surface after saturation were studied, the distribution of microhardness in the surface layer and the tribological behavior of the modified surface were studied. Wear resistance tests were carried out under dry friction conditions using tool alloy hardened steel as a counterbody. It has been established that electrolyte-plasma cementation in an aqueous electrolyte, containing ammonium chloride and glycerin, increases surface hardness by 3.5 times, up to 900 HV0.01, due to the formation of a diffusion layer. Tribological behavior is influenced by high-temperature oxidation of the surface, leading to the formation of an outer oxide layer, the formation of a modified layer and the titanium surface relief. The friction coefficient after treatment increases by 1.2 times, and mass wear decreases by 3.4 times compared to the untreated surface of titanium parts.

The possibility of increasing the wear resistance and corrosion resistance of the surface of low-carbon steel after cathodic plasma electrolytic boronitrocarburizing in a solution of boric acid, glycerin, and ammonium chloride, and subsequent anodic plasma electrolytic polishing in a solution of ammonium sulfate through the formation of a modified structure has been demonstrated. The modified structure consists of a dense oxide layer and a diffusion layer underneath, which contains up to 0.87

The results of modifying the surface of austenitic stainless steel by anodic plasma electrolytic treatment are presented. Surface treatment was carried out in aqueous electrolytes based on ammonium chloride (10%) with the addition of ammonia (5%) as a source of nitrogen (for nitriding), boric acid (3%) as a source of boron (for boriding) or glycerin (10%) as a carbon source (for carburizing). Morphology, surface roughness, phase composition and microhardness of the diffusion layers in addition to the tribological properties were studied. The influence of physicochemical processes during the anodic treatment of the features of the formation of the modified surface and its operational properties are shown. The study revealed the smoothing of irregularities and the reduction in surface roughness during anodic plasma electrolytic treatment due to electrochemical dissolution. An increase in the hardness of the nitrided layers to 1450 HV with a thickness of up to 20–25 μm was found due to the formation of iron nitrides and iron-chromium carbides with a 3.7-fold decrease in roughness accompanied by an increase in wear resistance by 2 orders. The carburizing of the steel surface leads to a smaller increase in hardness (up to 700 HV) but a greater thickness of the hardened layer (up to 80 μm) due to the formation of chromium carbides and a solid solution of carbon. The roughness and wear resistance of the carburized surface change are approximately the same values as after nitriding. As a result of the boriding of the austenitic stainless steel, there is no hardening of the surface, but, at the same time, there is a decrease in roughness and an increase in wear resistance on the surface. It has been established that frictional bonds in the friction process are destroyed after all types of processing as a result of the plastic displacement of the counter body material. The type of wear can be characterized as fatigue wear with boundary friction and plastic contact. The correlation of the friction coefficient with the Kragelsky–Kombalov criterion, a generalized dimensionless criterion of surface roughness, is shown.

A technology for duplex plasma treatment of the steel surface is proposed. At the first stage, it is proposed to carry out nitrocarburising at the cathode polarity of the treated sample to harden the surface layer. The composition and structure of nitrocarburised layers have been studied. It is shown that as a result of the simultaneous diffusion of nitrogen and carbon, their diffusion coefficients increase, contributing to the achievement of concentrations up to 0.74 ± 0.14

—The possibility of increasing the wear resistance of the surfaces of grade 45 steel by 19.9 times and a VT6 titanium alloy by 3.6 times after cathodic plasma electrolytic nitriding in a solution of ammonium chloride and ammonia and subsequent anodic plasma electrolytic polishing in a solution of ammonium sulfate is shown. A positive effect of decreasing the surface roughness and removing the outer part of the oxide layer by anodic plasma electrolytic polishing and increasing the hardness of the surface layer as a result of cathodic nitriding on the wear resistance has been revealed. The wear mechanism is found to be a fatigue one under plastic contact and boundary friction.

The effect of plasma electrolytic nitrocarburizing on the wear resistance of carbon tool steel in friction couples with hardened steel and lead-tin bronze is considered in order to study the mechanism and type of wear, as well as the influence of structural and morphological characteristics of the surface on them. The microgeometry of friction tracks and its change with an increasing duration of friction tests are analyzed. The equilibrium roughness is determined, which is optimal for the friction couple and ensures minimal wear. The optimal values of the plasma electrolytic nitrocarburizing parameters, which provide the lowest values of the friction coefficient and wear rate, have been determined. The phase and elemental composition of the surface layer was studied using X-ray diffraction analysis and EDX analysis. The relationship of the microstructure of the nitrocarburized layer of tool steel with the friction coefficient and weight wear is established.