Plasma Electrolytic Treatment Research Articles

Plasma Electrolytic Oxidation Treatment on Magnesium Rare Earth Alloy: Effect of Low Current Density

The poor corrosion resistance of magnesium and its alloys can be overcome by developing appropriate surface treatments of these materials. The article explores the impact of using a current density of 15 mA cm−2, lower than those considered so far for the plasma electrolytic oxidation treatment of the WE43 earth rare‐based magnesium alloy, on process energy consumption as well as on microstructure and corrosion properties of oxide coatings grown on the magnesium alloy. Using a low current density during the treatment certainly means significant energy savings, but also good corrosion resistance compared to the untreated alloy, as demonstrated by electrochemical analyses and a through‐hole morphology of the oxide coating, which could be useful for all the applications in which beyond good corrosion resistance a specific surface area is essential.

Increasing the Wear and Corrosion Resistance of a CP-Ti Surface by Plasma Electrolytic Borocarburizing and Polishing

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.

Technological Methods and Equipment for Plasma-Electrolytic Processing of Metals and Alloys

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.

Self-coloring of coatings upon two-stage plasma-electrolytic treatment of AD31 alloy

Self-coloring of coatings upon two-stage plasma-electrolytic treatment of AD31 alloy

Energy characteristics of the vapor-gas shell formation stage during electrolyte-plasma treatment

The article presents the results on energy characteristics and the thermophysical state in the vapor-gas shell formation stage during electrolyte-plasma treatment. The vapor-gas shell formation stage is characterized by intense heating of the anode layer, a transition to undeveloped bubble boiling with high heat release capacity, boiling crisis emergence, and by a transition to the film mode with low heat release capacity. At the same time, a traditional electrochemical process occurs on the anode, which is accompanied by dissolving the surface layer. Dependences characterizing the influence of electrolyte-plasma treatment parameters on the specific power and specific energy of the vapor-gas shell formation stage are established. The obtained results allow optimizing the parameters of new effective processes of electrolyte-plasma treatment in controlled pulse modes, at which both electrochemical (vapor-gas shell formation) and electrolyte-plasma stages are realized within one pulse of millisecond duration.

Influence of electrophysical characteristics of plasma electrolytic treatment of 16MnCr5 structural alloy steel on structural and phase changes in the surface and its tribological properties

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 μm 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.

Features of Increasing the Wear Resistance of 90CrSi Tool Steel Surface under Various Electrophysical Parameters of Plasma Electrolytic Treatment

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.

Review of Cathode Plasma Electrolysis Treatment: Progress, Applications, and Advancements in Metal Coating Preparation.

Cathodic plasma electrolytic treatment (CPET) is an emerging surface modification and coating preparation technology. By utilizing plasma discharge induced through electrolysis and the cooling impact of electrolyte, metal cleaning, saturation, and coating preparation are efficiently achieved. In this review, the principle, application, and development of the CPET process are briefly summarized based on the past literature. Detailed insights are provided into the influence of electrolyte parameters (pH, metal salt concentration, and temperature), electrical parameters (voltage, duty cycle, and frequency), and process parameters (electrode area ratio, material, roughness, and deposition time) on plasma discharge and coating formation for metal coatings. The interaction mechanism between plasma and material surfaces is also investigated. Recommendations and future research avenues are suggested to propel CPET and its practical implementations. This review is expected to provide assistance and inspiration for researchers engaged in CPET.

Simulation of voltage characteristics of vapor-gas shell during electrolyte-plasma treatment

Electrolytic plasma processing (EPT) is a method of surface treatment of materials based on the use of plasma and an electrolytic solution. This abstract discusses the principle of action, main applications and potential benefits of EPТ. The EPТ technique involves immersing the object being treated in an electrolytic solution, after which an electric current is applied, causing decomposition of the solution and the formation of a plasma cloud at the surface of the material being processed. Exposure to plasma and chemically active components of the solution makes it possible to modify the surface of the material, improving its properties, such as adhesion, strength and corrosion resistance. EPТ is widely used in a variety of industries, including metalworking, electronics, medical equipment and food processing. The advantages of the method include high efficiency, the ability to process complex shapes and materials, as well as environmental safety due to the absence of the use of chemically aggressive substances. Electrolytic plasma processing is a promising direction in the field of surface modification of materials with a wide range of potential applications. In this paper, theoretical studies of vapor-gas shell formation in the near-surface region of structural steels in the cathodic heating mode of electrolyte-plasma treatment were considered. The technology of electrolyte-plasma hardening, providing the required mechanical properties of products, which are often subjected to wear, temperature and force effects, was investigated. Based on the results of theoretical studies, mathematical calculations of voltage, current density, and dependence graphs were made to obtain a model of vapor-gas shell formation in the process of cathodic heating. Modeling of calculations of vapor-gas shell formation in the process of cathodic heating was carried out with the help of Maple program.

Ceramic metal oxide coatings formation by hybrid plasma electrolytic treatment: Interaction scenarios of ceramic NPs with oxide layers

Understanding the formation of protective ceramic metal oxide (CMO) coatings (layers) on the surface of light alloys remains a pressing task in light of products operating in extreme conditions. Plasma electrolytic oxidation (PEO) of light alloy surfaces has recently been modified by introducing various ceramic nanoparticles (NPs) into the electrolyte to perform hybrid plasma electrolytic treatment (HPET). In this work, the general and distinctive features of the interaction mechanisms of TiC, SiO2 and ZrO2 nanoparticles (NPs) with the CMO coating formed by HPET of Al–Si and Mg-based alloys were summarized and theoretically substantiated. The interaction of charged ceramic NPs accelerated by an electric field with the oxide layer is determined by transformation of the NPs kinetic energy into heating and plastic deformation, into phase transformations, as well as into the creation of new surface defects. One of the controlling factors is the ratio of the particle and the oxide layer hardnesses. In the case of SiO2 in Al–Si alloys, the formed coating is harder than the ceramic NPs while in other cases, the NPs are harder than the CMO coating, which determines the different scenarios for the interaction of NPs with the coating under HPET. In summary 7 different scenarios for the interaction of ceramic NPs added to the electrolyte with the СМO layer during its formation put forward, which depending on the ratio of the hardness of the CMO layer and the added particles, temperature/pressure conditions of the phase transformations in the NP (including its melting), the particles size distribution and the base PEO process parameters.

АНАЛИЗ МОРФОЛОГИИ ПРИ ВОЗДЕЙСТВИИ ЭЛЕКТРОЛИТИЧЕСКОЙ СТРУИ НА ПОВЕРХНОСТЬ НЕРЖАВЕЮЩИХ СТАЛЕЙ

The article is devoted to the study of the effect of an electrolytic jet on the surface of a metal anode. The studies were carried out in the electrolysis mode with a study of the transition to the electrolyte-plasma treatment mode. Special attention is paid to the mechanisms of formation of the morphology of the surface of stainless steels 08X18H9T, AISI 301, AISI 304. It is shown that for different steels, the process of electro-chemical dissolution of the anode material is accompanied by different mechanisms of dissolution of the micronerities of the microprofile. The current-voltage characteristics of the process in the voltage range in the range of 20-250 V. The effect of the decrease in the mass of the anode material on the current value is considered. The morphology of steels has been studied under different technological conditions and at different points of contact of the electrolytic jet with the surface. The criteria accompanying the transition to the electrolyte-plasma regime from the electrolysis regime are considered.The effect of an electrolytic jet on the risks formed by mechanical treatment on the anode surface is investigated. The influence of stress on the formed surface roughness parameter Ra is considered. The calculation of the electric field strength for surface nanodefects was performed in the Comsol Multithisics program. The results of this work can be used for the development of turbine blade processing technology, electrochemical cutting and nanoobrabotation of materials.

RESEARCH OF THE CURRENT STATE AND TECHNOLOGICAL OPPORTUNITIES OF ELECTROLYTE-PLASMA CHEMICAL HEAT TREATMENT OF STEELS

In the modern world, one of the most important requirements for the production of structural steel parts in machine building is improved hardness and wear resistance. Electrolyte-plasma chemical-thermal treatment is one of the best solutions for this problem, as the surface of steel is modified while the core of the part remains in a ductile state for resistance to impact loading, and this method is resource-saving due to the saving of energy and material consumption. In the present work the questions of technological possibilities of the method of electrolyte-plasma chemical heat treatment of steels are considered. The research results of other authors have been studied, and the analysis of the influence of technological parameters on the change of structural-phase state and improvement of microhardness at electrolyteplasma chemical heat treatment has been given. Electrolyte-plasma carburizing of 20X steel was carried out at the electrolyte-plasma chemical heat treatment unit. A solution of 10% soda ash (Na2CO3), 20% urea (CH4N2O) in 70% distilled water was used as an electrolyte. It was found that the cross section of steel after electrolyte-plasma carburizing has a zonal structure, so the modified layer with a thickness of ⁓50 μm consists of α-Fe, α'-Fe, Fe3C. After electrolyte plasma treatment of 20X steel, the microhardness increased ⁓3.5 times compared to the initial state.

Taguchi Optimization of Electrolytic Plasma Hardening Process Parameters on Ti‐6Al‐4V Alloy: Microstructure and Mechanical Properties

Herein, the effects of electrolytic plasma treatment (EPT) on the hardness distribution, wear resistance, and surface morphologies of titanium alloy (Ti‐6Al‐4V) at three different thermal cycles (4‐5‐6 times) are investigated. The microstructure is controlled by heat temperature and modification times of thermal cycles depending on EPT processing parameters. A novel technique to modify Ti‐6Al‐4V alloy by the process of EPT successfully occurs. The results show that the phase transformation is shown as follows: fine α and β for the low thermal cycle → irregular martensite α′ for the high thermal cycle → complete zigzag martensite α′ for the max thermal cycle. The hardness is increased from 350 ± 10HV0.05 to 530 ± 10HV0.05 after the modification. Wear tests are conducted according to the Taguchi L9 (3^3) orthogonal array. Three parameters (load, sliding speed, and sample type) with three levels examine wear rate and coefficient of friction. Optimum levels are obtained by Taguchi analysis from the experimental results. In addition, an analysis of variance is performed to find the effectiveness of the parameters. The wear surfaces are analyzed by scanning electron microscope. After the analysis, the best result is obtained in five thermal cycles.

Possibilities of Duplex Plasma Electrolytic Treatment for Increasing the Hardness and Wear Resistance of a Commercially Pure Titanium Surface

The technology for duplex treatment of a commercially pure titanium surface is expected to increase hardness and wear resistance. This technology consists of sequential nitrocarburizing and polishing of the product in plasma electrolysis. The mechanism of duplex processing is revealed; it consists of strengthening the surface layers under diffusion saturation and controlled formation of the surface relief. The possibility of controlling the characteristics of the modified surface by combining various plasma technologies is shown. The morphological features of the surface and the surface layer after treatment were studied. The microhardness of the modified layer and the tribological properties of the surface were measured. It has been established that the samples with the highest surface layer hardness and a small thickness of the oxide layer on the surface have the highest wear resistance. After nitrocarburizing at 750 °C for 5 min, wear resistance increases by 4.3 times compared to pure material. If subsequent polishing is carried out at a voltage of 275–300 V for 3–5 min in chloride and fluoride electrolytes and 5–10 min in a sulfate electrolyte, then wear resistance can be further increased. This is achieved by removing the porous outer oxide layer.

Craniofacial reconstruction using 3D personalized implants with enhanced surface properties: Technological and clinical aspects

In this study, the modification of personalized titanium implants was developed using the plasma electrolytic oxidation process. Plasma electrolytic oxidation process parameters were initially optimized using solid samples of the Ti6Al4V alloy. Oxidation was achieved in an electrolyte containing calcium and phosphorus compounds at 250 V. The oxide layer produced was characterized by the use of human osteoblasts and fibroblasts, with high biological activity of the modified titanium alloy in relation to these cells was demonstrated. Based on tomographic examinations, models were made and then personalized implants for three patients were printed from a Ti6Al4V alloy powder. These implants were subjected to plasma electrolytic oxidation treatment within the previously developed parameters and surgically placed in the craniofacial area. On the basis of postoperative studies, surgical interventions were successful, with modification of the surface using the plasma electrolytic oxidation method producing bioactive surfaces for both bone and soft tissue.

PTFE-Containing Coating Obtained on Ti by Spraying and PEO Pretreatment

In case of using titanium alloys in equipment exposed to aggressive media (for example, sea water), it is necessary to take into account and, first of all, prevent the formation of a galvanic couple of titanium and another metal/alloy, which in most cases leads to the corrosion destruction of the latter. Another significant problem of using titanium is its low wear-resistance and poor tribological characteristics. To impart the necessary properties to titanium and its alloys, a composite coating was formed on the top of titanium. For the coating formation, a combination of the plasma electrolytic treatment and polymer spraying was used. The SEM, EDS and XRD analyses established morphological features, elemental and phase composition of the composite coatings. Contact angles and the wettability parameters of the composite coatings were investigated. An analysis of the data obtained showed that composite coatings have better protective properties than untreated material and base PEO coatings.

Enhancing compressive properties and sound absorption characteristic of open-cell Mg foams through plasma electrolytic oxidation treatment

Plasma electrolytic oxidation (PEO) technology was used to deposit a ceramic coating on the strut of open-cell Mg foams. In this experiment, the microstructure, the phase composition, and the elemental distribution of the PEO-coated Mg foams were investigated. Effect of the PEO treatment on the compressive properties and the sound absorption characteristic of open-cell Mg foams were studied. The experimental results indicate that PEO coating is mainly composed of a mixture of MgO and MgAl2O4 ceramics with high hardness and high brittleness. The compressive strength and the energy absorption capacity of Mg foams improved after being subjected to PEO treatment; however, the brittleness of the PEO-coated foams was more noticeable than that of the uncoated foams. The sound absorption coefficient of the PEO-coated Mg foams is slightly greater than that of the uncoated foams, which is mainly attributed to increased viscous friction induced by the micro-pores in the PEO coatings.

Increasing Hardness and Wear Resistance of Austenitic Stainless Steel Surface by Anodic Plasma Electrolytic Treatment

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.

Исследование плазменного электрического оксидного покрытия, сформированного на опытных образцах пластин из алюминия марки 1050

Today, the technology of hardening the surface layers of parts and the creation of protective coatings on the surface with high physical, mechanical and chemical properties are especially efficient in many industries. The article presents the studies of the most promising innovative technology for surface hardening of 1050 grade aluminum plates by plasma electrolytic oxidation method. This method allows to obtain the materials with an ultra-high melting point, high hardness, and wear resistance. Possible conditions and mechanisms for the formation of protective layers on the surface of aluminum plates to improve reliability and safety in the production of chemical industry products are considered. The influence was studied concerning the main technological parameters (alloying elements, electrical parameters, electrolyte composition) on the properties and structure of oxide ceramic coatings. The qualitative characteristics of the finished products from aluminum alloys and the surface layer of the samples showed the efficiency of the plasma electrolytic oxidation technology, which allows to obtain ceramic coatings with increased hardness, wear and corrosion resistance, and strength. When processing by plasma electrolytic oxidation in an aqueous electrolyte solution, all the industrial safety requirements are met. An alternative approach to processing by plasma electrolytic oxidation is considered, in which 1050 grade aluminum plates were used in a molten nitrate salt at a temperature of 280 °C. The microstructure, phase, chemical composition, and microhardness were studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness tests. The formed coating was found to be free from electrolyte contamination, cracks and pinholes commonly found in coatings formed during plasma electrolytic oxidation treatment in an aqueous electrolyte solution.

Plasma Electrolytic Oxidation Treatment of AZ31 Magnesium Alloy for Biomedical Applications: The Influence of Applied Current on Corrosion Resistance and Surface Characteristics

Magnesium alloys are an exciting challenge for the biomaterials field given their well-established biodegradability and biocompatibility. However, when exposed to biological fluids, their rapid degradation and hydrogen release are the main drawbacks for clinical applications. This work aimed to investigate the influence of the current density applied during the plasma electrolytic oxidation (PEO) treatment on the durability of an AZ31 magnesium alloy. In particular, specific interest was directed to the degradation rate undergone by the PEO coating, obtained under two different current density conditions, when exposed to Hank’s solution at 37 °C to simulate the physiological environment, employing the techniques of potentiodynamic polarization and electrochemical impedance spectroscopy. Experimental results highlighted that the plasma electrolytic oxidation technique resulted in an improvement in the corrosion resistance of the magnesium alloy in the test solution. The current density affected the morphology of the coating. In particular, the anodic oxide coating obtained by applying the highest current density showed a higher thickness and fewer but larger pores, while the lowest current density generated a thinner PEO coating characterized by several but smaller pores. Surprisingly, the best corrosion resistance has been exhibited by the anodic oxide coating grown at the highest current density.