Plasma Electrolytic Treatment Research Articles

Investigation of the effect of a low-temperature plasma of vapor–gas discharges with the use of electrolytic electrodes at lower pressure on products of complex shape

The effects of mechanical, electrochemical, laser, and electrolytic plasma treatment on the morphology and grade of finish of the outside and face surfaces of stator rings made of electrical steel are investigated with the use of X-ray diffraction analysis.

Raising the Corrosion Resistance of Low-Carbon Steels by Electrolytic-Plasma Saturation with Nitrogen and Carbon

Structural features of the external oxide layer and internal nitrided, carbonitrided and carburized layers in steels 10, 20 and St3 produced by the method of electrolytic plasma treatment are studied. Specimens of the steels are tested for corrosion in a naturally aerated 1-N solution of sodium chloride. The condition of the metal/sodium chloride solution interface is studied by the method of electrochemical impedance spectroscopy. It is shown that the corrosion resistance of low-carbon steels can be raised by anode electrolytic-plasma saturation with nitrogen and carbon. Recommendations are given on the choice of carbonitriding modes for structural steels.

Changes in mechanical properties and structure of electrolytic plasma treated × 12 CrNi 18 10 Ti stainless steel

Abstract The paper addresses findings regarding the influence of electrolytic plasma treatment on the mechanical properties as well as structural and phase states of × 12 CrNi 18 10 Ti steel. Electrolytic plasma treatment is based on carburizing of stainless steel heated in electrolytes. Treatment of steel samples has been performed as follows: the samples were heated up to a temperature between 850 and 950 °C and then they were cured for 7 minutes in an electrolyte of an aqueous solution containing 10 % glycerol (C3H8O3) and 15 % sodium carbonate (Na2CO3). It is found that, after plasma electrolytic treatment, the surface of × 12 CrNi 18 10 Ti steel had a modified structure and high hardness. Increasing wear resistance of × 12 CrNi 18 10 Ti steel has been observed after carburizing and the coefficient of friction has been reduced. X-ray analysis showed that retained austenite γ-Fe is a main phase, and there are some diffraction lines of orthorhombic Fe3C phase as well as Fe3O4 cubic phase. It has been de...

Influence of process parameters on plasma electrolytic surface treatment of tantalum for biomedical applications

This work aims to quantify the effect of anodization voltage and electrolyte composition used during DC plasma electrolytic oxidation (PEO), operated as a 2-step process, on the surface properties of the resulting oxide coatings on tantalum. The first step consisted of galvanostatic anodization (150mAcm−2) of the tantalum workpiece up to several limiting voltages (200, 300, 400 and 500V). After attaining the limiting voltage, the process was switched to voltage control, which resulted in a gradual decrease of the anodic current density. The anodic treatment was realized in a 0.5M Ca(H2PO2)2 solution, which was then modified by the addition of 1.15M Ca(HCOO)2 as well as 1.15M and 1.5M Mg(CH3COO)2. The increasing voltage of anodization led to the formation of thicker coatings, with larger pores and enriched with electrolytes species to a higher extent. The solutions containing HCOO− and CH3COO− ions caused the formation of coatings which were slightly hydrophobic (high contact angle). In the case of the samples anodized up to 500V, scattered crystalline deposits were observed. Bioactive phases, such as hydroxyapatite, were detected in the treated oxide coatings by XRD and XPS.

Plasma electrolytic treatment of VT22 titanium alloy in electrolytes with carbon-containing compounds

The study investigates the influence of electrolyte compositions containing acetone, glycerol, sucrose, ethylene glycol and ammonium chloride on the properties of VT22 titanium alloy in the process of the anode plasma electrolytic treatment (PET). An X-ray diffractometer and a scanning electron microscopy (SEM) were used to characterize the phase composition and morphology of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a pin-on-disc tribometer under lubricated testing conditions. The effect of electrolyte compositions on the corrosion resistance of the PET samples was examined by means of potentiodynamic polarization in a solution of Na2SO4. It was assumed that the PET provides the saturation of titanium alloy with oxygen and carbon and formation TiO2 with a rutile structure and carbon solid solution in titanium. The anode PET in an electrolyte with glycerol results in an increase in microhardness to 540 HV and a decrease in the corrosion current density by 2.4 times. The friction coefficient of the treated samples in anelectrolyte with sucrose can be reduced 7.5 times. The anode PET in all electrolytes enables todiminish the wear rate of the titanium alloy samples by 3 orders of magnitude and the surface roughness, too, due to the anode dissolution of titanium.

Thermal features of plasma electrolytic heating of titanium

The study considers heat exchange relations in terms of anode plasma-electrolytic treatment of titanium. The density of heat fluxes from vapour-gas envelope (VGE) to the anode-sample, electrolyte and atmosphere are experimentally determined. A model of heating temperature calculation considering heat transfer to the atmosphere along the cross-section of the workpiece is developed. Interrelations between envelope thickness and voltage as well as temperature-voltage characteristic (TVC) of the process are found. It is established that, other conditions being equal, anode heating of titanium is characterized by higher temperature at lower values of current and density of the heat flux from the vapor-gas envelope, compared with treatment of steel workpieces. The resulting dependences are confirmed by numerical evaluation with the use of the developed model and are explained by lower specific heat conductivity of titanium, contributing to a decrease of heat transfer from the heated part of the sample to the part protruding over electrolyte surface. The heat flux from the envelope to the electrolyte is found to be determined by power input in the system and independent of the anode material.

Plasma-Electrolytic Treatment as an Innovative and Resource-Saving Technology of Metal Surface Treatment

The research presents the capabilities of the method of plasma-electrolytic treatment of metal surface that define it as an innovative and resource-saving technology. It is characterized by the synergetic effect of the plasma-electrolytic technology on the surface being treated. The paper shows the effect of different plasma-electrolytic treatment conditions on change of metal physico-chemical and structural-energy properties.

Wettability and electrochemical properties of the highly hydrophobic coatings on PEO-pretreated aluminum alloy

Abstract Morphology, composition, and barrier properties of superhydrophobic (SHP) coatings on the surface of AMg3 aluminum alloy pretreated by plasma electrolytic oxidation (PEO) have been investigated. Results of the study of hydrophobic layers on aluminum alloy, which underwent plasma electrolytic oxidation (PEO) and additional treatment under UV-radiation in the presence of ozone plasma with subsequent deposition of the hydrophobic agent (methoxy-{3-[(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl)oxy]propyl}-silane solution in decane), have been described. Coatings formed by deposition of dispersion of the hydrophobic agent containing SiO 2 nanoparticles on the surface of the PEO-layer are characterized by high contact angles and inhibitive properties. The formed composite layers were found to be characterized with hydrophobicity (contact angle higher than 157°) and high barrier properties (the impedance modulus, | Z | f = 0.01 Hz , ranges from 9.2 × 10 9 to 1.1 × 10 11 Ω cm 2 depending on the treatment procedure).

Effect of plasma electrolytic oxidation treatment on the mechanical properties of a Zr–Cu–Ni–Ti–Al bulk metallic glass

In this study, the effect of plasma electrolytic oxidation (PEO) treatment on the mechanical properties of a Zr52.5Cu25Ni9.5Ti6Al7 BMG was investigated by compression test. It was found that the PEO treatment can improve the room-temperature plasticity. After 30min treatment, the plastic strain of BMG increases from 2.5% to 6.2%. The results indicated that the in-situ formed PEO coating can not only act as physical constraint to consume the kinetic energy of the propagating shear band, but also can introduce nucleation sites for shear bands due to stress concentration and compositional inhomogeneity. The present results provide a promising method to enhance the plasticity of BMGs through surface PEO treatment.

Increase in Corrosion Resistance of Commercial Pure Titanium by Anode Plasma Electrolytic Nitriding

Features of the anode electrolytic plasma processing of commercial pure titanium and its alloys in aqueous solutions of ammonium chloride and ammonia additives are studied. It is identified that structure of modified layer contains an external TiO2 or TiO layer with micropores of up to 100 nm and a diffusion sub-layer after nitriding in the solution with the ammonia addition. Some increase in the surface microhardness is found. The plasma electrolytic treatment of titanium makes it possible to enhance its corrosion resistance by short-term (5 min) saturation with nitrogen at 750 °C in an electrolyte containing 5% ammonia and 10% ammonium chloride. The oxide coating formed during the anodic treatment has a positive effect on the corrosion resistance of titanium and results in reduce of the corrosion rate by two orders under continuous tests. Saturation of titanium samples with nitrogen leads to an increase in their strength properties after corrosion tests with a slight decrease in ductility. An additional advantage of this coating is to reduce of leaching of alloying elements from samples in corrosive environments.

ELECTROLYTIC-PLASMA TREATMENT OF INNER SURFACE OF TUBULAR PRODUCTS

While manufacturing a number of important tubular products stringent requirements have been imposed on quality of their inner surfaces. The well-known methods for inner surface treatment of pipes include sandblasting, chemical cleaning with acid reagents (oxalic, formic, sulfamic, orthophosphoric acids) and electrochemical polishing. Disadvantages of the chemical method are cleaning-up irregularities, high metal removal, limited number of reagent application, complicated selection of reagent chemical composition and concentration, complicated and environmentally harmful recycling of waste chemicals, high cost of reagents. Low productivity at a high cost, as well as hazardous impact on personnel due to high dispersion of abrasive dust are considered as disadvantages of sandblasting. Electrochemical polishing is characterized by the following disadvantages: low processing productivity because supply of high currents is rather difficult due to electrolyte scattering capacity away from the main electrode action zone, limited length of the cavity to be treated due to heating of flexible current leads at operating current densities, application of expensive aggressive electrolytes and high costs of their recycling. A new method for polishing and cleaning of inner surfaces of tubular products based on electrolyte-plasma treatment has been developed. In comparison with the existing methods the proposed methods ensures quality processing with high intensity while applying non-toxic, environmentally friendly and cheap electrolytes. The paper presents results of investigations on technological specific features of electrolyte-plasma treatment for inner surfaces of tubular products: influence of slotted nozzle width, electrolyte flow and rate on stability of gas-vapor blanket, current density and productivity. Results of the research have made it possible to determine modes that provide stability and high productivity in the process of electrolyte-plasma treatment of inner surfaces of tubular products.

Quality of Turbine Blades after Electrolytic Plasma Removal of an Aluminide Coating

Dimensional and shape errors of nickel-alloy components after electrolytic plasma treatment are considered.

Plasma electrolytic treatment of products after selective laser melting

The aim of the work was to study the possibilities of plasma electrolytic treatment for cleaning surfaces of metal products obtained by the SLM-technology. We found that the most effective cleaning from the large alloy particles occurs in the "hydrodynamic" mode, when the occurrence of hydrodynamic pulses observed. Further smoothing of irregularities eliminated by a stable burning of discharge in vapor shell. Analysis the morphology of the surface of difficult specialized products, such as crown conical gears, after plasma hydrodynamic treatment showed efficiency and advantages in comparison to conventional methods of final cleaning such as shot blasting.

Wear-resistant black decorative coating produced by the plasma electrolytic oxidation method on titanium alloys

The study determines the technological mode of plasma electrolytic treatment (PET) processes for the VT6 (Ti-6Al-4V) and VT1-0 titanium alloys allowing to obtain SiO2-based amorphous black decorative coatings on their surfaces at high speed (>5 μm/min at 10 A/dm2 AC density). The coating applied to the VT6 alloy increases its wear resistance more than twice. The mechanism of black decorative coating formation on titanium alloys is proposed. It is based on the obsidian formation due to rapid solidification of the SiO2 melt and the penetration of small vanadium oxide amounts into the amorphous SiO2-based coating. While decorative black coating on the VT6 alloy is obtained due to the presence of vanadium oxide (4,3 %) in the obsidian-based coating, in order to create the coating of the same decorative colour on the VT1-0 alloy it is necessary to introduce sodium vanadate into aqueous solution during the plasma electrolytic treatment.

Changes of thermal balance in a plasma-electrolyte system according to the shape of the applied voltage

The work is aimed at studying the changes of the heat balance in the system of the electrode-plasma-gas / vapor-electrolyte in various forms of applied voltage. It was established that in contrast to the voltage, which is obtained after full-wave rectification, film boiling occurs by using a smoothing capacitive filter. This is because in the pulsing mode voltage value has zero value at the beginning and end of the pulse, also at that time takes place cooling of the electrode at the contact with the electrolyte. In this paper describes a heat exchange in two different modes of plasma-electrolytic treatment.

Effect of plasma electrolytic oxidation treatment on corrosion behavior of closed-cell Al-A356 alloy foam

Closed-cell Al-A356 alloy foam was produced via casting practice. Surface of the foams were treated by plasma electrolytic oxidation (PEO) process using different electrical currents of 2.5, 5 and 10A. The produced oxide layers consisted of aluminum and silicon elements that reduced the corrosion rate of the foam in 3wt% NaCl solution. Results revealed that the 10A-PEO treated sample provided the optimum coating on the closed-cell aluminum foam, due to formation of a barrier layer and a less-cracked porous surface, also corrosion rate of the PEO treated foam was ∼2% of the uncoated one.

Effects of duty cycle and electrolyte concentration on the microstructure and biocompatibility of plasma electrolytic oxidation treatment on zirconium metal

Recently, the plasma electrolytic oxidation (PEO) process has been widely studied and applied in the industrial setting due to its ability to create functional oxide layers on Al, Ti, Mg, and Zr alloys. In this work, a pulsed direct current (DC) power supply was adopted to grow the zirconia coating on pure Zr metal by PEO treatment. A fixed frequency of 1000Hz and constant current of 2A were used to fabricate all zirconia coatings. Duty cycle values of 25%, 75%, and 100% were used and 0.1M K3PO4 aqueous solution containing three different concentrations of KOH, 0.01, 0.05 and 0.1M, was also used in fabrication. The plasma breakdown voltage decreased with increasing KOH concentration due to its higher electrolyte conductivity. The PEO oxide coating consisted of a thin continuous barrier layer and a thick porous outermost layer, which consisted of mainly monoclinic and minor tetragonal ZrO2 phases. The PEO treatment of Zr metal provided excellent corrosion resistance in Hank's solution and good biocompatibility for 3T3 and MG63 cells. These results suggest that PEO coatings having potential applications in the biomedical field were confirmed in this study.

Formation of Composite Coatings Using Fluoropolymer Materials

Surface modification of magnesium alloys by plasma electrolytic oxidation (PEO) and subsequent treatment with suspension of superdispersed polytetrafluoroethylene and tetrafluoroethylene telomeric solution are presented. Electrochemical, mechanical properties and wettability of obtained composite coatings were investigated. The polymer-containing coatings decrease the corrosion current and wear by orders of magnitude as compared to unprotected magnesium alloy and base PEO-coatings.

Evaluation of Electrochemical Properties of the PEO-Coatings Treated with Hydrophobic Agent Solution on Aluminium Alloy

The developed methods of formation and results of the study of the hydrophobic layers on aluminum alloy, previously subjected to plasma electrolytic oxidation (PEO) and additional treatment (either in ethanol solution or under UV-radiation in the presence of ozone plasma) with subsequent deposition of the hydrophobic agent (methoxy-{3-[(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl) oxy] propyl}-silane solution in decane) have been described. It was found, that the formed composite layers possess a hydrophobicity (contact angle higher 157o) and high anticorrosion properties (the impedance modulus, |Z|f=0.01Hz, ranges from 9.2·109 to 4.0·1010 Оhm·cm2 depending on the treatment procedure).

Insights into plasma electrolytic oxidation treatment with particle addition

Plasma electrolytic oxidation (PEO) processing has received considerable attention for improving the corrosion or wear resistance of magnesium and its alloys. However, it cannot provide high-barrier long-term protection due to its high porosity. A novel approach is to introduce reactive particles to PEO coatings, aiming to seal the porosity and to provide wider range of coating compositions. Experiments with nano- and micro-sized SiO2 particles and different concentrations of KOH in the electrolyte provide new insights into possible up-take and incorporation mechanisms of particles during PEO processing.