Plasma Electrolytic Process Research Articles

The mechanism of evolution of microdischarges at the beginning of the PEO process on aluminum

Abstract In this study, we present the results of investigation of plasma electrolytic anodization of aluminum by means of different experimental techniques, in few first minutes of the process. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy was used to study the aluminum oxide coating morphology, microstructure and composition as well as cross-sections of the obtained coating. The mechanism of evolution of microdischarges at the beginning of the plasma electrolytic anodization process is proposed. Our results indicate that during a single discharge event, new inner oxide layer is formed at the bottom of discharge channel, between the metal substrate and the Al 2 O 3 layer. That new oxide layer and the gas that remains in the channel seem to present a higher barrier for dielectric breakdown then the original coating layer.

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.

Corrosion protection of thickness reduced plasma electrolytic layers on AZ31

In the present study plasma electrolytic oxidation of magnesium in fluoride free alkaline solution were used to form thin oxide layers with high corrosion protection. The relation between potassium hydroxide and sodium silicate was varied in the electrolyte. The plasma electrolytic process was performed as current controlled unipolar pulse technique. The microstructure of the formed layers were investigated by X‐ray diffraction and scanning electron microscopy. The electrochemical behavior was studied by linear sweep voltammetry and impedance spectroscopy. The thickness of the formed oxide layers was in the range of 1–2 µm. The surface morphology strictly depends on the electrolyte composition. Oxide layers formed in an electrolyte with the lowest relation KOH: Na2SO3 show the best performance in view of corrosion protection.

Hybrid, oxide-ceramic coatings formed on titanium alloys by PEO-EPD processes

Event Abstract Back to Event Hybrid, oxide-ceramic coatings formed on titanium alloys by PEO-EPD processes Alicja Kazek-Kesik1, Małgorzata Krok-Borkowicz2, Grzegorz Dercz3, Elżbieta Pamuła2 and Wojciech Simka1 1 Silesian University of Technology, Department of Inorganic, Analytical Chemistryand Electrochemistry, Poland 2 AGH University of Science and Technology, Department of Biomaterials, Poland 3 University of Silesia, Institute of Materials Science, Poland Introduction: Novel titanium alloys are considered as future materials to produce bone implants, thanks to their biocompatibility and corrosion resistance in body fluids. However, the titanium alloys surfaces are often modified by several electrochemical methods to enhance their bioactivity[1],[2]. Modification by anodic oxidation is relatively easy and inexpensive. It results in homogeneous oxide layer characterised by good adhesion to the substrate [3]-[5]. The surface morphology and chemical composition of the modified alloy surface may be controlled by the electrochemical parameters during plasma electrolytic process (PEO) and electrophoretic deposition (EPD). The oxide layer formed on the substrate is a conversion layer, characterized by very good adhesion and corrosion protection. EPD is usually applied to add bioactive substances, especially on the top of the material surface[6]. Materials and Methods: The hybrid coatings were formed by PEO coupled with EPD. The surfaces of Ti-15Mo (TM) and Ti-13Nb-13Zr (TNZ) alloys were anodised in suspensions of various concentrations of tricalcium phosphate (TCP, Ca3(PO4)2) in 0.1 M Ca(H2PO2)2. The PEO process was carried out at a current density of 100 and 150 mA cm-2, and voltage limit of 300 and 350 V, for TM and TNZ alloys, respectively. Various electrochemical parameters were used to determine the best conditions for the wollastonite particles deposition on the previously anodised titanium alloys surfaces. Finally, the process was carried out at 30 V during 60 or 90 min, using 5 g dm-3 suspensions of wollastonite, 25% vol. ethanol (C2H5OH); NH3 aq. was used to adjust pH of the suspensions to 10 -11. Following this, polyglycol (6 ml dm-3) was added as it acted as a dispersant to stabilize the suspension. The morphology, thickness, chemical composition, surface roughness and wettability of the coatings were examined. The cytocompability of the modified titanium alloys surface was assessed using osteoblast-like MG-63 cells. The electrochemical properties of the coatings were determined using potentiostatic measurement in Ringer solution at 37 ⁰C. The scratch-test was used to characterize adhesion of the coatings to the substrate. Results: Fig. 1. presents the representative SEM images of the coatings formed on the TM and TNZ alloy surface. Fig. 1. SEM images of the coatings formed on A) TM, and B) TNZ alloy surface. The particles of wollastonite were deposited at 30 V, during 60 min for TM, and 90 min for TNZ. TL-XRD analysis showed that the coatings were mainly composed by anatase (TiO2), tricalcium phosphate and wollastonite. The roughness of the surface was below 4 μm, and the oxide layers were hydrophilic (the water contact angle was between 50-70°). The adhesion and number of MG-63 osteoblast-like cells on the samples after 4 h, 24 h and 5 and 7 days of culture were investigated. The cells were well adhered on all of the investigated samples, and the representative images are presented in Fig. 2. Fig. 2. Fluorescence microscope images of on modified titanium alloys samples. Staining: nuclei by DAPI (blue) and cytoplasm proteins by eosin (red), bar = 100 µm. Conclusions: Various oxide-ceramic layers were formed on the titanium alloys substrates. The particles of wollastonite were deposited on the top of the TM alloy surface, but they were embedded much deeper in the oxide layer formed on the TNZ alloy. The surface modification improved the corrosion resistance of the titanium alloys in Ringers solution. Scratch testing and nanoidentation measurements showed that the coatings adhered well to the substrate. The layers were cytocompatible and promoted cell adhesion and proliferation. This work was sponsored by the Polish National Science Centre as the research project number 2013/09/N/ST5/00867.

Plasma Electrolytic Polishing – An Overview of Applied Technologies and Current Challenges to Extend the Polishable Material Range

Plasma electrolytic processes have gained attention from metal finishing industries due to their capability to considerably enhance surface properties. Especially, plasma electrolytic polishing is an innovative surface treatment resulting in very smooth, high-gloss surfaces with improved corrosion resistance. Although it has many advantages compared to electro polishing, just a few articles have been published in the field of plasma electrolytic polishing until now (mainly of stainless steel, titanium); the machining of other materials remains challenging. In this contribution, the authors provide an overview of plasma electrolytic polishing and describe new work in the field of polishing copper and its alloys. Transferring plasma electrolytic polishing to other metals and material geometries requires an adaption of the experimental conditions. To overcome this challenge a systematic methodology was developed. Several parameters, like electrolyte composition and complexing agents are investigated. Surface roughness as well as gloss was determined as function of processing time and voltage and compared to conventional electro polishing.

Modification of corrosion and tribological properties of 316L stainless steel by cathodic plasma electrolytic deposition of zirconia

Purpose – This paper aims to study the deposition of ZrO2 on 316L stainless steel surface using cathodic plasma electrolytic deposition (CPED) technique in potassium hexafluorozirconate (K2ZrF6) electrolyte solution to promote its corrosion and tribological properties. Design/methodology/approach – Plasma electrolytic oxidizing (PEO) technique is commonly used to form zirconium dioxide (ZrO2) on various substrates. But, in this paper, cathodic type of this technique (CPED) was used. Findings – Composition of the surface layer was analyzed by X-ray diffraction (XRD) and the formation of ZrO2 on the substrate was confirmed. Scanning electron microscope (SEM) was used to observe the unique morphology of the surface layer. The corrosion resistance of the coated surface was investigated by electrochemical methods involving cyclic voltammetery in Ringer’s solution. The treated sample showed a better pitting resistance. Pin-on-disk wear tests revealed that the friction coefficient of the coated sample is lower than that of the substrate. Also, it was shown that hardness and roughness of the coated sample increased after plasma electrolytic treatment. Originality/value – This paper considers the CPED of ZrO2 coating on 316L stainless steel. Some recent research works with ZrO2 coating have been prepared by PEO. There is limited or no record on the study of ZrO2 coatings by CPED process. In this study, the effort has been made to prepare a zirconia (ZrO2) coating on the stainless steel substrate through cathodic plasma electrolytic process under 200 V. Due to the excellent wear resistance, ZrO2 may be used as a high resistant and protective coating on stainless steels, which are widely used in industries and biomedical applications.

Deposition of Ni Coatings by Electrolytic Plasma Processing

Electrolytic Plasma Processing (EPP) is an emerging cleaning and coating technology capable of high deposition rates while being relatively simple and environmentally friendly. In the present study, Ni coatings were deposited via EPP on low carbon steel substrates. Initially, experiments were carried out at different processing conditions to determine their effect on the coating characteristics and select the most appropriate conditions for Ni deposition. The coated samples were characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction, and Transmission Electron Microscopy. EPP Ni depositions were conducted at the selected processing conditions for 10, 20 and 30 s. EPP produced high purity Ni coatings with an approximate grain size of 20 nm at a deposition rate of 166 nm/s. The corrosion properties were assessed in 3.5 % NaCl aqueous solution using open circuit potential measurements, potentiodynamic polarization testing and Electrochemical Impedance Spectroscopy (EIS). The microstructure and coating characteristics, both before and after corrosion testing, were studied using SEM. In spite of the short deposition time, EPP-coated Ni was shown to increase the corrosion resistance of the steel substrate by increasing the corrosion potential and significantly decreasing the corrosion rate. The EIS studies revealed that a similar corrosion mechanism prevails between pure Ni and EPP-coated Ni. Best corrosion behavior was obtained with a coating deposition time of 30 s, showing a positive shift in the corrosion potential by ~200 mV and more than an order of magnitude reduction in the corrosion rate of the low carbon steel.

The appearance of shock waves in the plasma electrolytic processing

In this paper, we have been tasked to investigate the transitional regime, to identify the main physical phenomena and give them a qualitative explanation. As a result of experimental researches, have been proposed and discussed possible mechanisms for generating shock waves in the transition region.

Modernization of clamping unit of draft of endosurgical monopolar forceps

The object of research is the plasma-electrolytic processing, namely the influence of area ratio of the anode and the cathode to the parameters of the process. Defined area ratio anode to cathode, at which the discharge burning occurs on the cathode, on the anode or on the both electrodes simultaneously. Determine the required ratio of the electrodes (S1 ≥ 2 S2) for discharge burning of the electrode S2.

Spectroscopic investigation of plasma electrolytic borocarburizing on q235 low-carbon steel

A plasma electrolytic borocarburizing process (PEB/C) in borax electrolyte with glycerin additive was employed to fabricate a hardening layer on Q235 low-carbon steel. Optical emission spectroscopy (OES) was utilized to investigate the spectroscopy characteristics of plasma discharge around the steel during PEB/C process. Some plasma parameters were calculated in terms of OES. The electron temperature and electron concentration in plasma discharge zone is about 3000–12,000K and 2×1022m−3–1.4×1023m−3. The atomic ionization degrees of iron, carbon and boron are 10−16–10−3, and 10−23–10−6, 10−19–10−4, respectively, which depend on discharge time. The surface morphology and cross-sectional microstructure of PEB/C hardening layer were observed, and the electrolyte decomposition and plasma discharge behaviors were discussed.

Investigation of the Influence of Electrolytic-Plasma Processing on Structural-Phase State and Mechanical Properties of the 40CrNiAl Alloy

It is shown that as a result of electrolytic plasma carburization is released from the solid solution carbides dispersed particles based alloy components, i.e. hardening occurs. Found that after processing the surface of the alloy samples 40CrNiAl modified form reinforced layers whose thickness depends on the time, temperature and processing of components of the electrolyte.

Corrosion and bio-tribological properties of Ti(CN)x hard coating on titanium alloy by the pulsed plasma electrolytic carbonitriding process

Ti(CN)x hard coating was deposited on Ti6Al4V alloy by the pulse plasma electrolytic carbonitriding process in formamide electrolyte. The influence of pulse frequency on the corrosion and bio-tribological properties of PEC/N coating was investigated. The results showed that higher pulse frequency (15kHz) provides a denser diffusion layer than low frequency markedly improving the corrosion resistance. The thickness and hardness of diffusion layers increase with decreasing pulse frequency and the wear resistance gets improved under dry friction. Carbonitriding layers greatly improve the bio-tribological behavior of Ti6Al4V alloy under saline and calf serum lubrication. The friction coefficient is reduced to 0.23 under calf serum lubrication and the wear rate decreases by two orders of magnitude compared with titanium alloy.

Localized Surface Modification on 1018 Low-Carbon Steel by Electrolytic Plasma Process and its Impact on Corrosion Behavior

Electrolytic plasma process (EPP) was applied on 1018 low-carbon steel sample surfaces and tested in a 3.5% NaCl solution. The treatment details of the EPP were described, and the test results indicate the improvement in corrosion rate, and localized corrosion was due to the unique surface features resulting from the EPP treatment. The corrosion protections show a sustainable consistency for EPP-treated samples in a 48 h immersion test. SEM (with FIB) and XRD were used to characterize the surface features. Potential polarization and cyclic voltammetry were performed for corrosion evaluations.

Effect of electrolyte on mechanical properties of AZ31B Mg alloy in electrolytic plasma processing

Coatings on Mg alloys were prepared using NaOH + Na2SiO3 as basic electrolyte containing electrolyte of Na2SiF6 or NaF. EPP treatment was carried out on AZ31 Mg alloys matrix under a hybrid voltage of AC of 200 V combined with DC of 260 V for 30 min. Structural and morphological analyses of ceramic coatings were analyzed by XRD and SEM. Wear and hardness of coatings were measured by pin-on disk test and Vickers hardness test. The coatings formed in Na2SiF6 and NaF electrolytes were mainly composed of MgO and Mg2SiO4. The measured micro-hardness of coating formed in Na2SiF6 electrolyte was found to be over HV 1100, while, coating formed in NaF electrolyte possessed micro-hardness of HV ∼900. These results show that the mechanical properties of AZ31B Mg alloys can be enhanced by the proper selection of electrolyte agent.

Effect of process parameters of plasma electrolytic oxidation on microstructure and corrosion properties of magnesium alloys

In this work, a plasma electrolytic oxidation process was applied to AZ91 and AM50 magnesium alloys and commercially pure magnesium to produce a protective surface layer. The plasma electrolytic oxidation process was carried out in an alkaline phosphate solution with a DC power supply, using relatively high current densities and short treatment times. The influence of some important process parameters such as current density, treatment time and voltage was studied. The layers were characterised by scansion electron microscopy, X-ray diffraction and X-ray photoelectron spectrometry, in order to investigate the effect of the process parameters on the microstructure and chemical composition. The corrosion resistance properties of the obtained layers were investigated by potentiodynamic anodic polarization and electrochemical impedance spectroscopy tests. The current density, applied during the treatment, influenced the morphology and the thickness of the coatings, and, consequently, the corrosion resistance. The corrosion tests evidenced that the layers obtained with plasma electrolytic process provided a good corrosion protection to the magnesium and magnesium alloys.

Structural-Phase Transformations in R6m5 Steel while Electrolytic-Plasma Processing

The article examines regularities of high-speed steel surface changes in the phase and structural states of during the electrolytic-plasma processing. It is determined that after modification by electrolytic-plasma influence on the surface of R6M5 high-speed steel formation of small pores, microdefects and fine inclusion. Surface modified layer consists of nitrogen austenite, nitrogen martensite and fine nitride particles.

Electrolytic plasma processing for plating coatings and treating metals and alloys

A review of the methods of electrochemical treatment classified as plasma electrolysis is given. Special attention is paid to the physicochemical processes that proceed in electrolytes and the techniques of surface modification and application of protective coatings. The results of investigation of such coatings and surfaces upon electrolytic plasma processing illustrate the efficiency and effectiveness of the method. Being an efficient technique of the surface treatment, which involves both the surface cleaning and plating the coating, the plasma-electrolytic method is being rapidly developed and adapted for commercial use at present.

Research of plasma-electrolytic processes in various ratio of the area anode to the cathode

The object of research is the plasma-electrolytic processing, namely the influence of area ratio of the anode and the cathode to the parameters of the process. Defined area ratio anode to cathode, at which the discharge burning occurs on the cathode, on the anode or on the both electrodes simultaneously. Determine the required ratio of the electrodes (S1 ≥ 2 S2) for discharge burning of the electrode S2

Investigation of the influence of plasma-electrolytic processing on the surface of austenitic chromium-nickel steels

Investigated the plasma-electrolytic processing of austenitic chromium-nickel steel. Determined that the treatment process consists of three parts: the anodic dissolution of metal anode microdischarge area burned and the area in which the combustion gas discharge – Glow vapor-gas layer around the electrode without the occurrence of certain microdischarge. The effect of processing parameters on the morphology of the surface.

Research of the impact acidity of electrolytic cathode on the course of the plasma-electrolytic process

The object of research is a gas discharge with an electrolytic cathode, namely the influence of the nature of the cathode on the discharge. Is established that with decreasing the acidity of electrolytic cathode voltage of discharge ignition decreases. A mechanism is proposed to maintain the discharge at the gas-electrolyte interface.