Plasma Electrolytic Oxidation Research Articles

The Influence of the Plasma Electrolytic Oxidation Parameters of the Mg-AZ31B Alloy on the Micromechanical and Sclerometric Properties of Oxide Coatings

This manuscript presents the influence of manufacturing process parameters (peak current density, frequency, process time) on the micromechanical and sclerometric properties of oxide coatings. These parameters were selected based on Hartley’s experimental design, considering three variables at three levels. The coatings were produced on the AZ31B magnesium alloy using the plasma electrolytic oxidation (PEO) method. A trapezoidal voltage waveform and an alkaline, two-component electrolyte were used during the process. The micromechanical and sclerometric properties were assessed by measuring the hardness (HIT) and Young’s modulus (EIT) and determining three critical loads: Lc1 (the critical load at which the first coating damage occurred—Hertz tensile cracks within the scratch), Lc2 (the critical load causing the first cohesive damage to the coating), and Lc3 (the load at which the coating was completely destroyed). Scratch tests were supplemented with profilographometric measurements, which were used to generate isometric images. To identify the relationship between micromechanical and sclerometric properties and the manufacturing parameters, statistical analysis was performed. Research has demonstrated that the plasma electrolytic oxidation (PEO) process improves the micromechanical and adhesive properties of oxide coatings on the AZ31B magnesium alloy. The key process parameters, including peak current density, frequency, and duration, are crucial in determining these enhanced properties.

Advancements in surface treatments for aluminum alloys in sports equipment

Abstract This review examines recent advancements in surface treatment technologies for aluminum alloys used in sports equipment. We discuss conventional methods like chemical conversion coatings and anodizing, as well as emerging techniques such as plasma electrolytic oxidation, physical vapor deposition, and laser surface modification. The replacement of toxic hexavalent chromium with eco-friendly alternatives is highlighted as a key development. We also explore the potential of smart, self-healing coatings to extend equipment lifespan. Our analysis reveals that while significant progress has been made in enhancing corrosion resistance and mechanical properties, challenges remain in scaling up advanced treatments for industrial implementation. The review concludes that continued innovation in surface treatments will be crucial for improving the performance, safety, and sustainability of aluminum alloys in sports applications, ultimately benefiting athletes and manufacturers alike.

Hierarchically Structured Ceramic Coatings Based on Zirconia and Magnesium Oxide with High Toughness

AbstractA major challenge in the application of ceramic materials is a trade‐off between strength and toughness. In this work, hierarchically structured ceramic coatings (HSCCs) are fabricated to address this challenge. HSCCs feature a dual‐layer micron‐scale structure built on a “brick‐mortar” nanoscale structure, which is achieved by changing the crystalline and amorphous phase ratio during plasma electrolytic oxidation (PEO). It is found that HSCCs with homogeneous interfaces exhibit high thermal stability up to 700 °C and a 65% improvement in shear strain resistance compared to conventional crystalline coatings (CCCs). This improvement is attributed to the stabilizing effect of atoms on the boundaries of the enhancement phase and the facilitating effect on the deformation of the compliant phase. The hierarchical structure effectively leverages the plasticity of the compliant phase and the strength of the enhancement phase facilitated by the homogeneous interface. This work proposes a feasible approach for improving the toughness of ceramic functional composites and mitigating their susceptibility to brittle fracture.

Study on the Thermal Control Performance of Mg-Li Alloy Micro-Arc Oxidation Coating in High-Temperature Environments

This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), UV–visible near-infrared spectroscopy (UV-VIS-NIR) and infrared emissivity measurements. The results indicate that the hemispherical emissivity of the coating remains unaffected with an increase in temperature and holding time, while the solar absorption ratio gradually increases. The thermal control performance of the coating after a high-temperature experiment was found to be related to the diffusion of the Li metal element in the magnesium lithium alloy matrix, as determined by X-ray photoelectron spectroscopy (XPS), flame graphite furnace atomic absorption spectrometry (GFAAS) and Glow Discharge Optical Emission Spectroscopy (GD-OES). As the holding time is extended, the coating structure gradually loosens under thermal stress. The Li metal element in the substrate diffuses outward and reacts with O2, H2O and CO2 in the air, forming LiO2, LiOH, Li2CO3 and other products. This reaction affects the coating’s solar absorption ratio in the end.

Tribological Properties of 7A04 Aluminum Alloy Enhanced by Ceramic Coating

The 7A04 Al alloy is a commonly used lightweight metal material; however, its low wear resistance limits its application. In this study, the wear resistance of this alloy was improved by preparing micro-arc oxidation (MAO) coatings, MAO/MoS2 composite coatings, and hard-anodized (HA) coatings on its surface. The friction and wear behaviors of these three coatings with diamond-like coated (DLC) rings under oil lubrication conditions were investigated using a ring–block friction tester. The wear rates of the coatings on the block surfaces were determined using laser confocal microscopy, and the wear trajectories of the coatings were examined using scanning electron microscopy. The results indicated that, among the three coatings, the MAO/MoS2 coating had the lowest coefficient of friction of 0.059, whereas the HA coating had the lowest wear rate of 1.47 × 10−6 mm/Nm. The MAO/MoS2 coatings exhibited excellent antifriction properties compared to the other coatings, whereas the HA coatings exhibited excellent anti-wear properties. The porous structure of the MAO coatings stored lubricant and replenished the lubrication film under oil lubrication. Meanwhile, the introduced MoS2 enhanced the densification of the coating and functioned as a solid lubricant. The HA coating exhibited good wear resistance owing to the dense structure of the amorphous-phase aluminum oxide. The mechanisms of abrasive and adhesive wear of the coatings under oil lubrication conditions and the optimization of the tribological properties by the solid–liquid synergistic lubrication effect were investigated. This study provides an effective method for the surface modification of Al alloys with potential applications in the aerospace and automotive industries.

Fabrication and Characterization of Micro-Arc Oxidation Films on β-Titanium Alloy in Silicate and Silicate/Glycerin Electrolyte

Micro-arc oxidation (MAO) films were fabricated on the Ti-39Nb-6Zr alloy at different voltages in the silicate and silicate/glycerin electrolyte. Their morphology, phase structure and composition were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the glycerin additive in the silicate electrolyte improved the compactness of the MAO film. The corrosion resistance was evaluated, and the influence of glycerin additive in electrolyte on the growth of micro-arc oxidized film was revealed by optical emission spectra.

Review of Electrical Parameters Influence on Characteristics of Plasma Electrolytic Oxide Coating on Zircaloy

<p>Zircaloy-4 (Zr-4) is used as a fuel cladding material in Pressurized Water Reactor (PWR). Zr-4 as a cladding material works in extreme conditions in pressurized water up to 150 atm at 325 ˚C. In addition, the refuelling process in the reactor requires surface protection of the clay material to minimize corrosion and wear. One of the raising methods to enhance the corrosion resistance of the Zr-4 is by plasma electrolytic oxidation (PEO). Characteristics of the ceramic oxide layer produced by PEO are influenced by current density, type and composition of the electrolyte, and voltage mode. One of the challenges in the PEO development on the Zr-4 substrate is a high porosity with a range of 5%-20% and the low number (below 6%) of t-ZrO<sub>2</sub> phases in the inner and outer layers. Optimizing the electrical parameters is necessary to overcome this problem. The results of the literature study show that the cathodic current at the AC voltage plays an important role in determining the resulting plasma characteristics. Low duty cycle (cathodic current> 50%) produce plasma with high density, resulting in a low porosity layer. Oppositely, high duty cycle (cathodic current <50%) produced high content of t-ZrO<sub>2</sub> increase the mechanical resistance. Two-step PEO is beneficial in combining the low and high duty cycle to obtain the benefit of each step. </p>

Literature Review−Effect of Additives and Post-Treatments on Corrosion Resistance and Mechanical Properties of Plasma Electrolytic Oxidation Products in Magnesium and Titanium

<p class="Abstract">Plasma Electrolytic Oxidation (PEO) is a method of converting metal surfaces into an oxide layer with the help of plasma to improve the surface mechanical properties and corrosion resistance of metals. A PEO layer of about 10-50 μm is obtained quickly from 1 second-10 minutes at a voltage range of 150-500 V with AC or DC mode. Characteristics of the outer layer of PEO have pores and cracks, while the inner layer is relatively denser. Cracks and pores reduce the corrosion resistance and mechanical properties of the coating. In this study, a literature search was carried out on the effect of adding additives and post-treatment on the characteristics of PEO coatings grown on magnesium (Mg) and titanium (Ti) metals for biomedical applications. Mg and Ti metals have opposite chemical properties; Mg is a reactive metal, while Ti is an inert metal. Comparing the behavior of the PEO process and the coating produced by the two different metals is absorbing and necessary to understand the fundamentals of the PEO process. The results of a literature search show that the addition of additives increases the growth rate of the coating so that the coating is thicker and more wear resistant. The hardness of the coating also increases due to the additive particles trapped in the oxide layer filling the micro pores so that the surface becomes denser and more homogeneous. Therefore, corrosion resistance also increases, as indicated by a decrease in corrosion current as measured by the polarization test and an increase in the impedance modulus as measured by the electrochemical impedance test (EIS). The post-alkali treatment allows for increased surface bioactivity, as indicated by the rise in the Ca/P ratio after immersion in a physiological solution.</p>

Bioresorbable composites based on magnesium and hydroxyapatite for use in bone tissue engineering: focus on controlling and minimizing corrosion activity

A biodegradable matrix with a significant content of bioactive components can be applied for bone tissue replacement, including load-bearing applications in orthopedic surgery. The study outlines the optimized procedure for the production of bioresorbable magnesium-hydroxyapatite (Mg-HA) composites and their corrosion resistance properties. Composites were meticulously crafted by combining pure magnesium with microwave-synthesized hydroxyapatite nanopowder. Sintering occurred via spark plasma sintering technology (SPS). To align the degradation time of the resulting composites with bone remodeling, the corrosion resistance of SPS materials was enhanced through the application of plasma electrolytic oxidation (PEO) and polycaprolactone (PCL) spin-coating methods. The protective properties, morphology dynamics, and composition due to surface treatment and corrosion propagation were investigated using Electrochemical Impedance Spectroscopy (EIS), Potentiodynamic Polarization (PDP), hydrogen evolution tests, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray (EDX) as well as X-ray diffraction (XRD) analysis. Analytics of the physicochemical properties data of the formed coatings indicate a significant improvement in protective characteristics and deceleration of the corrosive degradation of the samples. The application of polycaprolactone to the PEO coating leads to a decrease in the corrosion current compared to uncoated magnesium composites by more than three orders of magnitude: from 1 10-5 to 2 10-9 A cm-2. During long-term exposure of samples to 0.9 % NaCl solution, it was found that coating reduced the rate of corrosion degradation of samples from 1.5 to 80 times compared to an unprotected Mg-HA composite and sintered magnesium. Mg-HA composites treated with PEO exhibit potential application as bioactive and biodegradable materials for orthopedic implants and fixation devices.

Incorporation of Cerium Oxide Nanoparticles into the Micro-arc Oxidation Layer Promotes Bone Formation and Achieves Structural Integrity in Magnesium Orthopedic Implants

Biodegradable metals offer significant advantages by reducing the need for additional surgeries following bone fixation. These materials, with their optimal mechanical and degradable properties, also mitigate stress-shielding effects while promoting biological processes essential for healing. This study investigated the in vitro and in vivo biocompatibility of ZK60 magnesium alloy coated with a micro-arc oxidative layer incorporated with cerium oxide nanoparticles in orthopedic implants. The results demonstrated that the magnesium substrate undergoes gradual degradation, effectively eliminating long-term inflammation during bone formation. The micro-arc oxidative coating forms a dense ceramic layer, acting as a protective barrier that reduces corrosion rates and enhances the biocompatibility of the magnesium substrate. The incorporation of cerium oxide nanoparticles improves the tribological properties of the coating, refining degradation patterns and improving osteogenic characteristics. Furthermore, cerium oxide nanoparticles enhance bone reconstruction by facilitating appropriate interconnections between newly formed bone and native bone tissue. Consequently, cerium oxide nanoparticles contribute to favorable biosafety outcomes and exceptional bone remodeling capabilities by supporting bone healing and sustaining a prolonged degradation process, ultimately achieving dynamic equilibrium in bone tissue formation. Statement of SignificanceThis study comprehensively examined the incorporation of ceria nanoparticles into biodegradable magnesium through a micro-arc oxidative process for use in orthopedic implants. This study conducted a comprehensive analysis involving material characterization, biodegradability testing, in vitro osteogenesis assays, and in vivo implantation, highlighting the potential benefits of the distinctive properties of ceria nanoparticles. This research emphasizes the ability of ceria nanoparticles to enhance the biodegradability of magnesium and facilitate remarkable bone regeneration, suggesting promising advantages for additive materials in orthopedic implants.

Corrigendum to: “Recent Patents of Micro-arc Oxidation Technology”

A typographical error appeared in terms of repetition of sentences in the manuscript titled “Recent Patents of Micro-arc Oxidation Technology”, 2024; 18(6): e300423216386 [1]. <p> Original: Liu et al. [90] provided a method for micro-arc oxidation of electrolytes and reducing the brittleness of microporous ceramic film. By adding chitin nanowhiskers and Nacetylated chitosan into the electrolyte, the toughness of the ceramic film is improved, and bending brittleness and fragmentation are prevented. <p> Li et al. [91] provided an electrolyte for micro arc oxidation self-lubricating composite ceramic coating. The friction and wear properties of the composite ceramic coating were improved by adding nano additives and micro MoS2 powder into the conventional electrolyte. <p> Liu et al. [90] provided a method for micro-arc oxidation of electrolytes and reducing the brittleness of microporous ceramic film. By adding chitin nanowhiskers and Nacetylated chitosan into the electrolyte, the toughness of the ceramic film is improved, and bending brittleness and fragmentation are prevented. <p> Li et al. [91] provided an electrolyte for micro arc oxidation self-lubricating composite ceramic coating. The friction and wear properties of the composite ceramic coating were improved by adding nano additives and micro MoS2 powder into the conventional electrolyte. <p> Corrected: Liu et al. [90] provided a method for micro-arc oxidation of electrolytes and reducing the brittleness of microporous ceramic film. By adding chitin nanowhiskers and Nacetylated chitosan into the electrolyte, the toughness of the ceramic film is improved, and bending brittleness and fragmentation are prevented. <p> Li et al. [91] provided an electrolyte for micro arc oxidation self-lubricating composite ceramic coating. The friction and wear properties of the composite ceramic coating were improved by adding nano additives and micro MoS2 powder into the conventional electrolyte. <p> The original article can be found online at https://www.eurekaselect.com/article/131347

Effects of ultrasonic treatment and current pulse frequency on properties of micro-arc oxidation coating on Mg alloy LAZ931

To enhance corrosion resistance of magnesium-lithium (Mg-Li) alloy LAZ931 in corrosive environments, a micro-arc oxidation (MAO) based surface treatment was carried out under a unipolar pulsed power supply. Effects of ultrasonic treatment and current pulse frequency on the performance of MAO coatings were investigated using scanning electron microscopy, electrochemical characterization, and friction wear tests. Results demonstrate that ultrasonic treatment greatly reduced the number density of micro-defects in the resulting MAO coatings and improved their overall performance. Corrosion and wear resistance of the MAO coating increased when current pulse frequency increased from 400 to 2000 Hz. Those findings are beneficial for improving the performance of MAO on Mg-Li alloys through optimizing the processing parameters.

Antibacterial and biological properties of MAO treated Mg-Bi alloys

The clinical application of Mg implant is limited due to the poor corrosion resistance, antibacterial and biological properties. In our previous work, Mg-Bi alloy with micro-arc oxidation (MAO) treatment was prepared and proved to have good corrosion resistance, so in this work, their antibacterial property and bioactivity were also investigated to evaluate its potential application in clinics. The results showed that, the Mg-Bi alloy has good antibacterial performance, and with the increase of Bi content, the antibacterial property was enhanced. After MAO treatment, the antibacterial performance was slightly decreased, however the MAO-Mg-6Bi and MAO-Mg-9Bi still showed excellent antibacterial property, additionally, they can also induce apatite formation in simulated body fluid (SBF), indicating improved bioactivity. Based on the good comprehensive properties, the MAO treated Mg-Bi alloy has a great potential to be used as an implant material in clinics.

Microstructure characterization and corrosion performance of an AlMgScZr selective laser-melted component prepared via plasma electrolytic oxidation: effect of processing time

Microstructure characterization and corrosion performance of an AlMgScZr selective laser-melted component prepared via plasma electrolytic oxidation: effect of processing time

Effect of NaOH etching and oxygen plasma treatments on surface characteristics and their potential to activate micro-arc oxidized TiO2 coatings

Activation treatments such as NaOH etching or O2 plasma can play an essential role in surface conjugation of titanium with biomolecules, providing a better interaction at the bone-implant interface. However, their application on complex titanium dioxide (TiO2) surfaces is still not explored. In this contribution, bioactive and porous TiO2 coatings produced by micro-arc oxidation (MAO) were treated with NaOH etching or O2 plasma and then placed in contact with a reactive isocyanate test compound to evaluate the potential of molecule conjugation. Results suggested that O2 plasma treatment has only changed the surface chemistry of the coating through carbon contaminants removal, plasma-driven oxidation and generation of functional OH species, including reactive carboxyl groups. This chemical modification by plasma has made the surface superhydrophilic. After NaOH etching, the coating became rougher and also superhydrophilic, containing titanate structures doped with sodium and calcium on its surface and inside the inner pores. Upon reaction with butyl isocyanate, the O2 plasma-treated surfaces seem to better provide molecule conjugation, introducing characteristic conjugation bonds, and also making MAO coatings more hydrophobic due to the surface-terminated methyl chains from isocyanate. This proof-of-concept study has demonstrated the promising grafting potential given by O2 plasma on complex TiO2 surfaces.

Surface modification of WE43 Mg alloy via combination of cold spray and micro-arc oxidation for wear related applications at high temperatures

This study investigates the high temperature wear behaviour of a WE43 Mg alloy after covering it with single and dual layer coatings. For this purpose, cold spray and micro-arc oxidation processes were employed individually and sequentially. Single-layer coatings fabricated by cold spray and micro-arc oxidation processes were Al/Al2O3 composite and MgO-based ceramic, respectively. Sequential application of cold spray and micro arc oxidation processes induced dual layer coating upon synthesizing an external Al2O3–based layer over the Al/Al2O3 composite layer. Results of the wear tests conducted under the load of 2 N revealed the superior resistance of the dual layer coated sample against the rubbing action of the counterface compared to single layer coatings. Thus, the presence of a relatively hard and tough external Al2O3-based layer over the Al/Al2O3 composite layer sustained protection up to the temperature of 320 °C, where the dominant wear mechanism was fatigue wear. However, the increase in the test temperature to 350 °C caused detachment of the external Al2O3-based layer. Reduction of the wear test load from 2 to 1 N resulted in the remaining of external Al2O3-based layer intact with the underlying Al/Al2O3 composite layer even at a test temperature of 350 °C. It is therefore concluded that the combination of cold spray and micro-arc oxidation processes is promising to broaden the reliable use of WE43 and other Mg alloys in wear related applications at high service temperatures.

Surface Modification and Tribological Performance of Calcium Phosphate Coatings with TiO2 Nanoparticles on VT1-0 Titanium by Micro-Arc Oxidation

Surface Modification and Tribological Performance of Calcium Phosphate Coatings with TiO2 Nanoparticles on VT1-0 Titanium by Micro-Arc Oxidation

Organic-Inorganic Biocompatible Coatings for Temporary and Permanent Metal Implants

The general trend of increasing life expectancy will consistently drive the demand for orthopedic prostheses. In addition to the elderly, the younger population is also in urgent need of orthopedic devices, as bone fractures are a relatively common injury type; it is important to treat the patient quickly, painlessly, and eliminate further health complications. In the field of traumatology and orthopedics, metals and their alloys are currently the most commonly used materials. In this context, numerous scientists are engaged in the search for new implant materials and coatings. Among the various coating techniques, plasma electrolytic oxidation (PEO) (or micro-arc oxidation—MAO) occupy a distinct position. This method offers a cost-effective and environmentally friendly approach to modification of metal surfaces. PEO can effectively form porous, corrosion-resistant, and bioactive coatings on light alloys. The porous oxide surface structure welcomes organic molecules that can significantly enhance the corrosion resistance of the implant and improve the biological response of the body. The review considers the most crucial aspects of new combined PEO-organic coatings on metal implants, in terms of their potential for implantation, corrosion resistance, and biological activity in vitro and in vivo.

Investment casting of porous Mg-alloy networks biomechanically tuned for bone implant applications

Manufacturing technology has been refined and described for the fabrication of honeycomb-based bioresorbable networks for temporal bone replacement applications. Two novel techniques, digital light processing and investment casting, were utilized to produce customized, shape-optimized cellular constructs with additional orifices promoting tissue ingrowth during osteo-regeneration. For this purpose, a conventional magnesium casting alloy (AZ91) was chosen. Numerical simulations were conducted to predict the compressive behavior of the proposed biodegradable lightweight scaffolds. Spatial castings were adjusted to possess mechanical properties comparable to the ones of cortical or trabecular bones. Two kinds of protective coatings (plasma electrolytic oxidation and organic ones based on natural polyphenols from tea extract) were deposited and characterized. They can be utilized to control the degradation rate during exploitation to achieve a predictable implant lifespan. The elaborated layers aim to mitigate the rapid corrosion of magnesium substrates by prolonging their bioresorption time and thus expanding their applicability in osseointegration. To evaluate this assumption, immersion tests in phosphate-buffered saline were performed, showing better chemical resistance of PEO coating and as-cast sample (for both mass gain by below 1%), and visible increase in mass of sample coated with organic coating (increase by almost 5%). Compressive strength results from numerical approach were further validated by experimental compression tests, showing that PEO coating deteriorated compressive strength by almost 3%, and organic coating improved it by over 9%. Results achieved in numerical approach were better than expected for stiffer sample, and slightly lower for the one with bigger pores.

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.