Micro-arc Oxidation Ceramic Coatings Research Articles

Effects of nano-SiO2 particle addition on the structure and properties of micro-arc oxidation ceramic coatings on 7075 aluminum alloy

Purpose The purpose of this study is to investigate the influence of varying concentrations of nano-SiO2 particle doping on the structure and properties of the micro-arc oxidation (MAO) coating of 7075 aluminum alloy. This research aims to provide novel insights and methodologies for the surface treatment and protection of 7075 aluminum alloy. Design/methodology/approach The surface morphology of the MAO coating was characterized using scanning electron microscope. Energy spectrometer was used to characterize the elemental content and distribution on the surface and cross section of the MAO coating. The phase composition of the MAO coating was characterized using X-ray diffractometer. The corrosion resistance of the MAO coating was characterized using an electrochemical workstation. Findings The results showed that when the addition of nano-SiO2 particles is 3 g/L, the corrosion resistance is optimal. Originality/value This study investigated the influence of different concentrations of nano-SiO2 particles on the structure and properties of the MAO coating of 7075 aluminum alloy.

Tribological properties of MAO ceramic coatings with annulus array texture on disposable surgical gloves.

Introduction: In recent research, the expansion in the use of Mg alloys for biomedical applications has been approached by modifying their surfaces in conjunction with micro-arc oxidation (MAO) techniques which enhance their abrasion and corrosion resistance. Methods: In this study, combining laser texturing and MAO techniques to produce the dense ceramic coatings with microstructures. On the surface of the AZ31 Mg alloy, a micro-raised annulus array texture has been designed in order to increase the surface friction under liquid lubrication and to improve the operator's grip when holding the tool. For this work, the micro-morphology of the coatings was characterised, and the friction properties of the commonly used scalpel shank material 316L, the untextured surface and the textured surface were comparatively analysed against disposable surgical gloves. Results and discussion: The results show that the Laser-MAO ceramic coating grows homogenous, the porosity decreases from 14.3% to 7.8%, and the morphology after friction indicates that the coating has good wear resistance. More specifically, the average coefficient of friction (COF) of the three types of gloves coated with Laser-MAO ceramic was higher than that of the 316L and MAO ceramic coatings under the action of the annulus-integrated texture under the lubrication conditions of physiological saline and defatted sheep blood, which achieved the goal of increasing friction for the purpose of helping to prevent the problem of tool slippage from the hand.

Preparation and properties of micro-arc oxidation ceramic coatings using machine vision technology

In this paper, a machine vision system is combined with non-immersion micro-arc oxidation (MAO) technology, using color as a visual feature, and automatically determining the MAO process through a self-developed color image segmentation program for HSV channel. The robotic arm accurately regulates the machining position and duration. Dense ceramic oxide coatings of similar quality to the artificially prepared coatings were successfully prepared on aluminum (Al) surface. The surface morphology and elemental composition of the samples were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The performance of the coatings was tested through thickness tests, hardness tests, and roughness tests. The tribological properties were tested by friction experiments, and its corrosion resistance was tested by electrochemical corrosion tests. The results confirm the effectiveness of a machine vision system for MAO process control, which is capable of preparing high-quality coatings comparable to manual operations. This not only solves the need for precise film formation in different application scenarios, but also provides a more efficient, controllable and innovative solution for the MAO process.

Stress corrosion crack propagation behaviour of MAO ceramic coating on Mg alloy

This study investigates the impact of static tensile loads on magnesium (Mg) alloys with and without ceramic coatings in simulated body fluids (SBF) using a combination of numerical simulation and experimental methods. The surface of an AZ31B Mg alloy was treated with a ceramic coating via micro-arc oxidation (MAO). Subsequently, bare Mg-alloy and MAO ceramic-coated specimens were subjected to static tensile stress testing using a tensiometer. After immersion for 12 h in SBF, the surface morphology and electrochemical corrosion of the stressed specimens were analysed. Notably, under the same tensile stress, the Mg alloy in the SBF exhibited more severe corrosion damage than the ceramic-coated specimen. Furthermore, there was a direct correlation between the corrosion rate of the ceramic coating and the magnitude of the applied tensile stress. Overall, the MAO ceramic coating exhibited superior corrosion resistance compared to the bare Mg alloy, even after undergoing static tensile stresses. The study demonstrates that MAO ceramic coatings can enhance the corrosion resistance of biodegradable Mg implants by protecting them from the combined effects of bodily stresses and fluids.

In situ formation of micro arc oxidation ceramic coating on refractory high entropy alloy

Micro arc oxidation (MAO) coatings were in situ prefabricated on refractory high entropy alloys (RHEAs). We systematically studied the evolution of the surface and cross-sectional morphologies and composition of the MAO ceramic coatings on AlTiCrVZr substrate with oxidation time. It was found that the surface elements in AlTiCrVZr exhibit competitive oxidation behavior during the MAO process. The inner layer of the MAO ceramic coating was mainly composed of ceramic oxides of the substrate elements, and the outer layer primarily consisted of ceramic oxides formed by the solute ions. Finally, we propose a growth model of the ceramic oxide coatings based on the formation mechanism of the MAO ceramic coating and the physical and chemical properties of the ceramic oxides formed by the principal elements in the RHEAs.

Effects of voltage on microstructure and properties of micro-arc oxidation ceramic coatings on AZ31B magnesium alloy under constant current–constant voltage operation mode

Purpose The purpose of this paper is to study the effects of voltage on microstructure and properties of micro-arc oxidation (MAO) ceramic coatings formed on AZ31B magnesium alloy under the constant current–constant voltage operation mode. Design/methodology/approach The wear and corrosion resistance of MAO coating on AZ31B magnesium alloy was studied by MAO in silicate electrolyte under constant current and constant voltage. Findings When the voltage is 360 V, the wear and corrosion resistance of AZ31B magnesium alloy is the best. Originality/value The wear and corrosion resistance of MAO coating on AZ31B magnesium alloy was studied by friction wear and electrochemical workstation.

Effect of ultra accurate control of electrolyte temperature on the performance of micro arc oxidation ceramic coatings

The technique of micro arc oxidation (MAO) uses arc discharge and high-voltage breakdown to produce a ceramic layer on valve metal surfaces. However, the common method of MAO requires immersing the workpiece in an electrolyte solution, which can result in elevated temperatures due to the arc discharge, thus negatively affecting the coating's quality and performance. This article investigates the influence of electrolyte temperature on the performance of MAO ceramic coatings, with the assistance of a robotic arm enabling valve metal reaction without immersion in the electrolyte, and precise control of electrolyte temperature through a MAO temperature monitoring system. Various techniques, such as scanning electron microscopy (SEM), hardness testing, electrochemical corrosion experiments, and friction-wear experiments, were utilized to characterize the performance of the prepared coating. The results indicate a nonlinear correlation between the temperature of the electrolyte and the thickness and hardness of the ceramic coating. The corrosion and wear resistance of the MAO ceramic coatings initially improve with increasing electrolyte temperature but eventually deteriorate. At an electrolyte temperature of 40 °C, the MAO ceramic coating exhibits the optimal corrosion and wear resistance. The variation in electrolyte temperature affects the reactivity of the electrolyte ions, leading to changes in the morphology and properties of the resulting MAO ceramic coating. These findings offer valuable insights into the interaction mechanism between electrolyte temperature and the properties of the resulting MAO ceramic coating. This is of great significance in optimizing the MAO process for specific applications and improving the overall performance of ceramic coatings.

Synergistic effect of “double pores” texture on tribological properties of AZ31 Mg alloy micro-arc oxide ceramic coatings

Micro-arc oxidation (MAO) technology for the generation of ceramic coatings on metal surfaces have been gradually used for protecting metal components from the severe wear and corrosion attack. In this study, laser texturing was applied to ameliorate the MAO ceramic coating. The scalability of ceramic coated samples by laser texturing technology was scrutinized in terms of microstructure, coefficient of friction (COF) and corrosion resistance. It turns out that the “Double pores” system generated by laser structuring of the substrate before MAO treatment has the capacity to enhance the tribological properties of the ceramic coating. After laser structuring, the proportion of magnesium oxide in the ceramic coating generated by the Mg alloy substrate increases, which is due to the oxidation of the magnesium substrate by the high temperature laser. At the same time, it also accounts for the increase in cracks on the surface of the coating. In addition, the presence of cracks has an impact on the corrosion resistance of the ceramic coating. Interestingly, the COF of the treated ceramic coating becomes lower and the heat from the texturing process has a “Quenching effect” on the substrate. In general, the COF of the ceramic coating on the surface of the laser texturing Mg substrate is reduced by 31 % compared to the original ceramic coating, at the expense of some corrosion resistance.

Study on Growth Mechanism and Characteristics of Zirconium Alloy Micro-Arc Oxidation Film

Ceramic coatings on R60705 zirconium alloy were prepared on the surface by the micro-arc oxidation (MAO) technique in electrolytes containing Na2SiO3, NaOH, and Na2EDTA. The growth behavior of the MAO ceramic coatings at different stages, including growth rate, microstructure, and phase composition, was investigated using the method of direct observation of the boundary area. The results showed that the growth of the MAO coatings on R60705 zirconium alloy occurred in both inward and outward directions. At an oxidation time of 5 min, the thickness of the oxidation layer increased fastest, reaching 103.43 μm, with a growth rate of 0.345 μm/s. After 5 min, the growth rate decreased and tended to level off around 15 min, with a thickness and growth rate of 162.7 μm and 0.181 μm/s, respectively. The total thickness of the coatings continuously increased throughout the process, with the outward growth thickness always higher than the inward growth thickness. The composition of the zirconium alloy micro-arc oxidation coatings mainly consisted of monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2), and a small amount of SiO2. The main elements in the coatings were Zr, O, and Si. The corrosion resistance of the zirconium alloy micro-arc oxidation coatings increased first and then decreased with increasing oxidation time, with a corrosion current density of 8.876 × 10−9 A·cm−2 at 15 min, indicating the best corrosion resistance.

Effect of Pre-Anodized Film on Micro-Arc Oxidation Process of 6063 Aluminum Alloy.

In the current investigation, micro-arc oxidation (MAO) ceramic coatings on aluminum are galvanostatically synthesized at various processing stages in an alkaline silicate system. The resultant coatings are systematically investigated in terms of the following respects: The working voltage and surface sparking evolution over the studied course of MAO are recorded by the signal acquisition system and the real-time imaging, respectively; the phase composition, the surface morphology, and the polished cross-section of the coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with an energy-dispersive X-ray spectrometer (EDS), respectively. In particular, with the help of a low-rate increase in working voltage, the evolution of the sparks, the energy consumption, and the microstructure development of aluminum in alkaline silicate electrolyte by pre-anodizing are systematically investigated. The results show that the pre-anodized film can accelerate the evolution process of MAO spark and shorten the reaction process in the early stage of MAO reaction, reducing energy consumption and improving the corrosion resistance of the MAO coating. The γ-Al2O3 phase content after pre-anodized is significantly increased in MAO coatings. In particular, the thicker the pre-anodized film (beyond 8 μm) was broken down and fragmentation thinning in the early stage of the MAO process with the presence of micro discharges. This is due to the fact that the electron transition will be released by the emission of radiative recombination and reveals obvious galvanoluminescence (GL) behavior on the surface of the pre-anodized film. Further, based on the present MAO coating microstructure, a model of coating growth after pre-anodized that evolves over time is proposed.

Effect of nickel-coated carbon nanotubes on the preparation and wear resistance of microarc oxidation ceramic coating on ZL109 aluminum alloy

In order to adapt to the development of lightweight equipment, and further improve the wear resistance of ZL109 aluminum alloy, the influence of nickel-coated carbon nanotubes as an electrolyte additive on the preparation and wear resistance of microarc oxidation ceramic coatings on ZL109 aluminum alloy surface was investigated. In this work, 0.4 g/L, 0.8 g/L, 1.2 g/L, 1.6 g/L, and 2 g/L nickel-coated carbon nanotubes were added to the electrolyte respectively. The microarc oxidation ceramic coatings were prepared under bipolar pulse constant pressure mode, which were analyzed from the aspects of morphology, chemical composition, and wear resistance property. The results show that the nickel-coated carbon nanotubes possess a great influence on ceramic coatings. The morphology of ceramic coatings was significantly changed. In this work, the coating prepared by 1.2 g/L nickel-coated carbon nanotubes exhibits excellent wear resistance property.

Microstructure and Properties in Simulated Seawater of Copper-Doped Micro-arc Coatings on TC4 Alloy

Micro-arc oxidation (MAO) ceramic coatings were prepared on TC4 titanium alloys by adding CuSO4 to a (NaPO3)6 base solution. The microstructures of the MAO coatings were characterized by scanning electron microscopy (SEM), energy dispersive (EDS), and X-ray photoelectron spectroscopy (XPS). The corrosion resistance and wear resistance of these coatings were evaluated via hydrochloric acid immersion of weight deficit and friction tests. Those results indicated the presence of Cu in the MAO coating in the form of CuO and Cu2O. Incorporation of CuSO4 results in a thickness and roughness increase in the coating. The coating has a lower coefficient of friction (0.2) upon the addition of 4 g/L of CuSO4. The antibacterial properties of the MAO coatings were maximized at 6 g/L of CuSO4. However, the corrosion resistance of the copper-doped MAO coating did not exceed the undoped coating. This study shows that the addition of CuSO4 to the electrolyte successfully prepared copper-containing micro-arc oxidation coatings, which improved the wear resistance and antibacterial properties of the coating.

Effect of carbon nanotubes additive on tribocorrosion performance of micro-arc oxidized coatings on Ti6Al4V alloy

Ti6Al4V alloy subjected to the combined effects of wear and corrosion (tribocorrosion) in corrosive media shows severe deterioration. This study aimed to investigate the tribocorrosion behavior of oxide films produced by micro-arc oxidation (MAO) in a 3.5% NaCl solution. MAO ceramic coatings were obtained on Ti6Al4V alloy using the MAO process in alkaline electrolytes with different carbon nanotubes (CNTs) concentrations. The morphology and composition of MAO coatings were investigated using SEM, XRD, and Raman spectroscopy. Their friction reduction and wear resistance performance was evaluated under dry sliding conditions. Potentiodynamic polarization was used to assess the corrosion resistance of the MAO-coated Ti6Al4V specimens. Tribocorrosion behavior was evaluated by the evolution of open circuit potential (OCP) and coefficient of friction (COF) before, during, and after reciprocating sliding. The results showed that CNTs were incorporated in MAO coatings obtained in electrolytes containing CNTs and enhanced MAO coatings' corrosion and tribocorrosion resistance. The MAO coatings obtained in electrolytes containing 0.15 g/L CNTs possessed the best corrosion and tribocorrosion resistance.

Growth characteristics and properties of micro-arc oxidation coatings on AlSi10Mg selective laser-melted components

Micro-arc oxidation (MAO) ceramic coatings were prepared on porous AlSi10Mg selective laser-melted components to improve their corrosion property. The microstructure and composition of the coatings at different processing times were characterized via scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. Results showed that the diameter of micro-pores increased with an extension of treatment time, the porosity of coatings decreased from 6.24% to 0.85%. Thickness increased from 4.45 ± 0.01 μm to 15.20 ± 0.01 μm and surface roughness increased from 0.76 ± 0.01 μm to 5.41 ± 0.01 μm with increasing processing time. Meanwhile, the coatings were mostly composed of γ-Al2O3 and trace amounts of α-Al2O3, Al2SiO5, AlPO4 and WO3, the content of α-Al2O3 was increased from 0.51% to 4.12%. Corrosion current density decreased from 2.213 e−5 A·cm−2 to 1.088 e−7 A·cm−2. The polarization resistances Rb were increased from 4.8 × 103 Ω·cm2 to 2.6 × 105 Ω·cm2. The long term EIS results show that Rb was 7.7 × 103 Ω·cm2 after 3 weeks immersion, which show that the MAO coatings could provide good protection on AlSi10Mg alloy. The gas holes and defects of the SLM components were treated via MAO to form uniform MAO coatings on the surface of a sample, expanding the application range of selective laser-melted components in corrosive environments.

In Situ Preparation of Mg-Al-Co Layered Double Hydroxides on Microarc Oxidation Ceramic Coating of LA103Z Magnesium-Lithium Alloy for Enhanced Corrosion Resistance

In Situ Preparation of Mg-Al-Co Layered Double Hydroxides on Microarc Oxidation Ceramic Coating of LA103Z Magnesium-Lithium Alloy for Enhanced Corrosion Resistance

Tribological properties of MAO/MoS2 self-lubricating composite coating by microarc oxidation and hydrothermal reaction

To decrease coefficient of friction (CoF) of the 6063 aluminum alloy modified by microarc oxidation (MAO) treatment, a MoS2 lubricating layer was synthesized on the MAO coating by hydrothermal reaction. The as-synthetized MoS2 powders demonstrated high purity and interesting micro-spheres structure assembled by many nano-lamellae. The prepared MoS2 layer was ~11 ± 3.3 μm thick, and padded the surface porosity of MAO ceramic coatings. These composite coatings were slidden against GCr15 steel counterparts in air at variable applied loads. According to the results of tribological test, the CoF of MAO/MoS2 composite coatings reduced by ~31.4%, 45.5% and 42.1% compared to single MAO coatings at 2, 4 and 6 N loads, respectively, due to the low shear strength of MoS2. The wear track of MAO/MoS2 composite coatings also displayed more uniform and smoother, causing more stable sliding process. Additionally, the existence of MoS2 layer significantly decreased the wear rate of both coatings and related counterpart balls, implying the enhanced anti-wear properties. Scanning electron microscopy (SEM) and Raman spectrometer revealed that the primary wear mechanism of single MAO coating was a combination of adhesive wear, abrasive wear and oxidation, while the MAO/MoS2 self-lubricating composite coating only showed slight abrasive wear combined with oxidation occurrence.

Microstructure and wear resistance of micro-arc oxidation ceramic coatings prepared on 2A50 aluminum alloys

With a bipolar pulse power, wear-resistant ceramic coatings with high micro-hardness were in-situ fabricated on 2A50 aluminum alloy using micro-arc oxidation method in silicate electrolyte. The effect of cathodic voltage on microstructure, phase structure, micro-hardness and wear properties was investigated by changing cathodic voltage from 0 to −200 V. The phase structure, microstructure, micro-hardness and wear resistance were determined by XRD, SEM, HVS-1000 Vicker's micro-hardness tester and tribology tester. The results show that the phase of the obtained coatings is mainly composed of γ-Al2O3. The coating consists of the inner dense layer and the outer loose layer. As the cathodic voltage increases, the quantity and size of the micro-pores in the coatings first decrease and then increase. Micro-arc oxidation can greatly strengthen 2A50 aluminum alloy, the micro-hardness increases from 75 HV0.5 to 1321 HV0.5 after a micro-arc oxidation under a cathodic voltage of −100 V. The friction coefficient of the ceramic coatings are in the range of 0.35–0.55, and the coating obtained under −100 V exhibits the best wear resistance. The wear mechanism is deduced to be the combination of abrasive and adhesive wear.

Preparation and performance of alumina ceramic coating doped with aluminum nitride by micro arc oxidation

The present work is focused on the preparation and performance of micro arc oxidation (MAO) ceramic coating doped with aluminium nitride (AlN) on 6061 Al alloy. The results reveal that AlN-doped ceramic coatings could be prepared by plasma discharge with AlN powder or urea added into the electrolyte. Although AlN-doped MAO ceramic coatings present more distinct porous features than those without AlN, they achieved excellent thermal conductivity and insulation performance due to the physical properties of AlN. Compared with the uncoated Al substrate, MAO coatings with or without AlN doping all exhibited an improved wear resistance. AlN-doped MAO coating could considerably inhibit the formation of a transfer layer. This alumina ceramic coating doped with AlN is anticipated to be applied in the field of light-emitting diode (LED) aluminum substrate.

Synthesis, corrosion, and wear resistance of a black microarc oxidation coating on pure titanium

Black microarc oxidation (MAO) ceramic coatings were prepared on TA2 pure titanium by adding the colorant [Cu(NH3)4]2+ to a Na2SiO3 base solution. The microstructures of the MAO coatings were characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. The corrosion resistance and wear resistance of the coatings were evaluated through potentiodynamic polarization and friction tests. [Cu(NH3)4]2+ was absorbed into the pores of the microarc discharge to form black copper oxide under high temperature and pressure. Cu content in the MAO coating increased with [Cu(NH3)4]2+ concentration. The wear resistance and hardness of the prepared black ceramic coatings were remarkably improved in terms of self-sealing microstructure. However, the corrosion resistance of the black coatings was approximately one or two orders of magnitude lower than that of the MAO coating without Cu doping. This study shows that the proposed method is a promising method for preparing decorative coating or absorbing light coating on a titanium surface.

Study on Preparation, Microstructure and Properties of Micro-Arc Oxidation Ceramic Coating on AZ91 Magnesium Alloy in Phosphate Electrolyte

The micro-arc oxidation behavior of AZ91 magnesium alloy in alkaline phosphate electrolyte was studied. The effect of phosphate on the microstructure and properties of micro-arc oxide film was investigated and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectrum (EDS) and salt spray test. The results show that phosphate concentration has an important effect on the surface morphology, phase structure, thickness and corrosion resistance of micro-arc oxidation film. With the increase of phosphate concentration from 5g/L to 30g/L, the film quality decreases, the surface roughness increases, the thickness decreases and the corrosion resistance decreases. So in phosphate electrolysis the lower phosphate concentration in the liquid system is helpful to the formation of better film quality.