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The paper presents the results of microarc oxidation of porous aluminum made of alloys AlSi15, Д16 (D16) and AlMg6. According to research, on the surface of the sample, a composite oxide-ceramic coating is formed, consisting of mullite 3Al2O3‧2SiO2 and (or) various forms of aluminum oxide (α-, γ-Al2O3). It is shown that on the surface of porous aluminum, as well as in the pores of a cast sample, a coating is formed consisting of electropositive and electronegative sorption materials, aluminum oxides and aluminosilicates. Moreover, by changing the composition of the aluminum alloy and micro-arc oxidation modes, it is possible to control the phase composition of the coating being formed, which opens up the possibility of creating selective filter devices to retain either anionic or cationic inorganic compounds and microbiological objects.

This article is dedicated to investigating the impact of different electrolyte compositions on the development of titanium coatings endowed with superior mechanical, tribological, and corrosion properties. An experimental analysis was conducted on three distinct electrolyte formulations, each contributing unique attributes to the coating's structural formation. Advanced analytical techniques, including scanning electron microscopy, hardness testing, wear resistance evaluation, and corrosion trials in harsh environments, were employed to gauge the mechanical, tribological, and anti-corrosive performance of the coatings. The utilization of scanning electron microscopy, X-ray structural analysis, and additional methodologies enabled an in-depth characterization of the microstructure and elucidated the relationship between the physico-mechanical properties and the electrolyte's chemical makeup. Among the electrolytes examined, the composition containing potassium hydroxide emerged as superior, fostering coatings with a distinctively porous structure that augment mechanical attributes. A considerable degree of porosity coupled with relatively small pore dimensions suggests the potential to engineer structures that exhibit optimal mechanical robustness. Furthermore, research findings related to this specific electrolyte composition revealed enhancements in the friction coefficient and wear resistance, indicating its promising prospects for tribological applications. The study also meticulously addressed the corrosion aspects, revealing that the microarc oxidation-derived coatings substantially improve corrosion resistance by offering more favorable potentials and currents than the bare titanium substrate. The efficacy of microarc oxidation as an avant-garde technique to advance the properties of titanium alloys underscores its prospective utility and practical relevance in contemporary industrial applications.

The correlation between negative pulse and the black electrolyte properties of magnesium alloy micro-arc oxidation and the treated area was investigated by introducing a negative pulse electric field. The physical phase composition, microstructure, elemental distribution, and content of the coating were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results showed that the introduction of negative pulses favored the generation of MgO and MgSiO3 contents in the coatings, and an increase in the MgO phase was found in the coatings formed in the failed electrolytes; the microporous size and microcracks of the coatings were gradually and significantly reduced; the average consumption of Cu ions was 0.0453 g/L·dm2, which is only 26% of that in the unipolar condition; the introduction of the negative pulses significantly improved the "anomalous consumption" of Cu ions. The introduction of negative pulse can significantly improve the "abnormal consumption" of copper ions, which is attributed to the change in the electric field by negative pulse, which makes the cathode-enriched Cu ions migrate to the anode and reduces the reduction and precipitation of Cu ions at the cathode. [ABSTRACT FROM AUTHOR]

The work addresses the issues of controllability of the microarc-oxidation process. This problem is mostly due to the difficulty of analytically characterizing the heterogeneous physical–chemical processes, which are nonlinear and nonstationary, that take place during microarc oxidation. To tackle this issue, a digital twin of the process is being developed, within which an analytical model is proposed to describe the behavior of the equivalent electrical circuit of the galvanic cell during coating deposition. The proposed analytical model of the process is nonlinear and nonstationary, which is attributed to the abrupt decrease in the active resistance of the coating during dielectric breakdowns. Based on experimentally obtained current and voltage oscillograms and the proposed analytical model, parametric identification of the electrical parameters of oxide coatings is performed using the matrix-operator method on the orthonormal Walsh basis. The matrix-operator method is selected because of its applicability to solving problems with both linear and nonlinear equations, as well as stationary and nonstationary parameters and variables, along with the relative simplicity of the mathematical and algorithmic implementation of computations. The calculations result in weight functions of the electrical model of the microarc-oxidation process, reflecting the relationship between the voltage and current in the galvanic cell (coating conductivity). The mean values of the weight functions (average conductivity) decrease during coating deposition, which confirms the adequacy of the proposed model and enables its use for implementing real-time procedures for monitoring coating properties. The scientific novelty of the work lies in the possibility of the real-time control of microarc oxidation through parametric identification of the electrical parameters of coatings using the matrix-operator method. [ABSTRACT FROM AUTHOR]

This article is dedicated to investigating the impact of different electrolyte compositions on the development of titanium coatings endowed with superior mechanical, tribological, and corrosion properties. An experimental analysis was conducted on three distinct electrolyte formulations, each contributing unique attributes to the coating's structural formation. Advanced analytical techniques, including scanning electron microscopy, hardness testing, wear resistance evaluation, and corrosion trials in harsh environments, were employed to gauge the mechanical, tribological, and anti-corrosive performance of the coatings. The utilization of scanning electron microscopy, X-ray structural analysis, and additional methodologies enabled an in-depth characterization of the microstructure and elucidated the relationship between the physico-mechanical properties and the electrolyte's chemical makeup. Among the electrolytes examined, the composition containing potassium hydroxide emerged as superior, fostering coatings with a distinctively porous structure that augment mechanical attributes. A considerable degree of porosity coupled with relatively small pore dimensions suggests the potential to engineer structures that exhibit optimal mechanical robustness. Furthermore, research findings related to this specific electrolyte composition revealed enhancements in the friction coefficient and wear resistance, indicating its promising prospects for tribological applications. The study also meticulously addressed the corrosion aspects, revealing that the microarc oxidation-derived coatings substantially improve corrosion resistance by offering more favorable potentials and currents than the bare titanium substrate. The efficacy of microarc oxidation as an avant-garde technique to advance the properties of titanium alloys underscores its prospective utility and practical relevance in contemporary industrial applications. [ABSTRACT FROM AUTHOR]

This work proposed a strategy of indirectly inducing uniform microarc discharge by controlling the content and distribution of β-Mg17Al12 phase in AZ91D Mg alloy. Two kinds of nano-particles (ZrO2 and TiO2) were designed to be added into the substrate of Mg alloy by friction stir processing (FSP). Then, Mg alloy sample designed with different precipitated morphology of β-Mg17Al12 phase was treated by microarc oxidation (MAO) in Na3PO4/Na2SiO3 electrolyte. The characteristics and performance of the MAO coating was analyzed using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact angle meter, and potentiodynamic polarization. It was found that the coarse α-Mg grains in extruded AZ91D Mg alloy were refined by FSP, and the β-Mg17Al12 phase with reticular structure was broken and dispersed. The nano-ZrO2 particles were pinned at the grain boundary by FSP, which refined the α-Mg grain and promoted the precipitation of β-Mg17Al12 phase in grains. It effectively inhibited the "cascade" phenomenon of microarcs, which induced the uniform distribution of discharge pores. The MAO coating on Zr-FSP sample had good wettability and corrosion resistance. However, TiO2 particles were hardly detected in the coating on Ti-FSP sample. [ABSTRACT FROM AUTHOR]

The repair and reconstruction of large bone defects after bone tumor resection is still a great clinical challenge. At present, orthopedic implant reconstruction is the mainstream treatment for repairing bone defects. However, according to clinical feedback, local tumor recurrence and nonunion of bone graft are common reasons leading to the failure of bone defect repair and reconstruction after bone tumor resection, which seriously threaten the physical and mental health of patients. On this basis, here the self-developed low modulus Ti-12Mo-10Zr alloy (TMZ) was chosen as substrate material. To improve its biological activity and osteointegration, calcium, oxygen, and phosphorus co-doped microporous coating was prepared on TMZ alloy by microarc oxidation (MAO). Then, black phosphorus (BP) nanosheets were incorporated onto MAO treated TMZ alloy to obtain multifunctional composites. The obtained BP-MAO-TMZ implant exhibited excellent photothermal effects and effective ablation of osteosarcoma cancer cells under the irradiation of 808 nm near infrared laser, while no photothermal or therapeutic effects were observed for TMZ alloy. Meanwhile, the structure/component bionic coating obtained after MAO treatment as well as the P-driven in situ biomineralization performance after incorporation of BP nanosheets endowed BP-MAO-TMZ implant with synergistic promoting effect on MC3T3-E1 osteoblasts' activity, proliferation and differentiation ability. This study is expected to provide effective clinical solutions for problems of difficult bone regeneration and tumor recurrence after tumor resection in patients with bone tumors and to solve a series of medical problems such as poor prognosis and poor postoperative quality of patients life with malignant bone tumors. [ABSTRACT FROM AUTHOR]

Microarc oxidation is a promising technology for producing wear-resistant anticorrosive coatings for goods made of valve metals and alloys and is used in many industries. One of the main problems of this technology is low controllability caused by the complexity and interconnectedness of physical and chemical phenomena occurring during the coating process. To solve such problems, digital twins are currently actively used. The paper covers the development of mathematical models that are advisable to use as structural elements of the digital twin of the microarc oxidation process. An equivalent electrical circuit of a galvanic cell of microarc oxidation is given, which takes into account the electrolyte resistance, the part coating resistance in the form of a parallel connection of nonlinear active resistance and capacitive reactance. The authors propose a mathematical model describing the behavior of the equivalent electrical circuit of a galvanic cell of microarc oxidation. A technique for determining the parameters of this model was developed, including the construction of a waveform of changes in the resistance of the cell and its approximation, estimation of the values of resistances and capacitance of the galvanic cell equivalent circuit. The authors proposed a calculation method and developed a Simulink model of the microarc oxidation process, which allows simulating the current and voltage waveforms of a galvanic cell. The analysis of the model showed that the model is stable, controllable and observable, but poorly conditioned, which leads to modelling errors, the maximum value of which is 7 % for voltage and 10 % for current. By the parametric identification method using experimental current and voltage waveforms, the dependences of the parameters of the galvanic cell equivalent circuit on the oxidation time are obtained. It is found that the change in the period average of the galvanic cell active resistance correlates with the coating thickness.

MgO@Nb2O5 composite coating was prepared on the surface of Mg–7Y alloy by micro-arc oxidation technique. The microstructure of the composite coatings was tested by scanning electron microscopy, energy spectrum analysis, X-ray diffraction and scanning kelvin probe force microscope. The hydrothermal performance and corrosion resistance of MgO@Nb2O5 composite coatings were analyzed by electrochemistry tests and laser confocal. The results showed that microspore diameter, porosity and roughness of the composite coatings were all decreased with the increasing of Nb2O5 concentration. The micro-arc oxidation composite coatings were mainly composed of MgO and Nb2O5. Compared with the micro-arc oxidation coating without Nb2O5, the corrosion voltage of the micro-arc oxidation coating with Nb2O5 was increased and the corrosion current was reduced. The corrosion resistance of Mg–7Y alloy was effectively improved by the MgO@Nb2O5 composite coatings, and the best corrosion resistance of the micro-arc oxidation coating was achieved when the Nb2O5 concentration was 2 g/L. The hydrothermal test demonstrated that the hydrothermal resistance of the coatings was significantly improved due to the addition of Nb2O5.

For the first time, a promising method for protecting the surface of metals and alloys from external high-temperature effects is proposed and substantiated experimentally by creating a functionally graded coating with a finishing ceramic layer and a precursor intermetallic layer. The technology of gas dynamic cold spraying of a mechanical mixture of powders based on aluminum valve metal with heat treatment is developed. [ABSTRACT FROM AUTHOR]

It is known that the methods of electrolytic oxidation, including traditional anodizing and microarc oxidation, implemented according to classical schemes in electrolytic baths with mechanical, pneumatic, and magnetic mixers, cannot provide high-quality homogeneous oxide coatings on the inner surfaces of products made from valve metal alloys. In this paper, the principal possibility of obtaining high-quality uniform coatings on the extended internal surfaces of products, including the surfaces of deep holes, when an electrolyte solution is passed through them, is revealed. It has been experimentally proved that, based on the proposed approach, it is possible to process products with deep holes, achieving a ratio of both minimum and maximum values of the thickness and the breakdown voltage of coatings on the internal and external surfaces in a range of 0.85–0.93. A possibility of forming coatings exclusively on the internal surfaces of products without changing the state of their external surfaces, moreover, without using expensive electrolytic baths—inside internal cavities of products themselves, is shown. A good correlation between the values of the thickness and of the breakdown voltage of coatings has been established. As a result, a possibility of indirectly determine the coatings thickness based on the results of their breakdown voltage measuring has been substantiated. [ABSTRACT FROM AUTHOR]

The influence of the parameters of thermal, electrochemical, and microarc oxidation on the laws of formation of oxide barrier coatings on a VT23 titanium alloy (Ti–Al–V–Mo–Cr–Fe system) is studied. The resistance of the formed coatings to the subsequent vacuum annealing at 800°C for 1 h is examined. The coating thickness is shown to increase with the oxidation temperature or voltage. The coatings produced by thermal and microarc oxidation are most resistant to heating in vacuum, but those produced by microarc oxidation contain pores. The anodic oxide coating is completely dissolved upon vacuum annealing. [ABSTRACT FROM AUTHOR]

A MA8 magnesium alloy substrate was pre-impregnated in aqueous solutions of cerium(III) nitrate and glycerol before microarc oxidation, which was used to form oxide ceramic coatings from a silicate–alkaline electrolyte containing fluoride ions. The corrosion-protection properties of these coatings on the pre-impregnated alloy surface were assessed using potentiodynamic polarization curves. Electrochemical parameters calculated from the potentiodynamic polarization curves showed that the presence of the oxide ceramic coating on the surface of MA8 magnesium alloy significantly reduces the corrosion current density and increases the polarization resistance. It was determined that the pre-impregnation of the MA8 magnesium alloy substrate in aqueous solutions of cerium(III) nitrate and glycerol affects the mechanism of the corrosion damage. [ABSTRACT FROM AUTHOR]

Poor corrosion resistance of magnesium alloys dramatically limits their application in corrosive environments.Microarc oxidation(MAO) technology can prepare a ceramic-like coating on the surface of magnesium alloy，which is an effective method to improve its corrosion resistance.Due to the film formation mechanism of MAO technology，there are many pores and cracks in the coating，and usually the coating is mainly composed of MgO，which would absorb water or deliquesce in wet and acidic environments，making the coating present bad corrosion resistance.Incorporating ZrO2 with excellent chemical stability and high hardness into magnesium alloy MAO coating to obtain a coating mainly composed of ZrO2 or a ZrO2-containing coating can improve the protection effect on the substrate.This paper reviewed the research progresses of the preparation technology，film formation mechanism and corrosion resistance of ZrO2-containing MAO composite coatings on magnesium alloys from the aspects of electrolyte，electric parameter，two-step MAO process，and combining MAO with other surface treatment techniques.In addition，the problems and shortcomings of each research direction were analyzed.In the future，it is necessary to optimize the electrolyte composition to ensure its stability and effectiveness and clarify the consumption and replenishment rules of each electrolyte component during the usage.The two-step MAO process should be further studied to obtain a composite MAO coating with better protection effect on the magnesium alloy matrix.Combination of MAO and other surface treatment techniques should be explored to utilize the advantages of two technologies and coatings comprehensively.The temperature field distribution and MAO coating forming mechanism can be further analyzed based on the structure transformation of ZrO2 at different temperatures.

Questions of raising the efficiency and controllability of the process of depositing protective microarc oxide coatings with specified properties on products made of light metals and alloys (aluminum, magnesium, titanium) are examined. An intelligent information-measurement system is developed for measuring the parameters of microarc oxide coatings which contains unique hardware, program, and information support. For the hardware support of the system a technological current source is created that specifies the technical regimes, strength and shape of the current (a sinusoidal or pulsed signal is possible) which to a great extent determines the parameters of the formed coatings. Original circuit solutions in the area of pulsed power electronics, along with modern electronic components, are used for developing the source. The technological current source has a high efficiency and provides a complete range of regulation of the parameters of the energy effect on a test sample where a coating is being formed. The developed intelligent informationmeasurement system is intended for high current measurements of the process parameters and properties of the resulting coatings; it can be used for automatic monitoring of microarc oxidation, as well as for scientific studies. Intelligent application and the knowledge bank of the system ensure intelligent choice of the optimum technological parameters of microarc processing, along with automatically controlled synthesis of microarc oxide coatings with specified properties. [ABSTRACT FROM AUTHOR]

Complex salt solution systems are commonly used as electrolytes for microarc oxidation (MAO). To investigate the MAO phenomenon in simple electrolytes and evaluate the efficacy of MAO coatings, an Na3PO4 monosalt solution was used as the MAO electrolyte. In this study, the effects of the voltage and Na3PO4 concentration on the spark discharge phenomenon, thickness, roughness, and corrosion resistance of the coatings were investigated. The results showed that MAO coatings were effectively synthesised at high concentrations and voltages. Furthermore, the addition of KOH to the Na3PO4 monosalt solution resulted in discernible spark discharge and improved the corrosion resistance of the coatings. Thus, an MAO coating can be efficiently prepared using Na3PO4 solution as the electrolyte. In addition, the addition of KOH to the Na3PO4 monosalt solution reduced the voltage required for coating formation and enhanced the corrosion resistance of the coating. [ABSTRACT FROM AUTHOR]

This article presents a hypothesis, phenomenological and mathematical models of the exhaust gas neutralization process of an internal combustion engine inside the combustion chamber. The neutralization of exhaust gasses is estimated from surface catalytic properties of the coating, formed on the surface of the combustion chamber parts by microarc oxidation. Phenomenological and mathematical models of the exhaust gases neutralization process in the combustion chamber were developed. Phenomenological model of neutralization process is based on particle diffusion into the surface layer of the coating. Mathematical model is based on Fick's first law and takes into consideration great amount of factors, which affect the process of neutralization: geometrical dimensions and operating characteristics of the engine; properties of coating and exhaust gasses composition. Verification of developed mathematical model was shown in this work. During verification, experimental data, acquired using motor tests of two-stroke 2-cylinder engine RMZ-551 was applied. Calculations were done for the most indicative operating mode of the engine, in which the highest effect of neutralization can be observed. A comparative analysis of the calculated and experimental data was carried out using the concentrations of the CO and NOx components. Calculated values, acquired with the developed mathematical model, differ from experimental values of concentration decrease of previously said exhaust gasses components by 23.3 and 30.4%, respectively. It shows that presented mathematical model could be used for obtaining computational high convergence results. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The structure, phase composition, microhardness, and adhesive strength of a coating on an МЛ10 (ML10) magnesium alloy modified with Mg2SiO4 forsterite during microarc oxidation (MAO) have been studied. Sodium silicate additives were used as a forsterite precursor. A pattern has been established that reflects the minimum concentration of sodium silicate in the electrolyte composition, at which silicon compounds participate in the formation of a ceramic coating on magnesium and are introduced into it, forming complex compounds (Mg2SiO4). With the chosen MAO parameters and the basic composition of the electrolyte, the modification with silicon compounds begins with a concentration of sodium silicate in the electrolyte of 4 g/l. It has been established that at this concentration, a developed interface is formed, which increases the adhesive strength of the coating. In addition, the presence of forsterite in the coating leads to an increase in the thickness and microhardness of the coating.

This article provides the results of corrosion resistance tests of nanostructured oxide-ceramic coatings produced by microarc oxidation on aluminum alloys in a boric acid electrolyte. The coatings were formed on a microarc oxidization plant used in anode-cathode mode. Accelerated corrosion tests were conducted by alternating the immersion of the specimens in sodium chloride solution with their drying in the air. At the microarc oxidation of aluminum alloys in a boric acid electrolyte, the corrosion levels directly depend on microarc oxidation mode and chemical composition of oxidated alloys. At a density of 10–20 A/dm2, continuous corrosion is observed, whereas at a current density of 20–30 A/dm2 staining is observed, which is caused by the fact that corrosive medium penetrates through the pores and produces poultice corrosion. The oxide ceramic coatings on D16 alloys exhibit a weaker resistance to corrosion than on AMg2 and AD1 alloys. It has been established that the corrosion values of aluminum alloys with nanostructured oxide-ceramic coatings are severalfold as low as in uncoated alloys. [ABSTRACT FROM AUTHOR]

The effect of the duration of the microarc-oxidation process on the thickness, roughness, and optical characteristics (solar absorbance αs and emissivity ε) of white and black thermal-control coatings formed on an aluminum alloy AMg6 is studied experimentally. It is found that αs decreases with an increase in the thickness of the coatings with increasing microarc-oxidation-treatment duration. For the white coatings, a decrease in their roughness is accompanied by an increase in ε, and vice versa. For the black coatings, the main role is played by the emissivity factor of the coating, which is determined by the content of vanadium oxide in it. A comparative analysis of the optical characteristics of thermal-control coatings obtained using the microarc-oxidation process on various aluminum alloys show that it is better to form white coatings of the solar-reflector class on aluminum alloy AMg3 and black coatings of the true-absorber class on an aluminum alloy AMg6 with a microarc-oxidation (MAO) treatment duration of 25 min. The obtained experimental data can serve as a framework for the development of a basic technology for the formation of thermal-control coatings on products made of aluminum alloys. [ABSTRACT FROM AUTHOR]

Microarc Oxidation (MAO) technology can prepare a ceramic-like oxide coating. It is an effective technique to increase the wear and corrosion resistance of magnesium alloys. The MAO coating has many defects such as holes and cracks. As well, the coating on magnesium alloys typically consists mainly of MgO, which absorbs water or dissolves in a humid or acidic environment. Therefore, the MAO coatings are not adequate for the long-term protection of magnesium alloys. MAO coatings that are composed of ZrO2, or which have ZrO2 with a compact microstructure, can improve the protection of magnesium alloys. This paper critically summarizes the progress of MAO coatings containing ZrO2 on magnesium alloys from four aspects: electrolyte compositions, electrical parameters, the two-step MAO process, and post-treatment of MAO coating. The future research directions for MAO coatings containing ZrO2 on magnesium alloys are discussed. [ABSTRACT FROM AUTHOR]

Copyright of Electroplating & Finishing is the property of Electroplating & Finishing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aluminum alloys, along with positive properties - low density, high specific strength, electrical conductivity, ductility, viscosity and others, have disadvantages: low hardness, modulus of elasticity, wear resistance and high chemical activity in many inorganic acids. The method of microarc oxidation (MАO) can eliminate these shortcomings. The transformation of the surface layers of the workpiece into high-temperature oxides of aluminum will strengthen the surface and increase its protective properties. The properties of MАO coatings depend on many factors, one of which is the composition of the electrolyte. According to the literature, the most widely used alkaline-silicate electrolytes, which have shown the greatest efficiency in MАO of aluminum alloys. The data available in the literature on the use of multicomponent electrolytes containing sodium aluminate NaAlO2 and sodium hexametaphosphate Na6P6O18 do not allow to elucidate their role in the formation of MАO coatings. Studies of the use of hexametaphosphate to alkaline silicate electrolyte have shown that Na6P6O18 promotes the formation of a thicker coating. The rate of thickness formation in the absence of hexametaphosphate is 0.5 ,7 0.7 μm / min, and at a hexametaphosphate content of 10 g / l - 0.9 ÷ 1.1 μm / min. As for the effect on the phase composition, the effect was not detected. It was studied that the addition of aluminate-silicate electrolytes of sodium aluminate in the amount of up to 13 g / l does not have a significant effect on the thickness of the coating, but affects the phase composition of the coating.

• MAO formed the antibacterial porous oxide layers on Ti surfaces. • Antibacterial porous oxide layers inhibited the growth of MRSA. • Antibacterial porous oxide layers promoted bone formation in vivo. • MAO achieved a balance between antibacterial activity and bone formation on Ti surface. Ti surfaces must balance bone formation and antibacterial activity to achieve bone reconstruction and prevent infections. In this study, a Ti surface was electrochemically modified via micro-arc oxidation in an electrolyte containing calcium ions, phosphate ions, and either Ag, or Cu ions to form an antibacterial porous oxide layer on Ti surface. The resultant porous oxide layers consisted of both electrolyte and substrate elements. The Ag- and Cu-incorporated porous oxide layers exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus. Furthermore, animal experiments were performed to reveal the bone-formation on the Ag- and Cu-incorporated porous oxide layers. Both porous oxide layers promoted bone formation more effectively than untreated Ti. Thus, the Ag- and Cu-incorporated porous oxide layers formed on the Ti surface by micro-arc oxidation balanced bone formation and antibacterial activity owing to their structural and compositional features. Our findings will be useful for the surface design of Ti-based medical devices and can provide a simple electrochemical treatment to form porous surfaces to balance antibacterial activity and bone formation on Ti surfaces. [ABSTRACT FROM AUTHOR]

Abstract Background Microarc oxidation (MAO) on the surface of medical pure titanium can improve its histocompatibility, and loading drugs on the surface can resist excessive intimal hyperplasia. Methods In this study, salidroside (SAL) was loaded on the surface of porous titanium (Ti) with polydopamine (PDA) carrier. The effects of SAL on the osteogenesis and angiogenesis of Ti implants were studied by phalloidin staining, alizarin red staining, ALP staining, wound-healing assay, cell transwell assay, matrigel tube formation, and osteogenic and angiogenic genes and proteins expression detected by PCR and western blot in vitro. The bone defect model experiments in rats was established in vivo including X-ray, micro CT, hematoxylin and eosin staining (HE), immunohistochemistry (IHC), Goldner's trichrome analysis, Safranin O-fast green staining and determination of contents of TNF-α and IL-6 in serum. Results EDS and EDS mapping showed that SAL could be loaded on the surface of the MAO coating by PDA. A drug release experiment showed that SAL loaded on the Ti coating could release slowly and stably without sudden release risk. In vitro cell experiments showed that the SAL coating could promote the proliferation, morphology, calcification and alkaline phosphate activity of MC3T3-E1 cells. At the same time, it promoted the migration and tube formation of HUVEC cells. The SAL coating promoted osteogenesis and angiogenesis by promoting the expression of genes and proteins related to. In vivo experiments, HE and IHC showed that SAL significantly promoted the expression of COL-1 and CD31. Goldner's trichrome and Safranin O-fast green staining showed that SAL coating could increase the new bone tissue around the implantation site. The SAL coating had anti-inflammatory activity by reducing the levels of TNF-α and IL-6 in vivo. Conclusion Therefore, SAL could improve osteogenesis and angiogenesis in conjunction with the Ti-PDA coating.

Background. The object of the study is ceramic-like coatings formed by microarc oxidation on details made of valve metal alloys. The subject of the study is the processes of formation of the structure and properties of ceramic-like coatings when they are obtained without the use of traditional electrolytic baths in the internal cavities of special counter electrodes. The purpose of the study is to establish the possibility of obtaining highquality ceramic-like coatings on compact details made of valve metal alloys. Materials and methods. During the research, ceramic-like coatings were used on spherical, cylindrical and flat surfaces of details made of AMg3 and VT5 alloys, in which thickness and hardness were measured using a PMT-3M micro hardness tester. Results. Studies have found that the thickest and most uniform coatings are formed in the cavities of the counter electrodes corresponding to the shape of the oxidized details, but exceeding the corresponding external dimensions of the details by 8-20 mm, with the flow rate of the solution passing through the counter electrodes 4-10 liters per minute per 1 dm2 of the oxidized surfaces of the detailss with the mandatory change in the direction of the flow of the solution to the opposite after half processing time. Conclusions. Microarc oxidation of compact details made of valve metal alloys in the internal cavities of the counter electrodes ensures the formation of more uniform ceramic-like coatings on them compared to traditional technology. Micro-arc oxidation of valve metal alloy details in the cavities of counter electrodes requires a smaller production area, is associated with a lower risk of harm to health, can be implemented without exhaust ventilation, water cooling and emergency power outage, but requires special equipment.

With the aim of further enhancing the bioactive performance of Ti–6Al–4V, ultrasonic‐assisted microarc oxidation (MAO) and hydrothermal (HT) treatments are combined to produce denser, more uniform hydroxyapatite (HA) crystals on the MAO coating herein. More Ca elements can be deposited on the coating and more TiO2 can be generated to form a thicker coating via ultrasonic assistance. Meanwhile, the MAO coating with ultrasonic assistance avoids the appearance of heterogeneous areas and homogenizes the distribution of elements. Those positive effects of ultrasonic‐assisted MAO coating provide favorable conditions for the subsequent HT treatment to form dense and uniform HA crystals. In vitro experiment shows that the ultrasonic‐assisted MAO coating has a higher number of MG63 cells compared with other samples. Moreover, the formation of HA crystals improves the biological activity of all samples. In the ultrasonic‐assisted sample after HT treatment, denser and more uniform HA crystals on the coating surface result in the higher alkaline phosphatase activity of the sample. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microarc oxidation (MAO) is an effective surface treatment method for Ti alloys to allow their application in extreme environments. Here, binary electrolytes consisting of different amounts of sodium phosphate and sodium silicate were designed for MAO. The surface morphology, composition, and properties of MAO coatings on Ti−6Al−4V alloy treated in 0.10 mol/L electrolyte were investigated to reveal the effect of PO43− and SiO32− on the growth kinetics of the MAO coatings, using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and potentiodynamic polarization. The results showed that PO43− is beneficial for generating microarcs and forming pores within the coating, resulting in a thick but porous coating. SiO32− facilitates the blocking of pores in the outer deposition layer and impedes the generation of microarcs, resulting in a thin dense coating. The thickness, density, phases content, and polarization resistance of the MAO coatings are primarily affected by the intensity of microarcs for low SiO32− contents, and by the number of microarcs when the SiO32− content is sufficiently high. The thickness of MAO coatings obtained in P/Si electrolytes shows a piecewise linear increase with increasing process time during the three stages of microarc discharge. SiO32− is beneficial to the density increase of the coating formed in the previous stage of microarcs discharge, but slows down the growth of the coating formed in the next stage. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance of 7075 aluminum alloy microarc oxidation (MAO) coating, graphene of 3 g/L was adsorbed and deposited in the coating. Then, the microarc oxidation–sol–gel (MAO-SG) composite coating was obtained by sealing the micropores of the coating with TiO2 sol–gel. Electrochemical tests of 7075 aluminum alloy matrix, undoped sample, doped graphene sample and sealed sample were carried out in 3.5wt.% NaCl solution. The results show that compared with the blank sample, the self-corrosion potential of the sealed sample is increased by 98.1%, and the self-corrosion current density is reduced by 4 orders of magnitude. After immersion corrosion for 720 h, the corrosion rate of MAO-SG composite coating is 3.4 × 10–5 mm/a, and its corrosion resistance is still better than that of single MAO coating. This is due to the strong conductivity of graphene and the blocking effect of TiO2 sol–gel. [ABSTRACT FROM AUTHOR]

The purpose of this study was to establish a mechanical and histological basis for the development of biocompatible maxillofacial reconstruction implants by combining 3D-printed porous titanium structures and surface treatment. Improved osseointegration of 3D-printed titanium implants for reconstruction of maxillofacial segmental bone defect could be advantageous in not only quick osseointegration into the bone tissue but also in stabilizing the reconstruction. Various macro-mesh titanium scaffolds were fabricated by 3D-printing. Human mesenchymal stem cells were used for cell attachment and proliferation assays. Osteogenic differentiation was confirmed by quantitative polymerase chain reaction analysis. The osseointegration rate was measured using micro computed tomography imaging and histological analysis. In three dimensional-printed scaffold, globular microparticle shape was observed regardless of structure or surface modification. Cell attachment and proliferation rates increased according to the internal mesh structure and surface modification. However, osteogenic differentiation in vitro and osseointegration in vivo revealed that non-mesh structure/non-surface modified scaffolds showed the most appropriate treatment effect. 3D-printed solid structure is the most suitable option for maxillofacial reconstruction. Various mesh structures reduced osteogenesis of the mesenchymal stem cells and osseointegration compared with that by the solid structure. Surface modification by microarc oxidation induced cell proliferation and increased the expression of some osteogenic genes partially; however, most of the markers revealed that the non-anodized solid scaffold was the most suitable for maxillofacial reconstruction. [Display omitted] • Cellular responses and osseointegration of anodized 3D printed titanium implants with various mesh structures were compared. • Anodization may inhibit osteoclastogenesis. • Non-anodized solid scaffold was most suitable for maxillofacial reconstruction in terms of osseointegration. [ABSTRACT FROM AUTHOR]

The effects of high- and low-frequency coupled square wave pulses and concentration of TiC on TiC/Al2O3 coatings were determined through microarc oxidation on 6063 aluminum alloy. Scanning electron microscopy results showed that the "stack" of micropores and the thickness increased with the increase in TiC concentration and high-frequency pulse amplitude. X-ray diffraction and x-ray photoelectron spectroscopy results showed that the composite coatings primarily consisted of γ-Al2O3, α-Al2O3, TiC, and Al2SiO5. The TiC content increased, the surface hardness of the coatings improved from 781.5 to 1321.4 Hv, and the corrosion current density decreased from 1.497 × 10−6 to 8.979 × 10−10 A cm−2. The friction coefficient decreased from 0.52 to 0.41 at the TiC content of 3 g/L and high-frequency pulse amplitude of 30 V. The TiC content and high-frequency pulse amplitude improved the corrosion and friction performance of the TiC/Al2O3 coatings. [ABSTRACT FROM AUTHOR]

Objective To prepare a copper-nobium antibacterial coating on a titanium surface by a microarc oxidation-microwave hydrothermal two-step method and to study its surface structure and antibacterial properties. Methods Using titanium coated with a microarc oxidation coating (MAO group) as the substrate, copper and niobium were introduced by a microwave hydrothermal method in low (MHL-Cu group), medium (MHM-Cu group) and high (MHH-Cu group) copper chloride solutions and niobium oxalate (MH-Nb group) solutions, respectively. The component with the highest copper content was determined by energy spectrum analysis, and the copper-niobium composite coating (MH-Cu/Nb group) was prepared by microwave hydrothermal mixing with niobium oxalate. The microstructure, element distribution and phase composition of the specimens were characterized by scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction, and the bacteriostatic effect of the coating onEscherichia coliand Staphylococcus aureus was determined by the film method. Results Energy dispersive spectrometry showed that Cu was introduced onto the surface of the MHL-Cu, MHM-Cu, and MHH-Cu groups, and the atomic ratios of copper in each group were （0.68 ± 0.04）%,（1.17 ± 0.06）%, and （1.64 ± 0.03）%. The difference between groups was statistically significant (P< 0.01). Scanning electron microscopy showed a crater-like porous structure on the surface of the MAO group, and the MHL-Cu, MHM-Cu, MHH-Cu, MH-Nb, MH-Cu/Nb groups maintained micropore morphology. The roughness increased with increasing Cu2+ concentration, in which the MH-Nb and MH-Cu/Nb groups showed gully like structures simultaneously. X-ray diffraction showed that the coating of the MAO group was mainly composed of titanium and anatase phase TiO2, and the coatings of the MHL-Cu, MHM-Cu, MHH-Cu, MH-Nb, MH-Cu/Nb groups were mainly composed of anatase and rutile phase TiO2. Compared with the MAO group, Escherichia coli and Staphylococcus aureus in the MHH-Cu, MH-Nb, MH-Cu/Nb groups decreased to varying degrees, with significant differences (P< 0.001); compared with the MH-Cu/Nb group, the colony number difference had statistical significance (P> 0.05).Conclusion The rough, porous coating containing copper and niobium prepared by the microarc oxidation-microwave hydrothermal two-step method can effectively inhibit the growth ofEscherichia coli and Staphylococcus aureus.

Si3N4/TaC composite MAO coatings were fabricated by microarc oxidation (MAO) on a Ti–6Al–4V (TC4) alloy in a phosphate-based electrolyte containing Si3N4/TaC mixed particles. The influence of the amount of Si3N4/TaC particles on the microstructure, composition, tribological behavior, and corrosion properties of the MAO coatings has been investigated. Morphological research of the MAO coatings was carried out using scanning electron microscopy (SEM), with the surface porosity analyzed by ImageJ software. X-ray diffraction (XRD) was used for the detection of the phase characteristic of the MAO coatings, and an abrasive wear test and electrochemical measurements were conducted in the artificial seawater solution by the ball-on-disc friction tester and the electrochemical workstation, respectively. The results showed that Si3N4/TaC particles could be successfully incorporated into the composite coatings, and the addition of Si3N4/TaC particles greatly reduced the porosity of the coatings, thus improving both tribological and corrosion properties of the composite MAO coatings. The composite MAO coating with the addition of 1 g/L Si3N4 + 0.5 g/L TaC particles showed the best tribological property and the optimum corrosion properties. [ABSTRACT FROM AUTHOR]

Abstract Due to their excellent mechanical properties and good biocompatibility, titanium alloys have become a popular research topic in the field of medical metal implants. However, the surface of the titanium alloy does not exhibit biological activity, which may cause poor integration between the interface of the titanium implant and the interface of the bone tissue and subsequently may cause the implant to fall off. Therefore, surface biological inertness is one of the problems that titanium alloys must overcome to become an ideal orthopedic implant material. Surface modification can improve the biological properties of titanium, thereby enhancing its osseointegration effect. Copper is an essential trace element for the human body, can promote bone formation and plays an important role in maintaining the physiological structure and function of bone and bone growth and development. In this study, a microporous copper-titanium dioxide coating was prepared on the surface of titanium by microarc oxidation. Based on the evaluation of its surface characteristics, the adhesion, proliferation and differentiation of MC3T3-E1 cells were observed. A titanium rod was implanted into the rabbit femoral condyle, and the integration of the coating and bone tissue was evaluated. Our research results show that the microporous copper-titanium dioxide coating has a nearly three-dimensional porous structure, and copper is incorporated into the coating without changing the structure of the coating. In vitro experiments found that the coating can promote the adhesion, proliferation and differentiation of MC3T3-E1 cells. In vivo experiments further confirmed that the titanium copper-titanium dioxide microporous coating can promote the osseointegration of titanium implants. In conclusion, copper-titanium dioxide microporous coatings can be prepared by microarc oxidation, which can improve the biological activity and biocompatibility of titanium, promote new bone formation and demonstrate good osteoinductive properties. Therefore, the use of this coating in orthopedics has potential clinical application.

A reliable, high-performance coating procedure was developed using PDMS to modify a duplex MAO/DLC coating on an AZ31B Mg alloy. First, the duplex MAO/DLC coating was fabricated via a combined MAO and unbalanced magnetron sputter process. Subsequently, a PDMS solution was used to modify the MAO/DLC coating via a conventional dip-coating method. The surface characteristics, bond strength, hardness, tribological behaviour, and corrosion resistance of the coated samples were evaluated via SEM, CA, Raman spectroscopy, friction and wear behaviour, polarisation curve, and NSS tests. The PDMS modification reduced the HIT of MAO/DLC coating from 15.96 to 8.34 GPa; this is ascribed to the penetration of PDMS, which has good rheological properties to form a viscoelastic Si-based organic polymer layer on the MAO/DLC coating. However, the PDMS-modified MAO/DLC coating was denser, hydrophobic, and had higher bond strength compared with MAO- and MAO/DLC-coated samples. Moreover, the PDMS modification reduced the COF and wear rate of the duplex MAO/DLC coating. This indicates that the PDMS improved the tribological behaviour owing to the transferred Si oxide that originated from the Si-O network of the PDMS, as well as the low graphitisation of the DLC layer during sliding. Furthermore, the corrosion current density of the MAO/DLC-coated sample modified by PDMS for 10 min decreased by two order of magnitude compared with that of the MAO/DLC-coated sample but by five orders of magnitude compared with that of the bare substrate. The NSS tests proved that the PDMS layer slowed the corrosion of the Mg alloy under long-term service, enhancing the corrosion protection efficiency. The results are attributed to the high bond strength and lubricant MAO/DLC layer, and the dual role of sealing and hydrophobicity of PDMS. Therefore, PDMS modification is promising for the fabrication of protective materials for Mg alloys that require corrosion and wear resistance.

Self-healing polyurethane is widely applied as the anti-corrosion coating to elongate the durability of substrate. However, it remains great challenge to achieve the rapid self-healing performance at room temperature for polyurethane. And it is even more difficult to accomplish the healing under the water. Herein, a novel self-healing polyurethane, PDMS-SS-Py, is prepared to achieve self-healing within 2 h at room temperature. Even under the water, the 97.1 % self-healing efficiency is kept. Molecular dynamics (MD) simulation and density function theory (DFT) demonstrate that hydrogen bonds are pioneers in the healing process of PDMS-SS-Py and elucidate the critical items to achieve the underwater self-healing. On the basis of PDMS-SS-Py, the composite coating, MAO/8-HQ/P, is fabricated on Mg alloy along with microarc oxidation (MAO) and inhibitor 8-hydroxyquinoline (8-HQ) inserted in the micropores of MAO. The self-healing performance of composite coating is almost the same as that of isolate PDMS-SS-Py. As compared with bare Mg alloy, the impedance modulus at the low frequency (|Z| 0.01Hz) is increased by 8 orders of magnitude after covering MAO/8-HQ/P coating. Even after 12 days of immersion in 3.5 wt% NaCl solution, the MAO/8-HQ/P composite coating still maintains superior anti-corrosion performance. The excellent anti-corrosion performance is contributed by the self-healing property of PDMS-SS-Py layer, the active protection of 8-HQ, and the basic protection of MAO. This work provides a general strategy for constructing durable self-healing anti-corrosion coating on Mg alloy and deepens the mechanism of polyurethane repairing processes. [Display omitted] • MAO/8-HQ/P composite coating has superior self-healing and long-term anti-corrosion properties. • PDMS-SS-Py polymer achieves self-healing within 2 h. • Self-healing mechanism is analyzed by MD simulations and DFT calculations. [ABSTRACT FROM AUTHOR]

Spark discharge phenomenon in solution is a typical characteristic in metal microarc oxidation (MAO) surface treatment, and the optical emission spectroscopy (OES) is an effective way of characterizing micro-discharge optical emission spectra and studying the MAO mechanism. In this paper, the research status of OES analyses in MAO process of Al, Mg, Ti and their alloys was reviewed, the calculation principle of electron temperature and density in microarc plasma discharge channels was introduced, and the influence of the plasma discharge behavior on the microstructure of MAO coatings at different metals, electrical parameters and electrolyte solutions was evaluated. Furthermore, the different discharge models on the basis of OES analyses were also discussed. The plasma temperature in microarc discharge zone for different metals calculated from OES was in the range of 3000 - 10000 K, which provided the evidence for the growth mechanism of ceramic coatings enhanced by quick molten-solidification process in discharge channel.

Peri-implantitis and insufficient osseointegration are the principal challenges faced by dental implants at present. In order to fabricate dual-function dental implant materials possessing both antibacterial and osteogenic capabilities, this study incorporates the antimicrobial element Cu into the Ti40Nb alloy, developing a novel Ti40Nb-xCu alloy with antibacterial properties. Among them, Ti40Nb3Cu has the best overall performance. Compared to Ti40Nb, the tensile strength increased by 27.97%, reaching 613 MPa. Although the elongation rate has decreased from 23% to 13.5%, the antibacterial rates against S. aureus and P. gingivalis both exceed 85%. Furthermore, the surface of Ti40Nb-xCu alloy was then treated with micro-arc oxidation to enhance its bioactivity, thereby accelerating osseointegration. The results indicated that the MAO treatment retains the antibacterial properties of the Ti40Nb3Cu alloy while significantly promoting bone formation through its introduced porous coating, thus heralding it as a propitious candidate material for dental implant applications. • Novel Ti–40Nb-xCu alloy with bacterial inhibitory property is developed. • Comprehensive performances of Ti–40Nb-xCu alloy are systematically investigated. • The Ti40Nb–3Cu alloy, treated with MAO, possesses excellent antibacterial properties and bone-forming capabilities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inherent micropore-cracks on the MAO surface are eliminated by the femtosecond laser; • The alumina nanocrystallines (γ-Al 2 O 3 and α-Al 2 O 3) are formed and embedded into the original amorphous layer; • Material surface becomes the intrinsically superhydrophobic even at high temperatures; • The measured corrosion current falls to an unprecedent value of 1.46 × 10-13 A/cm2. Microarc oxidation (MAO) is a widely employed technology for the corrosion protection of metal surfaces due to the formation of thick-layer ceramic substances. However, its practical effectiveness is strictly limited by the inevitable concomitant generation of numerous microscale pores/cracks on the oxidation surface to directly expose the substrate materials. As concerning this problem, we here introduced a novel method of the femtosecond laser irradiation to completely eliminate the above MAO defects on aluminum alloys, which consequently modulates the passivation layer into the dense and the superhydrophobic. Meanwhile, with the deep insights into the phase composition variations of the oxide layer, we can find that the laser treatments enable the development of both γ-Al 2 O 3 and α-Al 2 O 3 nanocrystallines with embedment in the amorphous substances to significantly improve the chemical stability of materials. Such laser modifications eventually result in the ultra-corrosion-resistant surface of aluminum alloys, with the measured corrosion current density of 1.46 × 10-13 A/cm2 as well as the impedance value over 112 GΩ∙cm2, about two orders of magnitude enhancement in the anticorrosion compared to the initial MAO sample. [ABSTRACT FROM AUTHOR]

The presence of pores in a microarc oxidation (MAO) coating is an inherent characteristic that results from the expulsion and rapid solidification of molten material during the MAO process. The pore size in the MAO coating on the titanium alloy strongly affects the biocompatibility, but how to control it is unclear. The present study utilizes the advantages of NaOH to modulate pore size and plasma discharge, thereby effectively regulating the pore structure of the coating. The FIB-lift-out method was employed to directly extract the cross-sectional samples from the coating, enabling a detailed investigation of the pore microstructure using transmission electron microscopy (TEM). The structure surrounding the discharge channels exhibit layered zoning characteristics, with an amorphous layer near the discharge channel and a distinct crystal structure further away from it. The addition of NaOH enables the regulation of electrochemical and energy release processes, while also facilitating efficient discharge and spark generation to effectively disrupt the oxide layer and establish a plasma discharge channel. The presence of pores in a microarc oxidation (MAO) coating is an inherent characteristic resulting from the expulsion and rapid solidification of molten material during the MAO process. The pore size of the MAO coating on the titanium alloy strongly affects the biocompatibility, but how to control this effect is unclear. The present study utilizes the advantages of NaOH to modulate pore size and plasma discharge, thereby effectively regulating the pore structure of the coating. The FIB-lift-out method was specifically employed to directly extract cross-section samples from the surface of the microarc oxidation coating, enabling a detailed investigation of the pore microstructure using transmission electron microscopy (TEM). The structure surrounding the discharge channel exhibits layered zoning characteristics, with an amorphous main structure near the discharge channel and a distinct crystal structure further away from it. The addition of NaOH ultimately enables the regulation of electrochemical and energy release processes while also facilitating efficient discharge and spark generation to effectively disrupt the oxide layer and establish a plasma discharge channel. [Display omitted] • A porous MAO coating on Ti-6Al-4 V with good biocompatibility is enabled by the addition of NaOH in a silicate electrolyte. • The porosity, pore size and thickness of MAO coatings are regulated by adjusting NaOH concentration. • Distinct layered band characteristics including crystalline and amorphous structure form surrounding the discharge channel. [ABSTRACT FROM AUTHOR]

Corrosion is an inevitable and thorny issue in various fields, resulting in materials degradation, environmental pollution, economic loss, and even emergency safety accidents. Owing to the special surface functions, superhydrophobic coatings are regarded as a promising strategy towards corrosion inhibition. However, the large‐scale and real‐world applications of superhydrophobic coatings are restricted by the mechanical and chemical weaknesses. Herein, a fluorine‐free dual‐layer microarc oxidation/superhydrophobic coating with mechanochemical stabilization is fabricated for corrosion protection. The dual‐layer coating maintains superhydrophobicity under ultraviolet irradiation (15 d), different pH values (1–14), different temperatures (0–100 °C) and abrasion test (180 cycles). Its impedance modulus at the lowest frequency is increased by more than six orders of magnitude than that of the pristine substrate, and the corrosion inhibition efficiency value is calculated as 99.999%. The enhancement of surface multifunctions is attributed to the synergistic effects of microarc oxidation layer and superhydrophobic layer. The as‐prepared robust dual‐layer coating with excellent properties is expected to have potential applications in material protection fields. [ABSTRACT FROM AUTHOR]

An ideal self-sealing hydroxyapatite (HA)-MgO coating was designed on an AZ31 Mg alloy by one-step microarc oxidation (MAO) with the addition of HA nanoparticles into a base electrolyte. The formation mechanism of the self-sealing HA-MAO coating was discussed. The effect of the nano-HA addition on the corrosion resistance of the MAO coating was evaluated by corrosion tests in Hank's solution. The results show that HA nanoparticles inertly incorporated into the MAO coating during the process of coating growth. HA and MgO were the main constituents of the HA-MAO coating. The HA nanoparticles were absent in the inner barrier layer but concentrated in the outer porous layer. In addition, HA nanoparticles accumulated much more inside coating defects than in the other zones, which resulted in the nearly ideal sealing of micropores on the coating surface. By forming a denser and more stable outer layer, the incorporation of HA nanoparticles greatly enhanced the anti-corrosion properties of the MAO coating. [ABSTRACT FROM AUTHOR]

In this study, the 10B21 steel was treated by micro-arc oxidation (MAO) in the electrolyte consisting of aluminate and phosphate to enhance its corrosion resistance. The effect of negative voltage on corrosion resistance of the MAO coating obtained has mainly been analyzed through their phase composition, microstructure, interfacial bonding strength, salt spray and electrochemical testing. The result indicates that with negative voltages applied to the MAO coating, Fe-Al transition layers arise between coating layer and matrix. Furthermore, different negative voltages bring forward different α-Al2O3 contents contained in the MAO coatings and when it reaches −100 V, the amount of α-Al2O3 appears as the largest. The surface porosity of the coating was also significantly decreased. In addition, the corrosion current density of the coating is only 3.64 μA·cm−2, which is two orders of magnitude lower than that of the substrate. After 72 h of salt spray corrosion, it is found that the coating substrate is less corroded when the negative voltage of 100 V is applied. Therefore, −100 V has been proven as the optimum performance for improving the corrosion resistance of 10B21 steel. [ABSTRACT FROM AUTHOR]

Heat transfer and critical heat flux on flat rectangular (16 × 24 mm) heat-releasing surfaces (HS) made of aluminum alloy D16 and modified by microarc oxidation (MAO) were investigated. Two types of coatings made using different electrolytes were studied: KOH and phosphates. Coatings had good adhesion to the HS and high dielectric strength. The thickness of coatings was 20 and 7 µm, respectively. The studies were carried out using freon R21 under conditions of natural convection with horizontal orientation of the HS. For comparison, measurements were carried out on identical test sections without a modifying coating: the first section was polished; the second one was ground with a roughness of 20 µm. It was shown that the heat transfer intensity on the modified HS was not lower than that on the ground HS with a roughness of 20 µm, and it was almost twice as high as that on the polished HS. The values of the critical heat flux on the studied surfaces were almost the same. The use of these types of coatings provides electrical insulation of the heat-releasing element without compromising the efficiency of heat removal. [ABSTRACT FROM AUTHOR]