Micro-arc Oxidation Time Research Articles

Preparation and performance analysis of Ti-25Nb-3Zr-2Sn-3Mo microarc oxidized macro-micro-nano tertiary structure film layers

After undergoing microarc oxidation, titanium alloys exhibit significantly enhanced biocompatibility, making them a subject of extensive research in the field of biomedical applications. In this study, a two-step microarc oxidation method was used to prepare a film layer with both macro-micro-nano tertiary structures on β-type titanium alloy Ti-3Zr-2Sn-3Mo-25Nb (TLM), using a phosphate-nitrate mixed electrolyte for the first step of microarc oxidation and a borate body electrolyte for the second step of microarc oxidation. The effects of NaOH concentration, microarc oxidation voltage, and time on the size and distribution of macropores prepared by microarc oxidation in the first step were investigated by SEM, energy dispersive spectroscopy, XRD, and metallurgical microscopy. The wettability of the prepared three-level structured film and its ability to induce hydroxyapatite deposition were evaluated through contact angle testing and simulated body fluid immersion experiments. The overall research findings indicate that the two-step microarc oxidation process yielded macropores with diameters ranging from 200 to 400 μm, along with micro-nanostructures measuring 2–15 μm and 10–100 nm. The increase in the NaOH concentration in the electrolyte decreased the size of the macropores. The increase in the microarc oxidation time increased the size of macropores; the voltage affected the distribution and number of macropores. The prepared macro-micro-nano tertiary structured membrane layers have excellent wettability and the ability to induce hydroxyapatite precipitation, indicating that they possess good biocompatibility. This study provides a reference for the medical development of alloys.

Undoped and diamond-doped MAO coatings prepared on Ti6Al4V: Microstructure, wear, corrosion, and biocompatibility properties

In order to improve the wear resistance and biocompatibility, undoped and diamond-doped micro-arc oxidation (MAO) coatings are prepared on Ti6Al4V in this paper by using electrolyte without/with diamond nanoparticles. The microstructure, wear resistance, corrosion resistance, and cytocompatibility performance of the coatings are studied and compared. The results show that undoped and diamond-doped MAO coatings have similar surface morphologies and thicknesses. With the increase of the MAO time, the surface morphology of the two types of coatings translates from the micro-sized traditional volcano pores into Micro/Nano-pores composite structure. The diamond-doped MAO coatings have higher wear resistance than the undoped MAO coatings and the original Ti6Al4V substrate. All the MAO coatings have higher corrosion resistance than the Ti6Al4V substrate. However, the diamond doping has no obvious influence on the corrosion resistance. In vitro assays indicate that both the two kinds of MAO coatings have a better ability to enhance the adhesion, spreading, proliferation, and osteogenic differentiation of MC3T3-E1 osteoblasts compared with the original Ti6Al4V substrate. Considering the high wear resistance, the diamond-doped MAO coatings are more promising for Ti6Al4V alloy.

Structure and mechanical properties of MAO coatings formed on aluminum-coated titanium alloy

ABSTRACT Application of titanium alloys is restricted due to their low hardness and poor wear resistance. Duplex surface treatment consisting of depositing of Al coating by arc ion plating (AIP) plus micro-arc oxidation (MAO) was carried out on Ti6Al4V alloy to improve its tribological performance. Ceramic coating mainly composed of α-Al2O3, γ-Al2O3 and mullite was fabricated on the aluminum-coated titanium alloy after the MAO treatment, and its thickness, compactness and hardness increased with the MAO time before the titanium alloy was oxidized. After the substrate titanium alloy was locally oxidized due to oxygen anions inward migration, a thin transition layer containing titanium oxides and aluminum titanate formed and incorporation of Ti in the alumina coating occurred. Occurrence of the strong eruptible discharges at these positions was facilitated probably due to the large difference in permittivity of the alumina and the titanium oxides, which led to the formation of penetrating cracks in the MAO coating. The hardness and compactness of the ceramic coating decreased. Tensile test results showed bonding strength of MAO ceramic coating/aluminum layer/titanium alloy substrate system was more than 40 MPa, and the maximum value could reach around 68 MPa. The bonding strength of the ceramic coating/titanium alloy substrate system decreased to around 34 MPa due to the weak bonding between the alumina ceramic coating and the titanium alloy substrate. Tribological test results show wear resistance of titanium alloy was greatly improved due to the fabrication of hard alumina ceramic coating on titanium alloy.

Preparation and characterization of micro-arc oxidation coating on hollow glass microspheres/Mg alloy degradable composite

Micro-arc oxidation (MAO) coatings on hollow glass microspheres (HGM) reinforced Mg alloy degradable composite were prepared in alkaline silicate electrolyte. The morphology, chemical composition and corrosion resistance of the coatings were investigated by SEM, EDS, XPS, XRD and electrochemical tests. The growth characteristics of the coatings and the effects of HGM on the MAO behavior were specially studied. The results showed that the main compositions of the coatings were MgO and Mg2SiO4 phases. The coatings possessed different growth behaviors on the different areas of the surface. The coatings exhibited faster growth rate on the α phase than the β phase. The HGM and Mg2Si particles hindered the growing of the coating in the early stage of MAO, but they would not disrupt the continuity of the coating, since they were gradually melted, reduced and disappeared, and translated into oxides of silicon and magnesium finally in the MAO process. The average thicknesses of the coatings obtained at MAO time of 10, 20, 30, and 40 min were 2.9 ± 0.9, 10.9 ± 0.8, 20.2 ± 1.2, and 22.7 ± 1.9 μm, respectively. Electrochemical tests showed the MAO coating obtained at MAO time of 30 min possessed the best corrosion resistance, the corrosion current density of which was approximately four orders of magnitude lower than that of the substrate.

Effect of Micro-arc Oxidation Time on Corrosion Resistance of Magnesium Alloys

This experiment investigates the effect of time on the quality of the film during the micro-arc oxidation of magnesium alloys. The micro-arc oxidation surface morphology, the thickness of the film layer, and the influence on the corrosion resistance of the magnesium alloy were studied at different times. The experiment found that when the micro-arc oxidation time is controlled at 9 minutes, the surface quality of the film layer is the best, and the improvement of the corrosion resistance is more obvious.

Effect of Molybdate Conversion Coating of Magnesium Alloy Reinforced by Micro-arc Oxidation

In order to enhance the corrosion resistance of molybdate conversion coating, the molybdate coating is subjected to micro-arc oxidation treatment in electrolyte with Na2SiO3 as a main salt. The electrochemical behavior and corrosion weight loss of different coating were studied. The surface morphology, element composition, roughness and phase composition of different coatings were analyzed by SEM, EDS, laser confocal microscopy and XRD, the growth process of different micro-arc oxidation coatings was explored. The results shows that the arcing voltage of the molybdate coating enhanced by micro-arc oxidation is significantly reduced, the corrosion potential is shifted to the right, and the corrosion weightlessloss of the coating is the lowest, compared with the molybdate coating and the micro-arc oxidation coating. Micro-arc oxidation on the surface of the molybdate coating is beneficial to the formation of MgAl2O4 and the production of new phase is MoSi2, which can better improve the corrosion resistance of the molybdate coating. The micro-arc oxide coating does not form a ceramic film with a pore structure at the moment of arcing. As the micro-arc oxidation time prolongs, the ceramic film is gradually formed. When the time reaches 60 s, the ceramic film is completely formed. In this paper, micro-arc oxidation treatment is performed on the basis of molybdate conversion coating to obtain micro-arc oxidation enhanced molybdate coating. The experiment is mainly divided into three parts: the first part, molybdate conversion treatment of the magnesium alloy substrate to obtain a molybdate conversion coating. The second part, the micro-arc oxidation treatment is performed on the surface of the molybdate coating, and discharge channels appear on the surface. The third part, micro-arc oxidation enhanced molybdate coating is obtained.

Effect of micro-arc oxidation time on coating formation of AZ91 magnesium alloy in silicate electrolyte

The micro-arc oxidation behavior of AZ91 magnesium alloy in silicate alkaline electrolyte was studied. The effects of micro-arc oxidation time on film formation and microstructure were investigated and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), emission spectrometry (ICP) and salt spray test. The results show that oxidation time has an important effect on the surface morphology, thickness, phase structure and corrosion resistance of micro-arc oxidation film. With the increase of treatment time, the surface roughness and pore size increased. The acid ion (SiO3 2-) in electrolyte plays an important role in the formation of phase in the early stage of micro-arc oxidation, and the formation rate of MgO is dominant in the later stage. The corrosion rate decreases first and then increases with the increase of treatment time, and the corrosion rate of the sample processing 30min is lower under our technological conditions.

Fatigue life of micro-arc oxidation coated AA2024-T3 and AA7075-T6 alloys

Two types of aluminum (Al) alloys, namely 2024-T3 and 7075-T6, were treated by micro-arc oxidation (MAO). Microstructure of as-fabricated ceramic coatings was investigated. Furthermore, the effect of MAO time on fatigue life of the coated samples with thin coating was systematically explored. Morphologies of the coating, second phase particles, and distribution of copper (Cu) and Zinc (Zn) in the coating were observed by scanning electron microscopy, confocal laser scanning microscopy, and energy dispersive spectrometry. Residual stress and phase compositions were analyzed by X-ray diffraction. More Cu in 2024-T3 Al alloy promoted formation of the coating; however, surface porosity of the coating was high. Residual stress induced in the coating deposited on AA2024 was compressive in nature. In contrast, the residual stress in the coating prepared on AA7075 was tensile due to the high content of Zn in the substrate. The results of fatigue test showed that fatigue life of the coated AA2024 increased; however, the MAO treatment was detrimental to fatigue performance of the AA7075 compared to uncoated samples. With prolonging oxidation time, the fatigue life of the coated samples first increased and then decreased. The changes of fatigue life were attributed to the residual stress, coating defects including micro-pores and micro-cracks, and second phase particles in the Al alloy substrate.

Effect of micro-arc oxidation time and applied voltage on formation of strontium- and silicon-incorporated biocoatings

The study of the influence of the MAO time and applied voltage on the formation of the structure, phase and elemental compositions, and properties of Sr-Si-CaP coatings on the titanium surface were performed. It was established that the coating thickness, roughness and the average size of the structural elements (spheres and pores) grow linearly with increasing of the MAO voltage from 200 to 370 V. While, the MAO time effects only on the coating thickness. XRD revealed that the coatings deposited at the low voltages of 200-250 V have X-ray amorphous structure. Increase of the voltage to 350 V leads to the formation in the coatings of crystalline-amorphous structure with amount of crystalline monetite (CaHPO4) phase to 35±5 wt.%. The EDX microanalysis showed that maximum Ca/P atomic ratio of 0.9 and maximum contents of 1.0 at.% Sr and 1.2 at.% Si were found on the coating surface in the regions of accumulation of the monetite crystals for the coatings deposited at high voltages of 300-350 V.

Preparation of Antibacterial Ceramic Coatings Containing Ag on Titanium Alloy by Use of Microarc Oxidation

This paper attempts to utilize the two-stage method of microarc oxidation (MAO) and then the cathodic reduction method to prepare silver element contained in titanium oxide coating. The effects of MAO voltages, reduction voltages, and time on the surface morphology, silver content, and antibacterial and bioactivity properties of the coatings are investigated. The results show that the quantity of bacteria lessened around titanium oxide coating with silver contained. Furthermore, the higher the silver content is, the lesser the number of bacteria around.

The technology of preparing green coating by conducting micro-arc oxidation on AZ91D magnesium alloy

Abstract Micro-arc oxidation was applied to AZ91D magnesium alloy by taking K2Cr2O7 as the colouring salt in the silicate system. It was shown that the green coating obtained through performing micro-arc oxidation on magnesium alloy consisted of Mg, Mg2SiO4, MgO, and MgCr2O4 based on analysis of X-ray diffraction (XRD), and scanning electron microscopy (SEM). Among which, MgCr2O4 was the colouring salt; there were something in the lamellar, pit, and convex forms found on the surface of the coating. The coating consisted of a porous, and a compact, layer from the outside to the inside. As demonstrated, the colour of the coating depended on the K2Cr2O7 concentration: it became gradually deeper with the addition of K2Cr2O7 and the increasing micro-arc oxidation time. The corrosion resistance and hardness of the green coating were greater than that of the matrix.

Effect of anodizing time on the mechanical properties of porous titania coatings formed by micro-arc oxidation

Porous TiO2 coatings were produced on commercially pure Ti substrates by micro-arc oxidation (MAO) in 1.0M H2SO4 electrolyte for different anodizing times. Their mechanical properties were assessed by means of instrumented indentation, XRD residual stress measurements and scratch resistance tests. The rutile/anatase ratio increased from ~0 up to 84% in the 10–360s anodizing time range, with further increase of coating thickness, porosity and roughness. Titania coatings produced for 180 and 360s had poor adhesion and uneven surfaces with spontaneous detachment from the substrate. Coating hardness ranged from 3.5 up to 4.0GPa (close to Ti), whereas the effective elastic modulus varied from 110 up to 120GPa (19% lower than Ti), regardless of the substrate effects. Coatings exhibited tensile residual stresses, while the substrate compressive stress increased forming a plateau at about −110MPa for anodizing time longer than 60s. The presence of such hardened layer beneath the interface improved the coating integrity in the scratch tests under the severe tribological condition, thereby increasing about tenfold the detachment critical load for the samples prepared in the 10–60s MAO time range. Therefore, the 60s anodizing time can be a useful reference line for producing mechanically resistant porous titania coatings.

Zn and Ag Co-doped Anti-microbial TiO2 Coatings on Ti by Micro-arc Oxidation

Micro-porous TiO 2 coatings co-doped with Zn 2+ and Ag nanoparticles were fabricated on Ti by micro-arc oxidation (MAO) for 0.5, 1.5, 2 and 4 min, respectively. The evolutions of morphology and phase component of the coating as a function of processing time were investigated. The microstructure of the 2 min treated coating was further observed by transmission electron microscopy to explore the coating formation mechanism. The amounts of Ag and Zn released from the 2 min treated coating were measured and the antibacterial properties of the coatings against Staphylococcus aureus ( S. aureus ) were also investigated. The obtained results showed that with prolonged MAO time, the contents of Ag and Zn on the coating surfaces increased. All the coatings were micro-porous with pore diameters of 1–4 µm; however, some pores were blocked by deposits on the 4 min treated coating. The 2 min treated coating was composed of amorphous TiO 2 , anatase, rutile, ZnO, Zn 2 TiO 4 and homogenously distributed Ag nanoparticles. After immersion, Zn 2+ , Ag + , Ti 2+ and Ca 2+ were released from the coating and with the immersion time prolonged, the accumulated concentrations of these ions increased. After immersion for 36 weeks, the accumulated Zn 2+ and Ag + concentrations were 6.88 and 0.684 ppm, respectively, which are higher than the minimal inhibitory concentration but much lower than the cytotoxic concentration. Compared with polished Ti control, the coatings co-doped with Zn 2+ and Ag nanoparticles significantly inhibited the adhesions of S. aureus and reduced the amounts of planktonic bacteria in culture medium, indicating that the Zn and Ag co-doped TiO 2 could be a bio-adaptable coating for long-lasting anti-microbial performance.

Optimization of electrical parameters for micro-arc oxidation of zirconium hydride alloy

The present work aims to present the micro-arc oxidation (MAO) zirconia coating with superior compactness and moderate thickness on zirconium hydride. The experiments were designed according to L16 (44) orthogonal array to optimize electrical parameters (frequency, negative voltage, positive voltage and MAO time), with four levels of each factor. The optimized value was predicted and verified by the confirmation experiment. The anti-permeation effect was tested by means of vacuum dehydrogenation experiment. The optimized coating parameters are listed as follows: treating time of 25 min, frequency of 200 Hz, negative voltage of 150 V and positive voltage of 380 V. Experimental results show that the optimized coating exhibits the highest compactness of 0.3705 mg·μm−1. This dense coating significantly enhances the hydrogen anti-permeation effects, and the PRF value is improved by nearly 13 times in contrast with that of uncoated ZrH1.8.

Effects of micro arc oxidation on fatigue limits and fracture morphologies of 7475 high strength aluminum alloy

The oxide coatings with thicknesses of 8 μm, 10 μm, and 15 μm were prepared on 7475 aluminum alloy with micro arc oxidation (MAO) by controlling MAO time, the fatigue limits of original and MAO samples were contrastively measured by the Roccati method. The surface-interface morphologies, fracture morphologies, surface phases, and residual stresses of MAO coating were analyzed with a scanning electron microscopy (SEM), X-ray diffractometer (XRD) and XRD stress tester, respectively. The results show that fatigue limits of the MAO samples decreases as the coating thickness increasing. The fatigue limit of MAO sample with thickness of 8 μm, 10 μm, and 15 μm decreases by 6.48%, 8.33%, and 11.11%, respectively, compared with the original sample. The residual stress and defects introduced by MAO were the main factors of decreasing fatigue limits.

Preparation of Sn4+-Doped Titanium Dioxide Photocatalytic Films on 304 Stainless Steel by Duplex Treatment

Sn4+-doped titanium dioxide photocatalytic films were synthesized on 304 stainless steel (SS) by a duplex treatment. The SS substrates were alloyed with titanium (Ti) through cathodic-arc ion plating followed by a microarc oxidation (MAO) treatment in different electrolytes. Field-emission scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy were used to characterize the films surface morphology, crystalline phase, and composition, respectively. Photocatalytic activity was measured using an UV-Vis spectrophotometer. It was found that the films with a porous structure are mainly composed of TiO2, which exists in an anatase and rutile state. Furthermore, small quantities of SnO2 have been found in the Sn4+-doped titanium dioxide films. The fraction of anatase varies with the MAO time and electrolytes, whereas the pore size remains the similar with the same MAO current intensity and density and the surface roughness increases slightly with increasing MAO time. It was also found that the photocatalytic activity of the Sn4+-doped porous film improved, and the film synthesized with a shorter MAO time in a lower Na2SnO3-containing electrolyte is superior to the films with longer MAO times and higher Na2SnO3 concentrations.

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4±0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 μm. Residual stresses attributed to γ-Al2O3 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2ψ method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667±20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.

Study on Properties of Al<sub>2</sub>TiO<sub>5</sub> Coating on Ti-6Al-4V Titanium Alloy

The Al2TiO5Coating was deposited on Ti-6Al-4V alloy substrate by homemade micro-arc oxidation system. The microstructure of Ti-6Al-4V titanium alloy, the phase of coating, the bonding force of the coating and matrix, sulfuric acid corrosion resistance and high-temperature oxidation resistance were study by inverted microscope model, Xray diffract meter, scanning electron microscopy, the coating adhesion automatic scratch tester, box-type furnace. The results show that the phase of coating is composed of Al2TiO5and Al2SiO5, and Al2TiO5.is the main component, the coating surface consists of discharging pit and flange which are unequal in size, rough and overlap and micro-arc oxidation pit diameter increases with the voltage. When micro-arc oxidation voltage is constant, the longer micro-arc oxidation time, the greater the Ti-6Al-4V alloy coating and the substrate binding force. The corrosion resistance of Ti-6Al-4V alloy was improved in sulfuric acid due to micro-arc oxidation; the sulfuric acid corrosion resistance of the coated samples was improved 11 times when the micro-arc oxidation time increased from 5min to 60min. the high-temperature oxidation resistance of Ti-6Al-4V alloy with micro-arc oxidation coatings is higher than Ti-6Al-4V alloy without micro-arc oxidation coating.

A Porous TiO<sub>2</sub> Coating with Vermiform Morphology Formed on Ti through Micro-Arc Oxidation

A porous titania (TiO2) coating with vermiform slots was prepared on the Ti substrate through micro-arc oxidation (MAO) treatment using sodium tetraborate as electrolyte. Morphologies and phase structure were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Results show that the rutile phase increases and anatase decreases gradually with increasing MAO time. The electrolyte of sodium tetraborate has significant influence on the formation of vermiform coatings, which determine the corrosive patterning in the first stage during MAO processing. The evolution of vermiform morphology is proposed as followed: some corrosive pores appear on the surface before arcing; afterward, the adjacent micropores in the dense regions link each other due to the high temperature result from continuous arc action; then, the micropores grow up to big pits and combine with each other with increasing MAO treating time; finally, the vermiform morphology forms on the surface of Ti metal.

Structural characteristics and outward–inward growth behavior of tantalum oxide coatings on tantalum by micro-arc oxidation

The coatings composed of CaTa2O6, Ta2O5 and TaO were formed on pure tantalum by micro-arc oxidation in electrolytic solutions of calcium acetate and β-glycerophosphate disodium using a pulse power supply. The morphologies, phase components, bond strengths and growth behavior of the coatings with increasing the micro-arc oxidation (MAO) time were investigated. The obtained results demonstrate that the coatings are porous without apparent interface to tantalum substrates and can tightly bond to the substrates. The growth of the coatings micro-arc oxidized (MAOed) at 350 and 450V with MAO time exhibits similar outward–inward growth characteristics and contains three stages. At earlier stage of MAO (e.g., from 0 to 1min), there is a dramatic increase in the total thickness and the total growth rate of the MAO coatings, and outward-growth dominates the growth behavior of the coatings. From 1 to 5min, the total thickness of the coatings increases gently and the total growth rate declines sharply; at this stage, the outward growth gradually slows down, and the inward growth maintains persistent enhancement. At later stage of MAO (e.g., from 5 to 15min at 350V and 5 to 20min at 450V), the inward growth plays a predominant role in the growth of the coatings.