Micro-arc Oxidation Treatment Research Articles

Enhanced Surface Properties of TiO2-Based Coatings via Stevia-Assisted Spark Suppression: Insights from Density Functional Theory Calculations

This study investigates the enhancement of surface properties in TiO2-based coatings on the Ti-6Al-4V alloy through micro-arc oxidation (MAO), employing stevia sugar as a novel additive. By incorporating stevia sugar into acetate–glycerophosphate–tetraethoxysilane solutions used in MAO treatment, the porous morphology of TiO2-based oxide layers is regulated. The incorporation of stevia moderates plasma discharge intensity, facilitating the formation of a uniform silicon-rich structure characterized by reduced porosity and pore size. This effect is attributed to the interaction between stevia and tetraethyl orthosilicate (TEOS), which modifies the TEOS hydrolysis process, thereby enhancing structural uniformity and stability while concurrently reducing plasma discharge intensity. Additionally, theoretical calculations offer a valuable understanding of the reactivity and interactions of stevia, TEOS, and their complex during the MAO process, laying the groundwork for further research and optimization in this promising field.

The growth behavior and performance of microarc oxidation coating on AZ91/Ti composite: Influence of Ti-reinforcement phase and electrolyte

Magnesium matrix composites with both high strength and ductility have been achieved by introducing pure Ti particles. However, the properties of the surfaces of the composites need to be improved by surface technology, such as micro-arc oxidation (MAO). In this study, we investigated the influence of the Ti-reinforcement phase on coating growth and evolution by subjecting both AZ91 alloy and AZ91/Ti composite to MAO treatment using silicate-based and phosphate-based electrolytes. Results revealed that the Ti-reinforcement phase influenced the MAO process, altering discharge behavior, and leading to a decreased cell voltage. The vigorous discharge of the Ti-reinforcement phase induced the formation of coating discharge channels, concurrently dissolving and oxidizing Ti-reinforcement to produce a composite ceramic coating with TiO2. The MAO coating on the AZ91/Ti composite exhibited a dark blue macromorphology and distinctive local micromorphological anomalies. In silicate electrolyte, a “volcano-like” localized morphology centered on the discharge channel emerged. In contrast, treatment in phosphate-based electrolyte resulted in a coating morphology similar to typical porous ceramic coatings, with visible radial discharge micropores at the reinforcement phase location. Compared to the AZ91 alloy, the coating on the AZ91/Ti composite exhibited lower thickness and higher porosity. MAO treatment reduced the self-corrosion current density of the AZ91/Ti surface by two orders of magnitude. The silicate coating demonstrated better corrosion resistance than the phosphate coating, attributed to its lower porosity. The formation mechanism of MAO coatings on AZ91/Ti composites in phosphate-based and silicate-based electrolytes was proposed.

Surface aspects of novel Bio-HEAs MAO-treated in a Ca-, P-, and Mg-rich electrolyte

This study evaluated the effect of alloying elements, applied voltage, and bioactive species (Ca, P, and Mg) enrichment during the micro-arc oxidation (MAO) treatment of novel high entropy alloys (HEAs) targeted for biomedical applications. The non-equiatomic TiZrNbTaMo (TaMo), TiZrNbTaMn (TaMn), and TiZrNbFeMo (FeMo) samples were submitted to MAO treatment at distinct voltages (100, 200, and 300 V), then their chemical, phase, and morphological aspects were evaluated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM and TEM). Finally, the preliminary physicochemical behavior regarding contact angle and surface energy in distilled water at room temperature was evaluated. The results indicated that the alloying elements played a global role in the bulk’s phase composition, possessing distinct proportions of BCC and HCP phases. The MAO-treated surfaces depicted different mechanisms of anodic oxide growth and dielectric breakdown, forming the typical porous surface at distinct applied voltages. The bioactive species (Ca, P, and Mg) were gradually enriched in the oxide layer, composed of distinct nano-crystalline and amorphous layers that are typical of MAO-treated surfaces. As a result, roughness, contact angle and surface energy values of the MAO-treated samples were affected by the applied voltage and the bulk’s chemical composition, indicating potential for use in the biomedical field, especially as long-term implants and bone fixation devices.

Micro-arc and thermal oxidized titanium matrix composites for tribocorrosion-resistant biomedical implants

Superior tribocorrosion resistance is offered by titanium matrix composites (TMCs) compared to their unreinforced matrix metal, but bioactivity concerns are raised for biomedical applications. Simple methods such as micro-arc oxidation (MAO) and thermal oxidation (TO) are employed to enhance the bioactivity and degradation resistance of Ti. However, the impact of those surface treatments on TMC surfaces is poorly understood. Therefore, the present work aimed to explore the influence of MAO and TO treatments on the surfaces of in-situ Ti-TiB-TiC and ex-situ Ti-B4C composites, and to assess their corrosion and tribocorrosion performance. Corrosion and tribocorrosion tests were conducted in phosphate-buffered saline solution (PBS) at body temperature. Electrochemical assays were performed by means of potentiodynamic polarization scans while additional potentiostatic tests were performed for the untreated ex-situ composites. Tribo-electrochemical assays were conducted under open circuit potential (OCP) and under normal loads of 0.5 and 10 N against a 10 mm diameter alumina ball in a reciprocating ball-on-plate tribometer. Results revealed reinforcement detachments in ex-situ composites after both treatments. This was primarily attributed to oxide layer growth at the reinforcement/reaction zone interface. Hence, the use of MAO and TO on ex-situ Ti-B4C composites may not be appropriate for biomedical applications, mainly because the B4C particles tend to detach during the treatment. In contrast, TO-treated in-situ composites displayed excellent combination of corrosion and tribocorrosion performance, even under elevated applied loads, mainly due to the existence of the oxygen diffusion zone (ODZ) beneath the oxide surface produced by TO, together with the more stable electrochemical properties observed during steady-state conditions.

Formation of ceramic coatings on non-valve metal low carbon steel using micro-arc oxidation technology

Valve metals are metals that can undergo surface modification through micro-arc oxidation (MAO). Iron is not considered a valve metal and cannot undergo MAO. Steel is a widely used alloy due to its excellent properties, including high toughness, good workability, and low cost. However, its weak corrosion and abrasion resistance limit its range of application and service life. Al2O3 ceramic coating is formed on the surface of non-valve metal low carbon steel using MAO technology. The surface morphology and composition of the MAO coatings on non-valve metals are investigated through characterization. Tribological experiments show that the coefficient of friction of the samples obtained from the MAO power supply frequency of 1400 Hz is the smallest. After conducting a corrosion resistance test following MAO treatment, the impedance increased by three orders of magnitude and the corrosion rate decreased by one order of magnitude. The use of MAO treatment can expand the use of steel and shows promise for application to other non-valve metals.

Improved Corrosion Properties of Mg-Gd-Zn-Zr Alloy by Micro-Arc Oxidation

In order to improve the corrosion resistance of Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys for biomedical application, the alloy was micro-arc oxidation (MAO)-treated using silicate electrolyte system under various voltages (400 V, 425 V, 450 V, 475 V). The effects of voltage on the microstructure and corrosion properties of MAO coating were investigated via X-ray diffraction (XRD) and a scanning electron microscope (SEM) combined with an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscope (XPS), and electrochemical experiments. The results showed that, with the increase in voltage, the MAO coatings became thicker and the micropores on the MAO coating increased in diameter. The main phase compositions of the MAO coatings were MgO and Mg2SiO4. Potentiodynamic polarization curve results showed that MAO coatings could enhance corrosion resistances, where the corrosion current density decreased by six orders of magnitude and the corrosion potential of the specimens increased by 300 mV for the voltage of 450 V in the MAO treatment; nevertheless, the corrosion resistance rapidly deteriorated due to the creation of large micropores in the MAO coating, which provide a pathway for corrosive media when the voltage is 475 V. The electrochemical impedance spectroscopy results showed that MAO treatments could increase low-frequency modulus resistance and increase the corrosion resistance of Mg alloys. In addition, MAO-treated GZ31K alloys still exhibited uniform corrosion, which is desirable for biomedical applications.

STUDY ON EPOXY RESIN/MULTI-WALLED CARBON NANOTUBES CONDUCTIVE COATING ON AZ31 MAGNESIUM ALLOY AFTER MICRO-ARC OXIDATION

After micro-arc oxidation, the surface properties of AZ31 magnesium alloy have been improved. However, micro-arc oxidation treatment leads to high insulation, which limits its application in electronic devices. To increase conductivity, a conductive coating was developed by adding multi-walled carbon nanotubes (MWCNTs) to the epoxy resin. The microstructure and performance of the coating were tested by SEM, thermogravimetric analyzer, four-probe conductivity meter, high-temperature friction and wear tester, and electrochemical workstation. The results indicate that the optimal conductivity with a resistivity of 303[Formula: see text][Formula: see text]m is obtained when the MWCNT content is at 4[Formula: see text]wt%. In addition, MWCNTs are filled with a network structure of epoxy resin, which increases the density of the coating and enhances their wear and corrosion resistance.

Analysis of the current density and electrolyte composition influence on the quality of micro-arc coatings

The results of an experimental study of oxide coatings obtained using an automated system developed by the authors in the anode-cathode mode at a ratio of the anode current to the cathode current equal to 1, at low current (0.125 A or 0.25 A) with different electrolyte composition are presented. An analysis of the dependence of the quality of the obtained coatings on the molding curves, which characterize the change in the electrical voltage on the samples depending on the time of their processing was made. It has been established that with increasing current density, the process is more intense, microdischarges begin to burn earlier, and, in general, the coating quality increases. However, at too high current densities (50 A/dm2), it is undesirable to carry out micro-arc oxidation treatment due to an increase in the coating roughness. In particular, it is expedient to use the results obtained for quality control of the technological mode under production conditions: the coating has inadequate quality if the molding curve has a distorted shape. The results obtained have been tested in the implementation of the method of formation by microarc oxidation of oxide coatings with specified properties.

The effect of Nb on the formation of TiO2 anodic coating oxide on Ti–Nb alloys through MAO treatment

This study aims to promote the growth of a porous oxidized coating of TiO2 due to oxidation of the surface of the Ti–Nb alloy substrates (Nb = 5, 10, and 25 wt%) using the micro-arc oxidation (MAO) technique. Using structural (x-ray diffraction) and microstructural (optical, confocal, and scanning electron microscopy) characterization techniques, it was observed that Nb promotes the formation of the β phase in Ti alloys, reducing Vickers microhardness and elastic modulus values. Regarding the MAO coating, the results showed that the TiO2 coatings are in the form of anatase and rutile, where Nb promotes the formation of the rutile phase, increasing the hardness of the coatings. MAO coatings have high roughness values due to the formation of porous structures characteristic of MAO surfaces. Adhesion results show that MAO coatings have low adhesion with the substrate.

Synergistic Amelioration of Osseointegration and Osteoimmunomodulation with a Microarc Oxidation-Treated Three-Dimensionally Printed Ti-24Nb-4Zr-8Sn Scaffold via Surface Activity and Low Elastic Modulus.

Biomaterial scaffolds, including bone substitutes, have evolved from being primarily a biologically passive structural element to one in which material properties such as surface topography and chemistry actively direct bone regeneration by influencing stem cells and the immune microenvironment. Ti-6Al-4V(Ti6Al4V) implants, with a significantly higher elastic modulus than human bone, may lead to stress shielding, necessitating improved stability at the bone-titanium alloy implant interface. Ti-24Nb-4Zr-8Sn (Ti2448), a low elastic modulus β-type titanium alloy devoid of potentially toxic elements, was utilized in this study. We employed 3D printing technology to fabricate a porous scaffold structure to further decrease the structural stiffness of the implant to approximate that of cancellous bone. Microarc oxidation (MAO) surface modification technology is then employed to create a microporous structure and a hydrophilic oxide ceramic layer on the surface and interior of the scaffold. In vitro studies demonstrated that MAO treatment enhances the proliferation, adhesion, and osteogenesis capabilities on the scaffold surface. The chemical composition of the MAO-Ti2448 oxide layer is found to enhance the transcription and expression of osteogenic genes in bone mesenchymal stem cells (BMSCs), potentially related to the enrichment of Nb2O5 and SnO2 in the oxide layer. The MAO-Ti2448 scaffold, with its synergistic surface activity and low stiffness, significantly activates the anti-inflammatory macrophage phenotype, creating an immune microenvironment that promotes the osteogenic differentiation of BMSCs. In vivo experiments in a rabbit model demonstrated a significant improvement in the quantity and quality of the newly formed bone trabeculae within the scaffold under the contact osteogenesis pattern with a matched elastic modulus. These trabeculae exhibit robust connections to the external structure of the scaffold, accelerating the formation of an interlocking structure between the bone and implant and providing higher implantation stability. These findings suggest that the MAO-Ti2448 scaffold has significant potential as a bone defect repair material by regulating osteoimmunomodulation and osteogenesis to enhance osseointegration. This study demonstrates an optional strategy that combines the mechanism of reducing the elastic modulus with surface modification treatment, thereby extending the application scope of β-type titanium alloy.

Effect of annealing on AZ31 magnesium alloy on MAO coatings

AZ31 magnesium alloy with different annealing temperatures was subjected to micro-arc oxidation (MAO) treatment, and its corrosion behaviour was studied using immersion experiments, polarisation curves, electrochemical impedance spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectra. The alloy, when annealed at 300 °C, had the smallest grain size and the lowest electrical conductivity. Compared to other annealed alloys, the MAO coating had the smallest pore size and porosity and better corrosion resistance. The corrosion resistance of the alloy increased initially and then decreased with the increase in annealing temperature. This is mainly because the grain size first decreases and then increases, leading to a decline in electrical conductivity and then a rise, resulting in changes in the microstructure of the coating surface.

An effective micro-arc oxidation (MAO) treatment on aluminum alloy for stronger bonding joint with carbon fiber composites

The micro-arc oxidation (MAO) treatment was used in this study to modify aluminum (Al) alloys to improve bond strength with carbon fiber reinforced polymer (CFRP). Various porous surfaces of Al alloy with better hardness, roughness and wetting were created. Void defects were reduced via using resin pre-coating (RPC) technique to guide high-viscosity epoxy into the holes, CNTs fiber bridging was constructed to improve bonding interface and epoxy adhesive layer. Combined treatments of “Na2SiO3 + KOH solution” MAO, RPC and introducing CNTs on Al alloy surface yielded 21.34 MPa, up to 156.1% increment over base strength. Original de-bonding failure on Al alloy surface was altered into dominant fiber tearing failure of CFRP composites, indicating the reinforced bond strength and stronger adhesive joint. MAO was the first try and proved as a feasible treatment for bond strength improvement, which could provide an alternative to manufacture high-performance Al-CFRP composites in industrial production.

Improvement of corrosion resistance of AZ31 magnesium alloy by laser remelting/microarc oxidation/LDH composite layer

Laser remelting (LR) pretreatment, micro-arc oxidation (MAO) treatment and layer double hydroxides (LDH) sealing post-treatment are conducted on AZ31 alloy surface in sequence. The results show that the corrosion resistance of prepared LR/MAO/LDH composite layer is significantly improved. Compared with the solution-aged AZ31 alloy and LR/MAO layer, the corrosion current densities of AZ31-LR/MAO/LDH were reduced by 4 and 2 orders of magnitude, respectively, and the self-corrosion potentials were increased by 1.23 V and 0.25 V, respectively. Laser remelting pre-treatment increased the average thickness of the MAO layer by 5–10 μm. LR/MAO/LDH composite layers can effectively improve the corrosion resistance of AZ31 alloy, and have the potential for application.

Influence of element Bi and MAO treatment on the corrosion resistance of magnesium implant

Mg-Bi alloy was prepared by metallurgical method and then surface treated by micro-arc oxidation (MAO) in this work. The influence of element Bi and MAO treatment on the corrosion resistance of Mg matrix was investigated. The results showed that, element Bi can obviously improve the corrosion resistance of Mg (2–3 orders of magnitude), which may be due to that the formation of Mg3Bi2 particles can refine the grain size of the Mg matrix. After MAO treatment, the corrosion resistance was further enhanced and the MAO treated Mg-Bi showed the best corrosion resistance, however the improvement of MAO coatings is not very huge (about two times of Mg-Bi alloy). Considering the nonuniform structure, easy degradation and instability of coating materials, Mg-Bi alloy without MAO treatment has a greater potential to be used as an implant material in clinics.

Relative assessment of the microstructure, properties and bioactivity of 3D-printed and rolled Ti6Al4V with micro-arc oxidation (MAO) and hydrothermal (HT) treatment

The surface modification of 3D printed Ti6Al4V (3D-Ti64) and rolled Ti6Al4V (RO-Ti64) was carried out using optimized micro-arc oxidation (MAO) and hydrothermal (HT) treatment processes. The results showed that the 3D-Ti64 coating had a typical porous structure that was identical to the phase composition of the RO-Ti64 coating, and both exhibited super hydrophilic properties (contact angle of 0°). It was found that the 3D-Ti64 coating (1.40 × 10−7A/cm2, 39.38 MPa) had greater corrosion current density and adhesion strength compared to the RO-Ti64 coating (0.76 × 10−7A/cm2, 33.69 MPa). In addition, the HAP crystals formed by 3D-Ti64 and RO-Ti64 coatings after being cultured in SBF were not significantly different, indicating that both coatings had comparable in vitro bioactivity. However, the 3D-printed porous Ti64 coating formed a porous structure only around the edges, while the central region had a flocculent structure with unfinished electrolytic oxidation. Moreover, it was found that more HAP crystals were formed in the edge region after HT treatment. In short, the MAO and HT treatment parameters optimized on rolled Ti alloys can be inherited for continued use on 3D-printed Ti alloy solids. However, more considerations may need to be made for the 3D printing of porous Ti alloys.

Investigation on the effect and growth mechanism of two-stage MAO coating

As a more popular surface treatment method, micro-arc oxidation technology can well solve the problems of insufficient strength and poor corrosion resistance of aluminum alloy surface. In this paper, a composite coating was obtained by using a two-stage micro-arc oxidation method different from the conventional micro-arc oxidation treatment, which solved the problem of incompatibility between the two types of electrolytes and obtained a coating with superior effect. The microscopic morphology and elemental composition were characterized by using Energy Dispersive Spectrometer (EDS)/X-ray Diffraction (XRD)/Scanning Electron Microscopy (SEM). The coating thickness was tested using a coating thickness gauge, its tribological properties were tested by friction experiments, and its corrosion resistance was tested by electrochemical corrosion tests. The results show that the coating has the advantages of large thickness, dense, good anti-wear performance, small friction coefficient and excellent corrosion resistance, which enhanced the performance of MAO coating and was an important guide for further work.

Growth characteristics and wear properties of micro-arc oxidation coating on Ti-6Al-4V with different laser texture shapes

Poor wear properties severely limit the field of application and service life of titanium alloys. Three kinds of textures (dimple, groove and mesh) were prepared by laser texturing technique and compounded with micro-arc oxidation treatment to improve the tribological properties of titanium alloys in this study. The coatings' morphology, structure, and composition were characterized, and their antiwear properties were analyzed. The results show that the proportion of rutile phase in the coating increases with increasing textured area rate and that the textured edge coating has higher Si and P content, with increased thickness and densities. In terms of friction properties, the dimpled texture shows the best friction properties when textured alone, with a 28.6 % decrease in the average coefficient of friction compared to the substrate; in contrast, the meshed texture shows the best friction properties after the micro-arc oxidation treatment, with a 76.2 % decrease in the average coefficient of friction compared to the substrate. Studies have shown that laser texturing can reduce wear by retaining abrasive debris. However, laser texturing alone does not provide a significant increase in hardness at the edge location, which is more susceptible to damage during wear, leading to more severe wear. The “tip effect” encourages the growth of a micro-arc oxide layer, and the resulting hardness of the layer helps protect the texture structure from damage. The synergistic effect of the texture and the rough, hard structural features of the coating itself enhances the wear resistance of the composite coating.

Anodic MAO coating formation on Ti-25Ta alloy

This study aims to produce an anodic layer using the micro-arc oxidation (MAO) technique on the Ti-25Ta alloy by changing the threshold current value in surface treatment processes (1.0, 1.5, 2.0, and 2.5 A). The MAO treatment processes were carried out by applying a voltage of 300 V for 60 s, and the maximum current value was changed. The results showed that increasing the current limit value resulted in an increase in the amount of rutile phase in the films, as well as an increase in the coating's thickness and contact angle. Furthermore, all coatings showed good adhesion with the Ti-25Ta substrate.

Black phosphorus-incorporated novel Ti-12Mo-10Zr implant for multimodal treatment of osteosarcoma.

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 808nm 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.

Microstructure and surface performance of hydroxyapatite-modified multilayer amorphous coating on Ti-rich TiNbZrSn medium entropy alloy: A comparative study

The present study focuses on the formation of a hydroxyapatite-modified amorphous micro-arc oxidized (MAO) coating on the TiNbZrSn medium entropy alloy (TNZS MEA) through micro-arc oxidation and microwave hydrothermal treatment (MHT). The TNZS MEA primarily consists of a body-centered cubic (bcc) and hexagonal closed-packed (hcp) structure, exhibiting a low elastic modulus and high yield strength. A porous coating with an amorphous structure was obtained after MAO treatment, displaying superior corrosion resistance to MAOed Ti. After MHT, the MAOed TNZS MEA exhibited a multilayered structure consisting of three layers: an external growth layer (hydroxyapatite nanorods), an inner layer (amorphous and crystalline structures), and a substrate layer. This composite structure demonstrated enhanced superior apatite-inducing ability and corrosion resistance compared to MHTed Ti. The improvement in bioactivity and a slight decrease in corrosion resistance can be attributed to the incomplete structure of hydroxyapatite nanorods when compared to MHTed Ti. Consequently, this work successfully achieved a hydroxyapatite-modified multilayered oxidized coating with gradient performance in term of bioactivity and corrosion resistance, establishing it as a promising candidate material for hard tissue repair.