Micro-arc Oxidation Technique Research Articles

Influence of the dual-current method on the properties and growth mechanisms of micro-arc oxidation coatings

Although the micro-arc oxidation (MAO) technique can significantly enhance metal properties, the numerous variables involved in the preparation of MAO coatings lead to inconsistent properties. This study prepared MAO coatings using both single-current and dual-current methods with varied current parameters. The effects of these methods on the coating properties were investigated. Scanning electron microscopy (SEM) was used to analyze the microscopic and cross-sectional morphologies of the coatings prepared using both methods. Subsequently, the physical phase composition of the coatings was analyzed using X-ray diffraction (XRD). Finally, the coatings' tribological and corrosion resistance properties were evaluated through tribological and electrochemical tests. The results demonstrate that coatings prepared using the decreased-current method in dual-current mode exhibit outstanding abrasion and corrosion resistance. Moreover, the mechanism of action of the method is proposed, which provides a new idea and method to enhance the performance of MAO coatings in a simple and efficient way.

Tailored micro-arc oxidation coatings to match with parylene for enhanced tribological performance of Ta-12W alloys

To improve the tribological properties of tantalum-tungsten alloys, dual-layer composite coatings are designed using micro-arc oxidation (MAO) and chemical vapor deposition (CVD) techniques. By adjusting the concentrations of NaOH and NaF additives as well as the oxidation mode (constant current/voltage) of MAO process, the microstructure and properties of underlying MAO layers are tailored for better matching with the top parylene layer, aiming to develop composite coatings capable of service under heavy loads. A comprehensive study is conducted to evaluate the effect of these parameters on the growth, microstructure, bond strength, and mechanical properties of MAO coatings, along with their subsequent impact on the friction and wear behavior under various loads for composite coatings. The findings reveal that increasing the concentration of either NaOH or NaF significantly increases the coating thickness, surface porosity, crystallinity, and hardness of MAO coatings, by promoting the spark discharge activities. However, distinct interfacial growth behavior is observed due to anionic effects caused by OH− and F−. The oxidation mode plays a crucial role in determining the mechanical quality of coatings; the constant voltage mode facilitates dense coatings with high adhesion due to its self-repairing mechanism. Furthermore, wear tests confirm that the enhanced mechanical properties and open-porosity of the MAO coatings markedly improve the tribological performance of composite coatings. This improvement is attributed to the excellent load-bearing capacity provided by hard MAO layers, as well as the anchoring and storage capabilities of the textural porous surfaces. The optimized composite coating demonstrates long-lasting low friction even under heavy loads up to 80 N.

Enhanced anticorrosive, antimicrobial and biocompatible properties of AZ91D magnesium alloy by MAO-polycaprolactone-modified ZnO composite coating

Magnesium alloys are biodegradable metal implant materials that are prone to corrosion in human body fluids and are poor biocompatible as a consequence. Herein, we report the preparation of a ceramic layer on an AZ91D magnesium alloy using the micro-arc oxidation (MAO) technique, after which polycaprolactone/citric-acid-monohydrate-modified nano‑zinc oxide was composited on the ceramic layer using a sol–gel method. The MAO-polycaprolactone-modified ZnO composite coating exhibited superior corrosion resistance compared to magnesium alloy, and a higher electrochemical impedance in simulated body fluid (1.0397 × 107 vs. 8.444 × 102 Ω·cm2). Furthermore, data from immersion, antimicrobial, hemolysis, cell-viability, and-proliferation testing revealed that the composite coating is significantly more antimicrobial and biocompatible than the magnesium alloy. We conclude that such composite coatings have considerable potential for use in biomedical orthopedic-implant applications.

Influence of triangular texture composite MAO coating on the tribological properties of aluminum alloys

To compensate for the poor friction and wear performance of aluminum alloys, in this study, four triangular textures with different area occupancy rate (5.16 %, 9.17 %, 20.63 % and 28.07 %) were prepared on the surface of aluminum alloys by laser texture technology, subsequently micro-arc oxidation (MAO) coatings were prepared using MAO technique. The treated samples were characterised by X-ray diffraction, micro-morphological analysis, optical profiler and energy dispersive spectroscopy. The tribological performance under oil lubrication conditions was tested by using a pin-disc contact rotational friction wear tester. The results showed that the sharp corners at the edges of the texture caused current concentration, which resulted in more intense sparking and accelerated MAO growth, thus creating more pores and roughening the surface of the coating. In terms of tribological performance, the triangular texture with 9.17 % area occupancy rate showed the best tribological performance before MAO coating, compared with the substrate, the average friction coefficient decreased by 64.11 %; and after the MAO coating was applied, the triangular texture composite MAO coating with 9.17 % area occupancy rate still had the best tribological performance, and its average friction coefficient further decreased compared with that of the smooth MAO coating by 33.07 %. The analysis suggests that the texture can store abrasive particles to prevent the MAO coatings from being worn through, leading to coating failure, while the hard MAO coatings can resist contact stresses well enough to prevent the texture from being flattened, leading to the failure of the function of storing abrasive debris. Therefore, the integration between texture and MAO coating can greatly enhance the anti-wear properties of aluminum alloys.

Enhancing osseointegration and angiogenesis of Titanium implants through KMnO4-Modified Montmorillonite nano-clay coating

Titanium (Ti) is a widely used and favored material for dental implants, with research efforts focusing on enhancing its osseointegration capabilities. Montmorillonite (MMT), a nano-clay, has shown significant potential in drug delivery, wound healing, and other biomedical applications. Implant coatings based on MMT have demonstrated promising results; however, challenges remain in terms of surface bond strength, stability, and uniformity. Studies have indicated that manganese (Mn) can enhance cell viability, proliferation, and adhesion by activating integrin receptors. Here, a KMnO4-modified MMT (MAO-MMT-Mn) coating was developed on Ti through the micro-arc oxidation (MAO) technique. The MAO-MMT-Mn coating significantly strengthens its bond, enabling it to withstand greater loads. The incorporation of Mn, silicon (Si) and phosphorus (P) resulted in the formation of uniformly distributed lamellar MMT, facilitating the sustained release of these elements. In vitro experiments demonstrated that the MAO-MMT-Mn coating promoted osteoblast adhesion and endothelial cell migration, and led to a significant increase in the expression of osteogenic and angiogenic genes compared to uncoated Ti. Moreover, in vivo assessments using micro-CT scans and histological staining revealed improved local osseointegration and angiogenesis after 4 weeks of implantation. In conclusion, the MAO-MMT-Mn coating offers a safe, simple, and cost-effective method to enhance the surfaces of Ti implants, thereby potentially enhancing the clinical outcomes of dental implant procedures.

Effect of electrolyte pH value on microstructure and corrosion resistance of black MAO coating on 6063 aluminum alloy

Black micro-arc oxidation (MAO) coatings were obtained on the surface of 6063 aluminum alloy by using the MAO technique in silicate electrolyte with colorant NH4VO3. The work aimed to study the effect of adjusting the electrolyte pH (pH10, pH11, pH12, and pH13) on the microstructure, mechanical properties, and corrosion resistance of black MAO coatings on 6063 aluminum alloy. The experimental results showed that the electrolyte pH had an important effect on the macroscopic morphology of the MAO coatings. As the electrolyte pH value increased, the process voltage of the sample decreased, the duration of the anodic oxidation stage and the spark discharge stage were shortened, while the duration of the micro arc oxidation stage was prolonged. Reasonable adjustment of the electrolyte pH could reduce the poriness and defects of the coatings, decrease the surface roughness of the coatings, and improve the quality and wear resistance of the coatings. The corrosion resistance of the black MAO coating obtained in the electrolyte with pH12 was superior and the corrosion current density was only 3.207×10−7 A/cm2. The immersion corrosion test further demonstrated the same results of corrosion resistance.

Synergistic lubrication effect of OLC and MoDTC for reducing friction and wear of MAO ceramic coating on TC4 alloy

AbstractTC4 titanium alloy has been widely used in the automotive field due to its exceptional properties. However, inherent defects such as low hardness and poor wear resistance for TC4 alloy limited its wider application. The microarc oxidation (MAO) technique was employed in this paper to prepare MAO coatings on TC4 titanium alloy. The microstructure, phase structure, mechanical properties, and tribological performance were systematically evaluated. The results show that the coating contains a large amount of rutile TiO2 hard phase after MAO treatment, which significantly improves the mechanical properties of the substrate. The hardness of the MAO coating can reach 581 HV.05. Furthermore, the synergistic lubrication effect of onion‐like carbon (OLC) nanoparticles and organic molybdenum dithiocarbamate (MoDTC) in PAO oil was observed for MAO‐treated TC4. Particularly, when .01 wt.% OLC is used with 1 wt.% MoDTC oil, the coefficient of friction (COF) decreases to .062, and the wear rate decreases to 4.3 × 10−7 mm3/Nm. Combined Raman and X‐ray photoelectron spectroscopy (XPS) analysis indicate that OLC is deposited on coating area to form a lubricating carbon film. Additionally, OLC can promote the decomposition of MoDTC during sliding to generate a tribofilm containing MoS2.

Variations of chemical, physical, mechanical properties, and biological and antimicrobial effectiveness of Ti alloys by coating with CaP doped with different amounts of Zn via micro-arc oxidation (MAO) technique

Titanium alloys are preferred metals as implant materials due to their advantageous combination of low density and high biocompatibility. However, the augmentation of implant surfaces with calcium-based coatings becomes essential to regulate corrosion rates and enhance the osteoconductive properties of the implant material. In this study, titanium alloys, specifically Ti6Al4V, underwent a transformative process wherein they were coated with calcium phosphate (CaP) ceramics doped with zinc (Zn) via micro-arc oxidation (MAO) technique, using varying concentrations of Zn compound in the electrolyte solutions. The chemical and physical properties of the freshly prepared samples were analyzed, both initially and after culturing them with Saos-2 cells. Furthermore, the antimicrobial efficacy against E. coli was examined. The findings unveiled the remarkable efficiency of the MAO technique in forming an uniformly distributed coat on Ti6Al4V, thereby enhancing its mechanical resilience and biocompatibility, depending upon the preparation parameters employed. It was shown that Zn doped calcium coating is very efficient to regulate various parameters such as corrosion rate and mechanical strength, and an increase in Zn content exhibited a favorable impact on cell attachment and antimicrobial efficacy. Surface modification of metallic implants via MAO technique can be applied in the production of advanced implant materials.

Effect of Discharge Energy on Micro-Arc Oxidation Coating of Zirconium Alloy.

The micro-arc oxidation (MAO) technique was used to grow in situ oxidation coating on the surface of R60705 zirconium alloy in Na2SiO3, Na2EDTA, and NaOH electrolytes. The thickness, surface morphology, cross-section morphology, wear resistance, composition, and structure of the micro-arc oxidation coating were analyzed by an eddy current thickness measuring instrument, XPS, XRD, scanning electron microscopy, energy spectrometer, and wear testing machine. The corrosion resistance of the coating was characterized by a polarization curve and electrochemical impedance spectroscopy (EIS). The results show that, with the increase in frequency, the single-pulse discharge energy decreases continuously, and the coating thickness shows a decreasing trend, from the highest value of 152 μm at 400 Hz to the lowest value of 87.5 μm at 1000 Hz. The discharge pore size on the surface of the coating gradually decreases, and the wear resistance and corrosion resistance of the coating first increase and then decrease. The corrosion resistance is the best when the frequency is 400 Hz. At this time, the corrosion potential is -0.215 V, and the corrosion current density is 2.546 × 10-8 A·cm-2. The micro-arc oxidation coating of zirconium alloy is mainly composed of monoclinic zirconia (m-ZrO2) and tetragonal zirconia (t-ZrO2), in which the content of monoclinic zirconia is significantly more than that of tetragonal zirconia.

Influence of Current Duty Cycle and Voltage of Micro-Arc Oxidation on the Microstructure and Composition of Calcium Phosphate Coating

The micro-arc oxidation (MAO) technique was employed to produce calcium phosphate coatings on titanium surfaces using an electrolyte composed of hydroxyapatite and calcium carbonate in an aqueous solution of orthophosphoric acid. The coatings’ morphology and composition were regulated by adjusting electrical parameters, specifically the duty cycle and voltage. This study examined the effects of the duty cycle and voltage during the MAO process on the microstructure and composition of calcium phosphate coatings on VT1–0 titanium substrates. Scanning electron microscopy (SEM) was utilized to analyze the microstructure and thickness of the coatings, while X-ray diffraction (XRD) was employed to determine their phase composition. The findings reveal that the surface morphology of the calcium phosphate coatings transitions from a porous, sponge-like structure to flower-like formations as the duty cycle and voltage increase. A linear increase in the voltage within the applied duty cycles led to a rise in the size of the forming particles of amorphous/crystalline structures containing phases of monetite (CaPO3(OH)), monocalcium phosphate monohydrate (Ca(H2PO4)2·H2O), and calcium pyrophosphate (γ–Ca2P2O7).

Effect of Treatment with Microarc Oxidation Technology on Tribological Properties of Nonvalve Metal Low-Carbon Steel.

Steel is one of the most widely used alloys because of its excellent properties such as high toughness, good workability, and low cost. However, steel has weak wear resistance, which limits its range of applications and service life. We have used the microarc oxidation (MAO) technique to form an Al2O3 ceramic coating on the surface of nonvalve metal low-carbon steel, which is used to enhance the wear resistance of low-carbon steel. Tribological experiments have shown that the coefficient of friction is reduced by 26.9%, hardness is improved, and wear resistance is enhanced after MAO compared to the substrate. Through a series of characterizations, the wear mechanism of the MAO samples was found to be a complex friction mechanism including abrasive wear, adhesive wear, and friction oxidation. After MAO, the wear resistance of nonvalve metal low-carbon steel is improved. The use of steel can be extended and its service life can be prolonged. This innovative approach provides a viable solution for the development of low-carbon steel coatings.

Controlled anticancer 5-Fluorouracil release from functionalized 5-FU/PLGA/CaP coating on titanium implants: Characterization, in vitro drug delivery and cytotoxicity

Work presents a novel approach for creating anticancer coatings on titanium implants using 5-Fluorouracil (5-FU) loaded in calcium phosphate which is encapsulated in poly(lactic-co-glycolic acid) (PLGA/CaP) for controllable drug release. Our method involves the hybrid ultrasound-assisted micro-arc oxidation (UMAOH) technique, which make use of an ultrasound as an additional means of energy input resulting in increased pore size, drug deposition, and layer-by-layer self-assembly of PLGA. The multilayer coatings exhibit amorphous-crystalline structure with dicalcium phosphate anhydrous (DCPA) and β-tricalcium phosphate (β-TCP) phases, Ca/P ratio of 0.3, surface roughness (Ra) of 2.3–3.5 µm, and thickness between 52–60 µm. Drug release kinetics revealed a burst release for 5FU/CaP in the initial 10–20 min and sustained release over 2–4 h. 5FU/PLGA/CaP displayed a smooth, sustained release over 5 days. Biocompatibility studies showed that extracts from drug-free CaP and CaP/PLGA samples were nontoxic to HeLa, NIH-3Т3, and MCF-7 cell lines (≥ 80 % cell viability) for 0.2–24 h. In contrast, extracts from drug-loaded carriers were cytotoxic to NIH-3T3 cells (> 60 % cell death). Notably, 5-FU impregnation in the CaP coting demonstrated varying cytotoxicity, with the following cell death order: 75 % HeLa > 68 % NIH-3Т3 > 59 % MCF-7. PLGA modification reduced cytotoxicity with the following cell death order: 61 % HeLa > 52 % NIH-3Т3 > 46 % MCF-7. This work presents a promising strategy for localized, controlled drug delivery 5FU/PLGA/CaP system, with reduced cytotoxicity compared to PLGA-free 5-FU/CaP coating, advancing implant-based cancer treatment.

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

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

Enhanced hydrogen barrier performance of ZrH1.8 via yttria-zirconia composite film developed through the ECD-MAO technique

To address the inherent shortcomings of the direct micro-arc oxidation method, this study employed a combination of electroplating and micro-arc oxidation techniques. This approach successfully fabricated a hydrogen permeation barrier film on the surface of ZrH1.8, featuring a yttria-stabilized zirconia (YSZ) composite oxide. The prepared composite film layer underwent thorough evaluations, encompassing assessments of its microstructure, phase structure, adhesion strength, thickness, barrier properties, and hydrogen permeation performance. The findings indicated that the electroplated yttrium layer contributes to the stabilization of the tetragonal phase of zirconia (T-ZrO2) during the micro-arc oxidation process, thereby enhancing the discharge behavior of the film layer. By employing this treatment method, the content of T-ZrO2 in the film layer increased to 26.70%, and the film became denser with a thickness of 60.93 μm. Additionally, the adhesion strength between the film layer and the substrate significantly improved, reaching 75.95 N, with a hardness of 393.24 HV. Furthermore, the film layer exhibited an increased hydrogen release temperature of 680 °C, demonstrating excellent performance as a hydrogen permeation barrier.

Preparation of mechanically durable superhydrophobic aluminum surfaces by LST/MAO and chemical modification

In this paper, a superhydrophobic surface with mechanical durability was prepared on 6061 aluminum (Al) alloy by combining laser surface texturing (LST) and micro-arc oxidation (MAO) techniques followed by chemical immersion treatment. The effects of processing on Al alloys with different texturing spacings on the surface morphology, roughness, surface wettability, and corrosion resistance of the subsequently formed composite coatings were analyzed. The results show that a superhydrophobic surface was obtained with the water contract angle (WCA) of 158.3 ° and the roll-off angle of 9.5 ° at a texture spacing of 300 μm. This was due to the fact that the surface microroughness texturization process created by LST on the surface increased the generation of surface nanostructures, and combined with the natural nanostructure possessed by MAO, unique " double " nanostructure was formed on the surface. This surface structure increased the area of fluoride attachment, reduced the solid-liquid contact area, and decreased the adhesion of droplets to the surface, resulting in higher hydrophobicity. Electrochemical corrosion experiment showed that the corrosion current density of LM-300 was 2 orders of magnitude lower than that of the LM-0 sample, clearly demonstrating better corrosion resistance. In addition, the prepared superhydrophobic surface presented excellent mechanical durability, and in the ceramic zirconia cyclic abrasion experiment, the superhydrophobic surface was able to withstand 61 cycles of abrasion at a pressure of about 2.5 kPa.

Analysis of the ceramic coatings' recrystallization produced on the surface of the Zr-25Ta-25Ti alloy

The objective of this study is to analyze the influence of the heat treatment temperature carried out at ultra-high vacuum on surfaces formed in the Zr-25Ta-25Ti alloy by the micro-arc oxidation (MAO) technique to produce a ceramic layer with high hardness and high wear resistance. The results of structural (XRD) and microstructural characterization (SEM, optical and confocal microscopy technique) show that the surfaces are mainly composed of zirconium dioxide (ZrO2), Ti2ZrO, and calcium oxide (CaO). The heat treatments at high temperatures (500–800 °C) altered the phases of the MAO coating, forming ZrC. Confocal images showed that increasing temperature increased the roughness of the coatings (0.65 → 1.06 μm). Consequently, the topography of the coatings, wettability, microhardness (Vickers), and wear resistance (obtained by the ball cratering technique) of the materials are also modified. The wear results show that the MAO coating has a low wear rate value due to the MAO surfaces’ high hardness, efficiently protecting the substrates of the Zr-25Ta-25Ti alloy against tribological phenomena. Finally, the increase in heat treatment temperature promoted the formation of cracks in the coatings due to the difference in thermal expansion of the MAO ceramic with the Zr-25Ta-25Ti alloy substrate, causing a decrease in the hardness value and reducing wear resistance.

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.

Mutual Impact of Four Organic Calcium Salts on the Formation and Properties of Micro-Arc Oxidation Coatings on AZ31B Magnesium Alloys

Calcium phosphate (Ca–P) coatings provide an effective approach in current research and the clinical application of Mg alloys by endowing them with improved corrosion resistance, biocompatibility, and even bioactivity. Ca-containing coatings were prepared on AZ31B magnesium alloys using the micro-arc oxidation (MAO) technique and a combination of ethylenediaminetetraacetic acid calcium disodium (EDTA–Ca), calcium glycerophosphate (GP–Ca), calcium gluconate (CaGlu2), and calcium lactate (CaLac2) as the Ca source in a near-neutral solution. The respective and mutual impacts of the four calcium salts on the formation and properties of the coatings were investigated. Experimental results indicated that GP–Ca was more decisive than EDTA–Ca, CaGlu2, and CaLac2 in the formation, morphology, and, therefore, the corrosion resistance of the coatings. GP–Ca alone could not effectively incorporate Ca2+ ions into the coatings but it could combine with EDTA–Ca, CaGlu2, and CaLac2 to bring a synergistic effect in improving the Ca content of the coatings. The bifunctional structure of CaGlu2 and CaLac2, containing hydroxyl groups and carboxylic groups with anchoring effects, enabled them to enhance the Ca content of the coatings. However, due to minor differences in functional group orientation, CaGlu2 was a little more efficient than CaLac2 in increasing Ca content, while CaLac2 was a little more efficient than CaGlu2 in improving the corrosion resistance of the coatings. Finally, the total concentration of the four calcium salts, [Ca2+]T, should be controlled at a proper level; otherwise, excessively high [Ca2+]T would produce localized microbumps originating from coating ablation, eventually deteriorating the corrosion resistance of the coatings.

Preparation of cerium-containing nanoporous titanium coatings for osseointegration and their promotion of osteogenic differentiation and anti-inflammatory properties

Conventional implants face many problems, such as failure to form good osseointegration and peri-implantitis in the early stage of implantation. It has been shown that hydroxyapatite (HA) has good osteoconductive ability. Also considering the potential of cerium oxide in osteogenesis and anti-inflammation, we prepared cerium-containing nanoporous HA coatings on the surface of pure titanium using the micro-arc oxidation (MAO) technique. The surface morphology of the coating was observed by scanning electron microscopy (SEM). The mechanical strength of the coating was examined by the ultrasonic oscillator. The elemental composition of the coating was examined by energy spectrum analysis (EDS). The ion release capacity of the cerium-containing coatings was examined by inductively coupled plasma emission spectrometry (ICP-OES). The hydrophilic properties of the coatings were examined by the hydrophilic angle test. In vitro, experiments were performed using rat bone marrow mesenchymal stem cells (BMSCs) and mouse mononuclear macrophages (Raw264.7). The biosafety of the cerium-containing coating was verified by live-dead staining and CCK-8 proliferation assay. The osteogenic and anti-inflammatory ability of the cerium-containing coating was examined by immunofluorescence staining and quantitative polymerase chain reaction (q-PCR). In addition, ion experiments were used to further demonstrate the osteogenic and anti-inflammatory potential of cerium ions. Subsequent animal experiments further demonstrated the osteoinductive potential of the cerium-containing HA coating. In conclusion, our cerium (HA)-containing coatings prepared by micro-arc oxidation on titanium surfaces show excellent osteogenic and anti-inflammatory properties, which are expected to improve the functionality of clinical implants and also lay the foundation for the clinical application of cerium ions.

Effects of Graphene Oxide on Tribological Properties of Micro-Arc Oxidation Coatings on Ti-6Al-4V

This paper investigates the effect of graphene oxide (GO) particles on the friction reduction and wear resistance of coatings on a Ti-6Al-4V alloy generated using the micro-arc oxidation (MAO) technique. Different concentrations of GO were added in aluminate–phosphate electrolyte. The composition of the MAO coatings was investigated using X-ray diffraction and the energy dispersive spectrum. Measurements of the coating’s thickness, hardness, and roughness have also been conducted. Ball-on-disk friction tests under dry conditions were carried out to reveal the tribological behavior of the MAO coating. The results showed that the coating consisted of Al2TiO5 and γ-Al2O3. The addition of GO greatly reduced the friction coefficient by 25%. The coating with 5 g/L of GO particles exhibited the lowest friction coefficient (reduced from 0.47 to 0.35). Moreover, the coating thickness become thicker (from 10 to 20 μm) with an increase in GO concentration from 0 to 10 g/L. The wear mechanism was revealed via worn surface analysis. This study provides a helpful way to improve the surface wear resistance of titanium alloys.