Plasma Electrolytic Oxidation Research Articles

Engineering bioactive MWCNT-reinforced hydroxyapatite coatings on Ti29Nb5Zr alloy by plasma electrolytic oxidation method: A comprehensive approach to dental implant surface optimization

Titanium-niobium-zirconium (TiNbZr) alloys represent a promising class of newly developed titanium-based biomaterials, engineered to exhibit superior properties for biomedical applications. This study investigates the influence of hydroxylated multi-walled carbon nanotubes (MWCNTs) on the surface properties of hydroxyapatite coatings prepared by the plasma electrolytic oxidation (PEO) method for implant applications. The optimal concentration of MWCNTs in the PEO coating was determined based on the superior surface, electrochemical, and biological properties obtained. The incorporation of MWCNTs led to an enhancement in surface roughness from Ra 0.06 ± 0.02 to Ra 0.618 ± 0.03 µm, improved wettability with a decrease in contact angle from 63.03° ± 1.1–28.29° ± 0.07, and a reduction in elastic modulus from 77.20 ± 2.26 GPa to 54.50 ± 2.22 GPa. Furthermore, electrochemical corrosion resistance analysis revealed an increase in inner passivation resistance up to 2.24 × 10 ×7 Ω.cm2 with the addition of MWCNTs. Antibacterial activity analysis demonstrated that the optimal concentration of MWCNTs resulted in a 3.1-fold and 2.7-fold reduction in E. coli and S. aureus bacteria, respectively, compared to uncoated samples. Cell viability against MC3T3-E1 cells showed a 25 % higher viability with MWCNTs than uncoated substrates.

Influence of ultrasonic power modulation on the optimisation of aluminium alloy micro-arc oxidation coating properties

Conventional micro-arc oxidation (MAO) technology, due to the randomness and transient nature of arc discharge, produces coatings with numerous defects, poor abrasion resistance, and inadequate ability to effectively block the intrusion of corrosive media. In this paper, ultrasonic-assisted technology was used to study the effect of different ultrasonic power regulation on the performance optimization of MAO coating on 6061 aluminum alloy. The coating microstructure and elemental composition were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer, and its hardness, wear resistance, corrosion resistance and other properties were tested. The results show that the prepared coating has the characteristics of high hardness, good wear resistance and excellent corrosion resistance under the assistance of ultrasonic power of 50 W. This is mainly attributed to the cavitation effect, mechanical effect and thermal effect generated by the corresponding ultrasonic power, which effectively enhances the surface quality, performance and service life of the coating. This study provides valuable insights into the interaction between ultrasound power and the resulting MAO coatings, and has important implications for optimizing ultrasound-assisted processes and improving coating properties.

The impact of LSM pretreatment on the growth behavior, electrical insulation and corrosion resistance properties of PEO coating on 6061 aluminum alloy

This work reported the influence of laser surface melting (LSM) pretreatment on the growth behavior, electrical insulation and corrosion resistance of plasma electrolytic oxidation (PEO) film on 6061 aluminum alloy. It is found that the LSM pretreatment refines the surface structure of original Al metal, generating defects that store excessive energy, thereby enhancing reaction kinetics and phase transition during the PEO process. By LSM pretreatment, uniform electrical discharge and film growth can be obtained, resulting in fewer defects and lower porosity in PEO layers. Additionally, a large amount of columnar crystals comprising of SiO2 phase are observed, which transformed from the SiO32− deposited on the surface, and the LSM pretreatment significantly improves the electrical insulation, corrosion resistance, and substrate adhesion of following PEO layer. Under the same PEO treatment duration, the breakdown voltage of coating increased by 100 V, and icorr decreased from 3.26 × 10−4 to 9.13 × 10−6 A cm−2. It is expected that the combination of LSM and PEO processes can not only enhance the surface properties of Al metal, but also expand the practical application of aluminum alloy in high-power electronic devices and related fields.

Influence of titanium carbide particles on the characteristics of microarc oxidation layer on Ti6Al4V alloy

The Microarc Oxidation (MAO) layer on titanium alloy was mainly composed of TiO2, and there were some defects, such as holes and cracks, which made the performance of the MAO layer not ideal. To enhance the properties of the MAO layer, titanium carbide (TiC) particles were added to the electrolyte of a phosphate–silicate system as an additive. Consequently, the MAO layers containing the TiC phase on Ti6Al4V alloy were produced. The MAO process, composition, microstructure, and hardness of the MAO layer were comprehensively analyzed. Their frictional performance was assessed under reciprocating friction conditions without lubrication. The findings suggested that added TiC particles in the electrolyte played a significant role in creating the MAO layer, enhancing its thickness. The electrolyte without TiC particles produced an MAO layer primarily composed of TiO2 in two different mineral forms (rutile and anatase). Adding TiC particles resulted in the presence of TiC within the MAO layer, thereby facilitating the formation of a reinforced oxide layer. This addition also led to an improvement in the densification of the layer and a reduction in porosity. Notably, corrosion resistance testing indicated that incorporating 6 g l−1 TiC into the electrolyte resulted in superior performance compared with that obtained from the base electrolyte alone by achieving 1.4 times higher corrosion resistance. Moreover, a hardness value of 690 HV for the MAO layer was attained at a content level of 9 g l−1 TiC, demonstrating a significant 65% enhancement compared to the base oxide layer. This finding also demonstrated significantly enhanced friction property with a wear-volume reduction to 0.81 mm3. The findings on the relationship between the preparation of the MAO layer and its structure and properties can provide valuable guidance for designing and preparing the MAO layer.

Preparation and characterization of mesoporous HA coating with paclitaxel loaded lignin nanospheres on titanium surface

BackgroundPrimary malignant bone tumor is a disease that can lead to death. The usually applied clinical treatment strategy is surgical resection of the primary tumor. However, tumor cells are difficult to clean up, easy to make the tumor recurrence, and the bone defect caused by surgical resection also hindered the postoperative recovery. Materials and methodsHerein, in this work, mesoporous hydroxyapatite (HA) coating with petal-structure was prepared on titanium (Ti) implant surfaces by micro-arc oxidation (MAO) to accelerate the bone growth, and then paclitaxel (PTX) loaded lignin nanospheres were deposited into the HA coatings to get a sustained release for killing residual tumor cells. ResultsThe results showed that many gaps and holes of micro-scale were formed in the petal-structured HA coatings, they worked as traps for the PTX loaded nanospheres to enhance the deposited amount and immobilization stability, playing good role of drug loading platform. The encapsulation of PTX by lignin ensured a lower release rate and a higher sustaining release time when compared with the PTX without encapsulation. In addition, the HA coating with PTX loaded lignin nanospheres showed higher killing effect to tumor cells than to osteoblast. ConclusionThe mesoporous HA coating with paclitaxel loaded lignin nanospheres endowed the titanium surface with good biological property and tumor cell-killing effect, so the obtained Ti-based material had a highly hopeful application as the localized implant for therapy of primary malignant bone tumor.

Hysteresis Phenomena at Boiling in Liquid Film Flowing down the Tubes with Microarc Oxidation Coating

Hysteresis Phenomena at Boiling in Liquid Film Flowing down the Tubes with Microarc Oxidation Coating

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.

Optimization of tribological properties and corrosion resistance of MAO coatings on LY12 aluminum alloy by co-doping with graphite particles and in situ formation of zinc phosphate

Micro-arc oxidation (MAO) coatings can enhance the wear and corrosion resistance of aluminum alloys, but the high coefficient of friction and surface pores can lead to failure in the field. In this study, zinc acetate and graphite particles are introduced to the electrolyte to form corrosion-resistant and lubricating MAO coatings on the LY12 aluminum alloy. Zinc phosphate nanocrystals formed in situ are uniformly distributed in the amorphous coating, while the extrinsic graphite is mainly located in the amorphous structure. Compared to the aluminum alloy substrate, the friction coefficient of the optimal MAO coating decreases to ∼0.2, and the wear rate decreases by nearly 10 times. Zinc phosphate nanocrystals generated in situ in the coatings release Zn2+ during corrosion attack to cover the vulnerable weak corrosion areas around the pores. The corrosion resistance is improved significantly, as manifested by the increase of the corrosion potential from −1.290 V to −0.811 V and the decrease of the corrosion current density from 3.172 × 10−6 A cm−2 to 4.320 × 10−10 A cm−2. The co-doped MAO coatings have better wear and corrosion resistance and are more suitable than the LY12 alloy in many engineering applications.

Long-term superhydrophobic, antibacterial, and corrosion-resistant Ag-loaded LiAl-LDH composite coating grown in-situ on MAO coating

This study successfully prepared long-term superhydrophobic, antibacterial, and corrosion-resistant lithium aluminum layered double hydroxide (LiAl-LDH) modified with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) through a hydrothermal reaction. The LiAl-LDH was in situ grown on the micro-arc oxidation (MAO) film and loaded with Ag nanoparticles. The results showed that at a hydrothermal reaction temperature of 150 °C, LiAl-LDH effectively filled the microscopic defects of the MAO coating, significantly enhancing its hydrophobicity. After PFOTES treatment, the water contact angle remained above 150° even after 75 days of immersion in simulated seawater. Additionally, the introduction of Ag+ notably improved the antibacterial properties of the coating. Electrochemical tests indicated that the corrosion resistance of the coating increased with higher hydrothermal temperatures. The corrosion current density of the coating obtained at 150 °C was measured at 2.30 × 10−9 A∙cm−2, which is two orders of magnitude lower than that obtained at 100 °C. Following hydrophobic modification, the corrosion current density decreased further, and after 50 days of immersion in simulated seawater, the |Z|0.01Hz value remained above 108 Ω·cm2, demonstrating excellent corrosion resistance. This study provides important experimental and theoretical foundations for developing metal surface protective coatings with broad application prospects.

Enhancing corrosion resistance of plasma electrolytic oxidation coatings on AM50 Mg alloy by inhibitor containing Ba(NO3)2 solutions

Enhancing corrosion resistance of plasma electrolytic oxidation coatings on AM50 Mg alloy by inhibitor containing Ba(NO3)2 solutions

A novel high corrosion-resistant and superhydrophobic MAO-30/PA/VTES composite coating on Cu[sbnd]15Fe alloy for long-term corrosion protection

The copper (Cu) alloys are prone to severe corrosion in marine environments. In this work, we successfully develop a novel high corrosion-resistant and superhydrophobic MAO-30/PA/VTES composite coating on Cu15Fe alloy for long-term corrosion protection. The composite coating, with a corrosion rate of 0.00001 mm/y and a water contact angle of 152.7°, presents significant advantages over most Cu alloys modification methods to date. Benefiting from the modification with phytic acid (PA) and vinyltriethoxysilane (VTES), the corrosion current density of the composite coating remains 2.14 × 10−10 A·cm−2 even after 168 h of immersion in 0.6 M NaCl, which is four orders of magnitude lower than Cu15Fe substrate (5.68 × 10−6 A·cm−2). The exceptional long-term corrosion resistance of the composite coating is attributed to the physical barrier effect of the micro-arc oxidation (MAO) layer, the superhydrophobic characteristics and sealing effect of the PA/VTES film layer, and the chelating effect of the phytic acid. Developing the composite coating introduces a new approach to protecting Cu alloys from corrosion in marine environments.

Effect of SiO2-reinforcement and alkali treatment on the corrosion resistance of plasma electrolytic oxide coating on AZ31 magnesium alloy

Plasma electrolytic oxidation (PEO) produces an oxide coating containing pores and cracks lowering corrosion protection. The defects can be sealed by in-situ or post-treatment methods. This work compares the sealing effect of SiO2 particles and post-alkali treatment on the corrosion resistance of PEO coatings formed on AZ31 magnesium (Mg) alloy. PEO was conducted in a phosphate-based electrolyte containing 2 g/l nanoparticle SiO2 at a constant current density of 300 A/m2 for 10 min. The post-alkali treatment was performed in 0.5 M NaOH solution at 80 °C for 30 min. The corrosion resistance was evaluated using polarization, electrochemical impedance spectroscopy, and weight loss tests. The SiO2 particles were successfully embedded uniformly in the Mg3(PO4)2 coating, enhancing the coating compactness and stability. The reinforced coating exhibited ten times higher impedance modulus and lower corrosion current density. The post-alkali treatment improved corrosion resistance but not as high as the SiO2 reinforcement. The impedance modulus of the alkali-treated specimen increased five times, and the corrosion current density decreased three times of the base coating. The weight loss test consistently showed that the SiO2-reinforced coating generated lower mass loss during 14 days of immersion in simulated body fluid.

Simple incorporation and calcination of Zn-Al LDH during PEO processing in near-neutral pH solutions

Plasma electrolytic oxidation (PEO) process was employed for preparing oxide coatings on AA2024 aluminum alloy in solutions containing Zn-Al layered double hydroxide (LDH) particles. Sodium hexametaphosphate aqueous solution was selected as the standard solution, based on its almost neutral pH value considered as important for the LDH stability. Different additives to the standard solution were examined including 2-mecaptobenzothiazole (MBT) and different Zn-Al LDH compounds. The formed coatings underwent characterization regarding their morphology, chemical and phase composition, as well as assessment of their photocatalytic and corrosion protection efficiency. Coating thickening and compactness evolution were noted for all coatings with LDH additions to the standard solution. Obtained coatings are well-crystallized featuring γ-Al2O3 and two Zn-containing crystalline phases, namely ZnO and NaZnPO4, originating mainly from the LDH addition to the solution. PEO coatings obtained in this study demonstrated very reasonable photocatalytic activity for immobilized photocatalyst, reaching 51 % after 6 h under UV irradiation. The inclusion of Zn-Al LDH substantially boosted the impedance modules at low frequencies by two orders of magnitude compared to bare AA2024 alloy when exposed to a 3.5 % NaCl solution.

Correlative study of Mott–Schottky analysis and corrosion behaviour of plasma electrolytic oxidation treated magnesium alloy: Effect of Cl⎺ concentrations

Semiconducting and corrosion properties of the plasma electrolytic oxidation treated AM50 magnesium alloy was correlatively investigated as a function of Cl⎺ content. Semiconducting character transitioned from p – type (for 0.01 M Cl⎺) to n – type (for both 0.1 and 1 M Cl⎺). Corrosion potential moved progressively to noble potential with the increase in Cl⎺ content. Variations of impedance modulus at lowest frequency employed (|Z|0.1 Hz), resistance of inner barrier layer (RIL), and corrosion current density with the Cl⎺ content were correlated with the variations of the defect density, change in Ecorr – Efb. and thickness of space charge layer.

Duplex plasma electrolytic oxidation/ hydroxyapatite- polydopamine coating on WE43 alloy for bone implants: Long-term corrosion resistance and biological properties

This study aims to evaluate the corrosion behavior of WE43 alloy with plasma electrolytic oxidation (PEO)/hydroxyapatite (HA)-polydopamine (PDA) duplex coating. HA-PDA is co-deposited as the top layer using an electrodeposition process by varied dopamine hydrochloride concentration and deposition time following the PEO process. The findings show the development of a corrosion-resistant coating by regulating the surface morphology. Furthermore, long-term electrochemical impedance spectroscopy reveals that the total impedance of the optimized PEO/HA-PDA coating (deposition time = 10 min and dopamine hydrochloride concentration = 1 mg/mL) increased from 1720 Ω on day 1 to 14,600 Ω following 21 days of immersion. Co-deposited HA-PDA shows less hydrogen release and higher adhesion strength than PEO/HA samples. Finally, the PEO/HA-PDA coating is desirable for magnesium bone implants by considering the bioactivity of the coating resulting in improved cell-surface interaction.

In-situ incorporation of polydopamine surface modified bioactive glass nanoparticles into a plasma electrolytic oxidation coating on biodegradable AZ31 Mg alloy: A study of bioactivity and corrosion performance

Magnesium alloys are promising candidates for next-generation biodegradable biomaterials. However, their poor corrosion resistance has limited their medical applications. In this study, to improve the bioactivity performance and control the degradation rate of an AZ31 Mg alloy, anodic oxide coatings containing bioactive glass (BG) were created on the alloy using plasma electrolytic oxidation (PEO). First, BG nanoparticles were synthesized through the sol-gel method and surface-modified with polydopamine (BG/PDA). These nanoparticles were then dispersed in an alkaline phosphate electrolyte and incorporated into the coatings grown using unipolar and bipolar waveforms. According to EDS results, incorporation of BG/PDA nanoparticles was higher when the bipolar waveform was applied. Electrochemical impedance spectroscopy revealed that the coatings significantly enhanced the corrosion resistance of the AZ31 Mg alloy, with the BG/PDA nanoparticle-containing coatings demonstrating the lowest degradation rate during long-term immersion. These coatings achieved the highest faradic resistance of ∼ 12 kΩ.cm² after 28 days of immersion. The incorporation of BG and BG/PDA nanoparticles enhanced the bioactivity performance of the coatings, facilitating hydroxyapatite formation on the coating surface. Based on the results, the newly developed BG-coated alloy shows promising potential for biomedical applications.

Growth mechanism and performance of MAO-AO composite coating obtained by two-stage process

Titanium alloys, with the high specific strength and low elastic modulus, are currently the research focus of many applications. Various surface treatments have been applied with the intention of improving their wear and corrosion resistance. Micro-arc oxidation (MAO) technology originated from anodic oxidation (AO) technology, which has the advantages of simple process, high efficiency and environmentally friendly electrolyte. However, due to the micro-arc discharge effect, MAO coatings inevitably show the characteristic of high porosity. In this study, post-treatment of MAO coatings using AO was proposed to obtain a composite coating with both high hardness and low roughness and porosity thereby compensating for the defects of MAO coatings. After preparation, each sample was analyzed and characterized. The results indicated that AO was main conducted in the discharge channel of MAO coating and an amorphous phase coating with the matrix oxide as main component was grown in situ. The composite coating showed a slight increase in thickness and significant reduction in roughness than MAO coating and with superior wear and corrosion resistance. In conclusion, this study provides new idea and data support for improving the performance of MAO coatings, which is expected to be widely used in the field of surface treatment.

Exploring the impact of iron doping on the photocatalytic efficiency of TiO2 coatings produced on Ti via PEO

In this study, composite coatings of TiO2/Fe3+ were developed by incorporating Fe(NO3)3 into TiO2-based coatings, produced via plasma electrolytic oxidation (PEO) on unalloyed titanium. The ability of these coatings to photodegrade methylene blue (MB) under visible light was investigated. The morphology, chemical composition, and optical properties of the PEO coatings were characterized using various techniques, including X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and UV–Vis diffuse reflectance. All coatings exhibited a porous structure, with phase analysis revealing the formation of anatase and rutile phases during the coating process. The coatings were also found to be hydrophobic. Increasing the concentration of Fe(NO3)3 in the composite coatings from 0 to 0.1 g/L resulted in a decrease in the optical band gap energy from 3.05 eV to 2.95 eV. The PEO coating with 0.10 g/L of Fe(NO3)3showed the highest photocatalytic activity (PA), achieving 70 %. This improvement in PA is likely due to the formation of a heterojunction, which effectively separates electron/hole pairs.

Bridge for the thermodynamics and kinetics of electrochemical corrosion: The design of self-densified plasma electrolytic oxidation coating on Mg alloys

A new perspective was reported to design the self-densified plasma electrolytic oxidation (SDF-PEO) coatings on magnesium alloys based on the dissolution-ionization-diffusion-deposition (DIDD) model. The main considerations of the new PEO electrolyte include the establishment of a thermodynamics diagram, the construction of a liquid-solid sintering system and the regulation of plasma sparkling kinetics. The SDF-PEO coating exhibited a homogeneous and dense microstructure, superior corrosion resistance and good technological adaptability. This work offers a novel theory to design surface treatment solutions with superior corrosion resistance and promising application prospects.

Enhancement of PEO-coated ZK60 Mg alloy: Curcumin-enriched mesoporous silica and PLA/bioglass for antibacterial properties, bioactivity and biocorrosion resistance

The corrosion resistance and antibacterial properties of ZK60 magnesium alloy implants have been enhanced via Plasma Electrolytic Oxidation (PEO) and electrospinning techniques. A robust, porous oxide coating was created on the ZK60 alloy using the PEO process, with characterization performed via SEM and XRD. Improved corrosion resistance of the PEO-coated samples was demonstrated through electrochemical analyses, including EIS and polarization tests. In addition to the PEO treatment, composite electrospun nanofibrous coatings were developed, incorporating curcumin-loaded mesoporous silica nanoparticles and bioactive glass. The electrospun nanofibers, which exhibited a diameter of 350 nm without beads, were characterized by Dynamic Light Scattering, Zeta Potential, Infrared Spectroscopy, BET, and XRD, confirming a curcumin loading of 10 wt%. Significant antibacterial activity against Escherichia coli and Staphylococcus aureus was shown by these fibers, and high bioactivity was observed after 14 days of immersion in simulated body fluid (SBF). The combination of PEO coatings and electrospun nanofibers highlights an enhancement in both corrosion resistance and antibacterial properties for implant applications.