Micro-arc Oxidation Technique Research Articles

The hydrothermal performance and corrosion resistance of MgO@Nb2O5 composite coatings on Mg–7Y alloy in natural seawater

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

Preparation, interface properties and corrosion behavior of nano-modified MAO ceramic film on 5B70 Al alloy

Ceramic film with graphite oxide (GO) particles were prepared on 5B70 Al alloy by micro-arc oxidation（MAO）technique. Effect of GO concentrations on the micro-arc oxidation behavior, ceramic/metal interfacial characteristic and the anti-corrosion performance of MAO ceramic films was studied. The experimental results indicated that the GO additive could decrease the breakdown voltage, enhance the MAO reaction, decrease the surface roughness, reduce the porosity, increase the film thickness, and improve the ceramic/metal interface adhesion. The MAO ceramic film prepared in the electrolyte with 0.15 g/L GO additive had the best corrosion resistance in 3.5 wt% NaCl solution, as manifested by a corrosion current density of 3.72 × 10−8A·cm−2 that was 2 orders of magnitude less than that of the 5B70 Al alloy substrate. The same results of corrosion resistance were also verified by immersion corrosion test.

Study on microstructure of rare earth Mg-9%Gd-2%Y-3%Nd -0.7%Zr alloy and properties of micro-arc oxidation films

The micro-arc oxidation protective film has been prepared on the surface of Mg-9%Gd -2%Y-3%Nd-0.7%Zr alloy by using the microarc oxidation technique of “step by step depressurization”. The microstructure of magnesium alloy substrate and micro-arc oxidation film were measured by OM, SEM and XRD, and the properties of the film were evaluated by electrochemical test of film thickness and surface morphology. The results show that the discontinuous network multiple eutectic phases are distributed in the grain boundary and there are dispersed-granular precipitates in the alloy matrix. After the micro-arc oxidation treatment, the thickness and corrosion resistance of the micro-arc oxidation film increased with the increase of oxidation time, and the surface micropore size increased first and then decreased, and the surface morphology of the micro-arc oxidation film changed from no micro-crack to micro-crack, and finally the micro-crack disappeared.

Processing and Analysis of Micro-Arc Oxidation Coating on 319S Aluminum Alloy

In this study, a high-hardness and wear-resistant ceramic coating was prepared on the surface of 319S aluminum alloy using the micro-arc oxidation (MAO) technique. The effects of pulse width, negative voltage, and KOH concentration on the MAO coating were investigated, and the microhardness and surface roughness of the coating were measured. The morphology, elemental distribution, and phase composition of the coating were analyzed using SEM, EDS, XRD, and digital microscopy. The influence of the MAO coating on the wear of the 319S aluminum alloy was evaluated using a friction-wear tester. The results showed that in the sodium silicate solution system, with an increase in pulse width, the thickness of the coating gradually increased and the surface hardness initially increased and then decreased. With an increase in negative voltage, the density of the coating first increased and then decreased, the thickness of the dense layer initially increased and then decreased, and the surface hardness initially increased and then decreased. With an increase in the KOH concentration, the coating thickness increased and the roughness initially decreased and then increased. When the pulse width was 3000 ms, the negative voltage was 130 V, and the KOH concentration was 1 g/L, the coating exhibited the best density, with the highest surface hardness of 1426.8 HV and the thickest dense layer of 55 μm. The reduction in surface cracks and improvement in density indicated an enhancement in the hardness and wear resistance of the coating. The decrease in width and depth of the wear scars demonstrated the excellent wear resistance of the coating.

Study on Growth Mechanism and Characteristics of Zirconium Alloy Micro-Arc Oxidation Film

Ceramic coatings on R60705 zirconium alloy were prepared on the surface by the micro-arc oxidation (MAO) technique in electrolytes containing Na2SiO3, NaOH, and Na2EDTA. The growth behavior of the MAO ceramic coatings at different stages, including growth rate, microstructure, and phase composition, was investigated using the method of direct observation of the boundary area. The results showed that the growth of the MAO coatings on R60705 zirconium alloy occurred in both inward and outward directions. At an oxidation time of 5 min, the thickness of the oxidation layer increased fastest, reaching 103.43 μm, with a growth rate of 0.345 μm/s. After 5 min, the growth rate decreased and tended to level off around 15 min, with a thickness and growth rate of 162.7 μm and 0.181 μm/s, respectively. The total thickness of the coatings continuously increased throughout the process, with the outward growth thickness always higher than the inward growth thickness. The composition of the zirconium alloy micro-arc oxidation coatings mainly consisted of monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2), and a small amount of SiO2. The main elements in the coatings were Zr, O, and Si. The corrosion resistance of the zirconium alloy micro-arc oxidation coatings increased first and then decreased with increasing oxidation time, with a corrosion current density of 8.876 × 10−9 A·cm−2 at 15 min, indicating the best corrosion resistance.

Micro-Arc Oxidation Enhances Mechanical Properties and Corrosion Resistance Of Ti-6Al-7Nb Alloy

Investigation results of micro-arc coating on the (Ti-7Nb-6Al) alloy were presented. It has potential clinical value in applications such as dental implant, knee, and hip prostheses. An electrolyte solution of ( Na2CO3 + Na2SiO3). The micro-arc oxidation (MAO) technique was employed for in situ oxidation of Ti-6Al-7Nb surface. The wettability of a porous TiO2 covering made up of anatase and rutile phases was investigated. The test findings revealed that the possibility of deposition of ceramics coatings on the surface of Ti-6Al-7Nb alloy by using voltages (400V )at different deposition times (7, 15, and 30) min. The results indicate that ceramics layer of titanium oxide (TiO2) which is formed during coating porous and homogenous distribution. The bioactive composition of the oxide layers can be suitable for use as advanced biomedical implants. The coatings also revealed an increased surface roughness, porosity, microhardness, surface wettability and corrosion resistance of the Ti-6Al-7Nb substrate reaches to (CR= 0.1114×10−3mpy) in Ringer’s solution and (CR= 1.03×10−3mpy) in Saliva’s solution with increased deposition time.

Incorporation of Al2O3 and ZrO2 ceramics to AZ31 magnesium alloys composite coating using micro-arc oxidation method

In this research, a composite coating with Al2O3 and ZrO2 particles have been applied on AZ31 magnesium alloy by micro-arc oxidation (MAO) technique. The alkaline electrolyte included a constant based composition and different composition of the Al2O3 and ZrO2 additives. Microstructure observations reveal that the surface pores of composite coating reduced during addition of ZrO2 and Al2O3 ceramic particles. The hardness of coating increased from about 380 for non-added to 620 MPa for Al2O3+ZrO2 added coating and wear rate reduced about 8 times. Wettability of the coating increased by incorporation of Al2O3 and/or ZrO2 particles while, Al2O3 is more effective than ZrO2. Addition of the ceramic particles enhanced the hydrophilicity properties of surface in wettability test and a contact angle of 43° was obtained for coating including Al2O3+ZrO2. The antibacterial properties of MAO coatings showed that S. aureus bacterium is more sensitive to the zirconia and alumina particle than S. typhimurium bacterium after 24 h of incubation.

Effect of current density on tribological properties of micro-arc oxidation ceramic film on Al-Mg-Sc alloy

Ceramic films on Al-Mg-Sc alloy were prepared in alkaline sodium silicate electrolyte solution at different current densities by micro-arc oxidation (MAO) technique. The influence of current density on the microstructure and tribological property of the MAO ceramic films was investigated. The experimental results indicated that the surface porosity decreased and roughness increased with the increase of current density. The optimal anti-friction effect of the MAO ceramic film prepared at the current density of 10 A dm−2 was obtained. The wear mechanism of MAO ceramic film was the coexistence of abrasive wear, adhesive wear and oxidation wear. The wear resistance of MAO ceramic film prepared on Al-Mg-Sc alloy structural components could be increased, which could reduce the risk of failure of structural components due to mechanical vibration.

A functional study of zinc-titanium coatings and exploration of the intrinsic correlation between angiogenesis and osteogenesis.

With the development of implant applications, osseointegration has become a criterion for implant success. A good blood supply is essential for successful osseointegration. To improve the pro-angiogenic ability of the implants, in this experiment we introduced zinc into the titanium coating. The physical morphology, biocompatibility, pro-angiogenic ability, and osteogenic effect of the zinc-containing titanium coatings were investigated. The pro-angiogenic effect of zinc ions was determined, and the intrinsic link between angiogenesis and osteogenesis under the effect of zinc ions was investigated. Zinc-containing titanium coating was prepared using a micro-arc oxidation (MAO) technique. The physical properties of the coating materials were determined by analyzing the microstructure, roughness, hydrophilic properties, constituent elements, and ionic release of the coating. The biocompatibility of the coating materials was examined using apoptosis and proliferation assays of human umbilical vein endothelial cells (HUVECs). The pro-angiogenic function and osteogenic ability of the zinc-containing coating were investigated by CD31 immunofluorescence staining and quantitative polymerase chain reaction (q-PCR) assay. The optimal concentration of zinc ions for pro-angiogenesis was screened by ion assay. Conditioned media (CM) were prepared for the experiments. The intrinsic link between angiogenesis and osteogenesis was determined by q-PCR to detect the expression of genes related to HUVECs and BMSCs after culture in CM. The prepared Zn-containing micro-arc oxide coatings were shown to have good physical properties, stable Zn2+ release ability, and biocompatibility, as well as good angiogenic and osteogenic potential. In addition, ion experiments confirmed that 60 μM Zn2+ exhibited the best angiogenic effect; more importantly, a mutual promotion between angiogenesis and osteogenesis regeneration in the Zn2+ microenvironment was also found. The introduction of Zn2+ improved the implants' functionality and laid the foundation for the clinical application of Zn2+ pro-angiogenesis.

Osteogenic and long-term antibacterial properties of Sr/Ag-containing TiO2 microporous coating in vitro and in vivo.

Bacterial infection and poor osseointegration are two critical issues that need to be solved for long-term use of titanium implants. As such, Sr/Ag-containing TiO2 microporous coatings were prepared on a Ti alloy surface in the current study via a single-step microarc oxidation technique. The coatings showed both good cytocompatibility in vitro and biosafety in vivo. Sr/Ag incorporation brought no significant change in the surface micromorphology and physicochemical properties, but endowed the coating with strong osteogenic activity and long-term antibacterial capability in vitro. Furthermore, the osteogenic and antibacterial capability of the coating was also confirmed in vivo. In a rat osseointegration model, new bone formation, implant-bone contact, removal torque and bone mineralization were all significantly increased in the M-Sr/Ag group when compared with those in group M, although they were slightly lower than those in group M-Sr. In a periimplantitis model, no rats suffered infection in the M-Sr/Ag group after 3 months of osseointegration and 5 weeks of bacterial inoculation period, when compared to 100% and 75% infection rates in M and M-Sr groups, respectively. In addition, active bone remodeling and many mesenchymal cells were observed in the M-Sr group, suggesting good bone regeneration potential in Sr-containing coatings in the case of controlled periimplantitis. Overall, the Sr/Ag-containing TiO2 microporous coating is valuable for preventing periimplantitis and improving implant reosseointegration, and is therefore promising for long-term and high quality use of titanium implants.

A novel TiO2-SnO2 film pH sensor prepared by micro-arc oxidation

In this work, we have used a micro-arc oxidation technique operating in the AC mode to prepare a TiO2-SnO2 film sensitive to pH on a Ti substrate. The microstructure and elemental and material composition of the film was studied. The results show that a porous structure formed on the film surface. XRD indicated that the film contained hydrophilic amorphous TiO2, and XPS showed the formation of oxide SnO2 in the film. TiO2-SnO2/0.5 films doped with 0.5 g/L Na2SnO3 had excellent pH-sensing properties. Performance tests showed that for pH in the range 2–12, the TiO2-SnO2/0.5 films had a sensitivity of 64.60 mV/pH, as well as fast response times, low hysteresis, good stability, and resistance to temperature and interference by ionic impurities. The prepared TiO2-SnO2/0.5 films were used with a commercial pH meter to detect several common fluids with an accuracy of ± 0.09 pH.

The effect of strontium content on physicochemical and osteogenic property of Sr/Ag-containing TiO2 microporous coatings.

Strontium (Sr) is the most common element introduced into TiO2 coatings to strengthen the osteogenic property of titanium implants. However, the optimal Sr content and its effect on osteogenic and physicochemical properties of the coatings need to be clarified. In the current study, TiO2 microporous coatings with different contents of Sr (9.64-21.25 wt %) and silver (Ag) (0.38-0.75 wt %) were prepared via micro-arc oxidation technique. Sr contents did not change physicochemical properties of the coatings, including surface microstructure, micropore size and distribution, phase composition, roughness and hydrophilicity. Meanwhile, higher Sr contents (18.23-21.25 wt %) improved cytocompatibility, proliferation and alkaline phosphatase (ALP) activity of preosteoblasts, even the coatings underwent 30 days' PBS immersion. Furthermore, higher Sr contents facilitated preosteoblast growth and spreading, which are essential for their proliferation and osteogenic differentiation. Therefore, it is promising to incorporate higher Sr content (18.23-21.25 wt %) within TiO2 microporous coatings to improve their osteogenic capability.

Research on wear and high cycle fatigue performance of ceramic coatings produced on Ti-6Al-4V alloy by micro-arc oxidation

Ceramic coatings were produced on the surface of Ti-6Al-4V titanium alloy by Micro-Arc Oxidation (MAO) technique. The morphology and phases of coatings were investigated by scanning electron microscopy (SEM), and X-ray diffraction (XRD) technologies. The friction and high cycle fatigue properties were tested in coated and uncoated specimens. The results show that the MAO coatings were mainly composed of the anatase TiO2 phase, which grows in-suit on the surface of the substrate material. There was no transition layer between the coatings and the substrate, and a high bonding strength was obtained. The anti-abrasion properties of the coated specimens were improved because of the high hardness of ceramic coatings. MAO generates many micro-pores. During fatigue loading, the micropores act as notches to cause stress concentration, which can decrease the fatigue life of substrate material.

Final surface modification for better wear resistance of ceramic coating on cast AlSi10Mg alloy

Using the design of experiment (DOE) method and the micro-arc oxidation (MAO) technique, ceramic layers on AlSi10Mg alloy were systematically prepared to design optimal process conditions for achieving the best tribological properties of the ceramic layers. The lowest concentrations of the applied 6 g/l NaOH and 12 g/l Na 2 SiO 3 resulted in the preparation of uniform MAO layers with the lowest rated parameters R a , R z and thickness achieved under micro-arc discharge conditions at 500 V and 60 min. With the increasing thickness of the coatings, there was an increase of Si in the MAO coating. Full factorial DOE was used to optimize the tribological properties in a polyalphaolefin (PAO) environment at 80 °C. The most significant influence for the preparation of abrasion-resistant layers for the investigated factors was identified on the AlSi10Mg alloy by the NaOH content in the electrolyte. The friction coefficients of MAO coatings reached an average value of 0.15. Aero-lap polishing technology was applied for increased wear resistance requirements to eliminate the deficiencies of MAO coatings, leading to decrease wear track by almost double compared to polished silumin. Removal of the outer MAO layer by polishing led to a reduction in the high corrosion resistance of the MAO coating, demonstrating the influence of the outer layer not only on the tribological properties but also on the corrosion resistance of MAO coatings.

AMPK/mTOR Pathway Is Involved in Autophagy Induced by Magnesium-Incorporated TiO2 Surface to Promote BMSC Osteogenic Differentiation.

Magnesium has been extensively utilized to modify titanium implant surfaces based on its important function in promoting osteogenic differentiation. Autophagy has been proven to play a vital role in bone metabolism. Whether there is an association between autophagy and magnesium in promoting osteogenic differentiation remains unclear. In the present study, we focused on investigating the role of magnesium ions in early osteogenic activity and the underlying mechanism related to autophagy. Different concentrations of magnesium were embedded in micro-structured titanium surface layers using the micro-arc oxidation (MAO) technique. The incorporation of magnesium benefited cell adhesion, spreading, and viability; attenuated intracellular ATP concentrations and p-mTOR levels; and upregulated p-AMPK levels. This indicates the vital role of the ATP-related AMPK/mTOR signaling pathway in the autophagy process associated with osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) induced by magnesium modification on titanium surfaces. The enhanced osteogenic differentiation and improved cellular autophagy activity of BMSCs in their extraction medium further confirmed the function of magnesium ions. The results of the present study advance our understanding of the mechanism by which magnesium regulates BMSC osteogenic differentiation through autophagy regulation. Moreover, endowing implants with the ability to activate autophagy may be a promising strategy for enhancing osseointegration in the translational medicine field in the future.

Improvement of steam oxidation resistance of the γ-TiAl alloy with microarc oxidation coatings at 900–1200 ℃

A dense ceramic coating of ∼30 µm on the γ-TiAl alloy was fabricated using the microarc oxidation (MAO) technique. The coated alloy was oxidized under 900–1200 ℃ steam environments for 3600 s. The oxidation rate for the MAO-coated TiAl alloy is significantly lower than the pristine TiAl alloy. The MAO coating remains intact through the oxidation tests, while the layered structures are formed beneath the MAO coating, which are characterized in detail with X-ray diffraction, scanning and transmission electron microscopy. The improvement of steam oxidation resistance is attributed to the barrier effect of the MAO coating.

Multidynamic Osteogenic Differentiation by Effective Polydopamine Micro-Arc Oxide Manipulations.

IntroductionThe nanostructural modification of the oral implant surface can effectively mimic the morphology of natural bone tissue, allowing osteoblasts to achieve both proliferation and differentiation capabilities at the bone interface of the dental implant. To improve the osteoinductive activity on the surface of titanium implants for rapid osseointegration, we prepared a novel composite coating (MAO-PDA-NC) by micro-arc oxidation technique and immersion method and evaluated the proliferation, adhesion, and osteogenic differentiation of osteoblasts on this coating.MethodsThe coatings were prepared by micro-arc oxidation (MAO) technique and immersion method, and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for different coatings; the loading of PDA was examined using Fourier transform infrared spectroscopy (FTIR); the ion release capacity of the coatings was determined by inductively coupled plasma emission spectrometry (ICP-OES); the interfacial bonding of the coatings was examined using nanoscratch experiment strength. The cytotoxicity of the coating was examined by live/dead staining kit; cell proliferation viability was examined by CCK-8 kit; adhesion and osteogenic effect of the coating were examined by immunofluorescence staining and RT-PCR; osteogenic differentiation was examined by alkaline phosphatase staining.ResultsThe surface morphology of titanium implants was modified by micro-arc oxidation technology, and a new MAO-PDA-NC composite coating was successfully prepared. The results showed that the MAO-PDA-NC coating not only optimized the physical and chemical properties of the titanium implant surface but also significantly stimulated the biological properties of osteoblast adhesion, proliferation, and osteogenic differentiation on the coating surface.ConclusionThese results show that MAO-PDA-NC composite coating can significantly improve the surface properties of titanium implants and achieve a stable bond between implant and bone tissue, thus accelerating early osseointegration.

Investigation of anti-corrosion property of hybrid coatings fabricated by combining PEC with MAO on pure magnesium

• Novel hybrid coatings are prepared by combining PEC with MAO on pure magnesium. • PEC modified layers play a positive effect on improving corrosion resistance of PEC+MAO hybrid coatings. • PEC+MAO hybrid coatings can further enhance corrosion resistance of pure magnesium. Novel hybrid coatings on pure magnesium were prepared by combining plasma electrolytic carburizing (PEC) with micro-arc oxidation (MAO) to further enhance the anti-corrosion property in this paper. Scanning electron microscopy (SEM) was used to observe the micro-structure of the coatings, meanwhile, energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were separately used to investigate the elemental as well as phase compositions of the coatings. The anti-corrosion property of the coatings was evaluated by potentiodynamic polarization curves as well as electrochemical impedance spectroscopy (EIS).The results show that PEC process is closely related with the effects of adsorption as well as diffusion of the activated carbon atoms, and it can provide a favorable pretreatment surface with predesigned chemical composition to obtain a new kind of phase, namely SiC with superior corrosion resistance and chemical stability, in the following PEC+MAO hybrid coatings. Meanwhile, PEC preprocessing also can afford an excellent micro-structure to increase the coating thickness as well as to improve the compactness of the PEC+MAO hybrid coatings. During the fabrication process of the PEC+MAO hybrid coatings, an overlapping phenomenon in regard to coating thickness can be observed instead of heaping up layer by layer. Compared with both single PEC surface modification layers as well as single MAO coatings, the PEC+MAO hybrid coatings exhibit more superior anti-corrosion property. Especially, the EIS data reveal that the PEC+MAO hybrid coatings can act as an effective protection system to provide relatively excellent long-range anti-corrosion protection. Note also that employing same MAO technique for both single MAO treatment as well as PEC+MAO combining procedure is the key to this research.

A Decade of Progress on MAO-Treated Tantalum Surfaces: Advances and Contributions for Biomedical Applications.

Micro-structured coatings with functional properties have been investigated due to a wide range of applications. It is known that micro-structures can play an important role in surface interactions determining the materials’ performance. Amongst the other materials, there has been an increasing interest in tantalum oxide (Ta2O5). This attention is mainly due to its variety of properties: biocompatibility and bioactivity; high dielectric constant; good thermal and chemical stability; excellent corrosion and mechanical resistance. Moreover, there is a wide range of applications in which the properties can be fitted. Furthermore, according to the final application, these properties can be enhanced or tailored through surface micro-structures manipulation. Due to this purpose, over the past decade, Ta surface modification by micro-arc oxidation (MAO) has been investigated mostly for biomedical applications. Therefore, this review focuses on Ta surface functionalization using the MAO technique. A clear understanding of the micro-discharge phenomena and the formation mechanism of a Ta2O5 anodic coating by MAO is supplied. The Ta2O5 coating morphology, topography, chemistry, and structure are explored, establishing their correlation with the MAO parameters. Additionally, an understanding of Ta2O5’s biological, mechanical, and electrochemical properties is provided and reviewed.

Improving structure and corrosion resistance of micro-arc oxidation coatings formed on aluminum alloy with the addition of La2O3

Abstract Ceramic coatings were prepared on 6061 aluminum alloy in electrolytes containing La2O3 particles using the micro-arc oxidation technique. The main work focuses on the microstructure, phase composition, elemental distribution and corrosion resistance of micro-arc oxidation coatings. The results showed that the addition of La2O3 increased the oxidation voltage and promoted the formation rate. Scanning electron microscopy observations indicated that the quantity of discharge micropores decreased and the thickness increased, and thus, the microhardness increased. The X-ray diffraction results showed that the coatings mainly consisted of γ-Al2O3, α-Al2O3 and SiO2. Electrochemical corrosion tests showed that the corrosion resistance of the coated sample with La2O3 increased greatly because the addition of La2O3 significantly reduced the micropores of the coating surface and made the coating thicker, smoother and harder. Hence, the addition of La2O3 can optimize the structure of the micro-arc oxidation coating and improve its corrosion resistance.