Micro-arc Oxidation Surface Research Articles

Design of the Micro-Arc Oxidation Surface Protection GTAW Integrated Pulse Power

Design a welding and micro-arc oxidation integrated pulse power toward micro-arc oxidation problems of the welding parts of aluminum, magnesium, titanium and its alloy, which can achieve the samples surface protection after welding. Adopting modular design, by adjusting PWM inverter buck and high-frequency inverter boost to get the setting voltage value, the power supplying current and voltage value via chopper inverter to realize. The hardware of system makes STM32 as the core, using CPLD as the basis to design the power control system. Software based on block control strategy applying DA to control the power parameters. Load test proved the feasibility of the power supply design. The power supply can output stable operating parameters. Polarization curve test indicated that the power supply improve the corrosion resistance of the weld joint.

Modification of Mg Alloy Surfaces Based on Micro-Arc Oxidation Methods

Chemically and mechanically protective coatings are formed on surface of Magnesium alloys by micro-arc oxidation (MAO) methods. Modification of the obtained MAO surfaces was made in two aspects. Firstly, the protection is enhanced by forming super-hydrophobic surfaces, with water contact angle higher than 120o, attributed to hierarchical nanomicro structures. The overall process involves alkaline etching to form nanoscale structures on top of micro-porous surface achieved during micro-arc oxidation processes. Secondly, the electrical property of the MAO surfaces is modified. A film with electrical conductivity of 2.4Ω/sq is achieved by Ni deposition and characterized by four point probe measurement. The morphology, phase, and chemical composition of all surfaces are investigated by SEM, AFM, and XRD analysis.

Surface Modifications of Mg Alloys Based on Micro-Arc Oxidation Methods from Manufacturing Perspectives

Chemically and mechanically protective coatings are formed on surface of Magnesium alloys by micro-arc oxidation (MAO) methods. From manufacturing perspectives, modification of the obtained MAO surfaces was made in two aspects. Firstly, the protection is enhanced by forming super-hydrophobic surfaces, with water contact angle higher than 120o, attributed to hierarchical nanomicro structures. The overall process involves alkaline etching to form nanoscale structures on top of micro-porous surface achieved during micro-arc oxidation processes. Secondly, the electrical property of the MAO surfaces is modified. A film with electrical conductivity of 2.4Ω/sq is achieved by Ni deposition and characterized by four point probe measurement. The morphology, phase, and chemical composition of all surfaces are investigated by SEM and XRD analysis.

Characterization and In Vitro Bioactivity of Calcium and Phosphorous Containing Titania Layer on Ti6Al4V Alloy

Calcium and phosphorous containing titania layers on Ti6Al4V biomedical alloy were formed by micro arc oxidation (MAO) in an electrolyte containing calcium acetate and sodium phosphate, and then subjected to hydrothermal treatment (HT) in order to achieve improved biocompability with modified titania layer. Samples were hydrothermally treated in water solution whose pH was adjusted to 11.0-11.5 by adding NaOH, at 230 °C for 10 h and cooled in the autoclave . Surface morphology, microstructure, and phase com position of titania layer were investigated systematically before and after HT. Their biomimetic apatite inducing ability in a simulated body fluid (SBF) was investigated. The bioactivity tests of modified MAO surface on Ti6Al4V alloy showed a considerable improvement compared to the unmodified MAO surface. Abstract: Ti6Al4V biomedikal titanyum alasimi uzerinde kalsiyum asetat ve sodyum fosfat iceren elektrolit icinde gerceklestirilen mikro ark oksidasyon islemi ile kalsiyum ve fosfor iceren titanyum oksit tabakasi olusturulmustur. Olusturulan oksit tabakasinin biyomimetik apatit olusturma ozelligini iyilestirmek amaciyla numuneler 10 saat sureyle 230 °C'de sodyum hidroksit iceren sulu cozelti icerisinde hidrotermal isleme maruz birakilmistir. Numunelerin yu zey morfolojileri, oksit tabakalarin mikroyapisi ve faz kompozisyonlari hidrotermal islem oncesi ve sonrasinda incelenmistir. Numunelerin biyomimetik apatit olusum karakteristigi incelemesi yapay vucut sivisi icinde gerceklestirilmistir. Mikro ark oksidasy on islemini takiben uygulanan hidrotermal islem sonucunda Ti6Al4V numunenin yuzeyinde biyomimetik apatit olusumunun iyilestigi gozlemlenmistir.

Effect of voltage on microstructure and corrosion resistance of microarc oxidation coatings on CP-Ti

The surface modification of commercially pure titanium (CP-Ti) by microarc oxidation (MAO) under different voltages was investigated using 1%H3PO4 solution as an electrolyte. The microstructure, phase composition and elemental distribution of ceramic coatings were investigated using scanning electron microscopy (SEM) and X-ray diffraction. The corrosion behaviour of the coating was also examined by potentiodynamic polarisation testing in a 3·5 wt-%NaCl solution. Micropore oxide films were formed on all the sample groups by MAO. The thickness and micropore size of the MAO coating increased with the increasing voltage. Energy dispersive X-ray spectroscopy results indicate that Ti, O and P became incorporated into the MAO coatings. At a low voltage of 250 V, the MAO coatings were composed of amorphous, P2O5, TiP2O7 and titania phases (rutile and anatase). Variation of treatment voltages increased the ceramic coatings from an amorphous structure to a phase structure, and the P2O5 phase disappeared. The corrosion potential Φcorr of the MAO sample shifted towards nobler directions, and the corrosion density Icorr fell significantly compared with that of the bare CP-Ti. Corrosion testing showed that the sizes of the micropore of the MAO samples obviously decrease, and the MAO surface becomes smooth.

Surface characterization and corrosion behavior of micro-arc oxidized Ti surface modified with hydrothermal treatment and chitosan coating

In the present work, we describe the surface modification of commercially pure titanium (CP-Ti) by a composite/multilayer coating approach for biomedical applications. CP-Ti samples were treated by micro-arc oxidation (MAO) and subsequently some of the samples were coated with chitosan (Chi) by dip coating method, while others were subjected to hydrothermal treatment (HT) followed by chitosan coating. The MAO, MAO/Chi, and MAO/HT/Chi coated Ti were characterized and their characteristics were compared with CP-Ti. X-ray diffraction and scanning electron microscopy were used to assess the structural and morphological characteristics. The average surface roughness was determined using a surface profilometer. The corrosion resistance of untreated and surface modified Ti in commercial saline at 298K was evaluated by potentiodynamic polarization test. The results indicated that the chitosan coating is very well integrated with the MAO and MAO/HT coating by physically interlocking itself with the coated layer and almost sealed all the pores. The surface roughness of hydrothermally treated and chitosan coated MAO film was superior evidently to that with other sample groups. The corrosion studies demonstrated that the MAO, hydrothermally treated and chitosan coated sample enhanced the corrosion resistance of titanium. The result indicates that fabrication of hydrothermally treated MAO surface coatings with chitosan is a significant approach to protect the titanium from corrosion, hence enhancing the potential use of titanium as bio-implants.

MicroRNA Functionalized Microporous Titanium Oxide Surface by Lyophilization with Enhanced Osteogenic Activity

Developing biomedical titanium (Ti) implants with high osteogenic ability and consequent rigid osseointegration is a constant requirement from the clinic. In this study, we fabricate novel miRNA functionalized microporous Ti implants by lyophilizing miRNA lipoplexes onto a microporous titanium oxide surface formed by microarc oxidation (MAO). The microporous titanium oxide surface provides a larger surface area for miRNA loading and enables spatial retention of the miRNAs within the pores until cellular delivery. The loading of lipoplexes into the micropores on the MAO Ti surface is facilitated by the superhydrophilicity and Ti-OH groups gathering of the MAO surface after UV irradiation followed by lyophilization. A high miRNA transfection efficiency was observed in mesenchymal stem cells (MSCs) seeded onto the miRNA functionalized surface with no apparent cytotoxicity. When functionalizing the Ti surface with miR-29b that enhances osteogenic activity and antimiR-138 that inhibits miR-138 inhibition of endogenous osteogenesis, clear stimulation of MSC osteogenic differentiation was observed, in terms of up-regulating osteogenic expression and enhancing alkaline phosphatase production, collagen secretion and ECM mineralization. The novel miRNA functionalized Ti implants with enhanced osteogenic activity promisingly lead to more rapid and robust osseointegration of a clinical bone implant interface. Our study implies that lyophilization may constitute a versatile method for miRNA loading to other biomaterials with the aim of controlling cellular function.

Bone Augmentation in a Titanium Cap with a Porous Surface Modified by Microarc Oxidation

To compare bone augmentation on pure titanium-machined surfaces and surfaces that have been modified by microarc oxidation (MAO) using titanium caps. Twenty caps were manufactured from rods of commercially pure titanium. The control group (CG) consisted of 10 titanium caps with machined inner walls. The test group (TG) consisted of 10 titanium caps that were modified by MAO in an electrolyte solution containing calcium phosphate ions. The two types of titanium caps were fixed on the calvaria of 10 New Zealand rabbits. Each rabbit received two different caps. Although each cap was unfilled, the marrow and blood from the wound of the rabbit skulls could penetrate into the caps. After 4 weeks, the rabbits were sacrificed, and the skulls were removed for observation. The zenith of new bone was measured directly after the caps were removed from the skulls; subsequently, the bone volume was calculated by microcomputed tomography. Little bone augmentation could be observed in the CG caps, and the new bone height of the CG group was inconspicuous. In contrast, the new bone extended along the inner walls of the TG caps. The mean height of new bone of the TG group was 2.3 ± 0.28 mm. The mean volume of new bone in the TG group was 18.63 ± 3.80 mm(3). New bone formation in a titanium cap surface modified by MAO was greater than that of a nonmodified cap. A titanium cap allowed new bone formation on the MAO surface to be observed and is a promising device for bone augmentation. Additionally, this finding suggests that observation through a titanium cap is a feasible method for biomaterial testing in hard tissue.

Effects of irradiation on osteoblast‐like cells on different titanium surfaces in vitro

The aim of this study was to investigate the effects of irradiation on adhesion ability, proliferation, and differentiation of MC3T3-E1 cells on microarc oxidation (MAO) titanium surfaces and polished titanium (PT) surfaces. MC3T3-E1 cells were exposed to a single dose at 2, 4, 6, 8, or 10 Gy using a (60) Co source, with tissue culture polystyrene plates chosen as controls. On all surfaces, irradiation resulted in a dose-dependent decrease in cellular proliferation. At 4 Gy dose, the cell proliferation of cells decreased by 17.8% on MAO and 18.6% on PT surfaces, respectively, compared with nonirradiated controls. Cells exposed to 8 Gy dose showed significant inhibition in collagen secretion and osteogenesis-related genes expression (OSX, COL-Iα1, and OCN). In contrast, irradiation increased cell adhesion to three surfaces dose dependently. It was also demonstrated that cells on MAO surface showed higher adhesion and collagen secretion than on PT surface at different radiation doses. This study revealed the effects of irradiation on osteoblasts in vitro on two titanium surfaces. MAO surface could be used in dental implants in irradiated bone due to enhanced adhesion ability and collagen secretion in osteoblasts.

Effect of micro-arc oxidation surface modification on the properties of the NiTi shape memory alloy

In this paper, the effects of micro-arc oxidation (MAO) surface modification (alumina coatings) on the phase transformation behavior, shape memory characteristics, in vitro haemocopatibility and cytocompatibility of the biomedical NiTi alloy were investigated respectively by differential scanning calorimetry, bending test, hemolysis ratio test, dynamic blood clotting test, platelet adhesion test and cytotoxicity testing by human osteoblasts (Hobs). The results showed that there were no obvious changes of the phase transformation temperatures and shape memory characteristics of the NiTi alloy after the MAO surface modification and the coating could withstand the thermal shock and volume change caused by martensite-austenite phase transformation. Compared to the uncoated NiTi alloys, the MAO surface modification could effectively improve the haemocopatibility of the coated NiTi alloys by the reduced hemolysis ratio, the prolonged dynamic clotting time and the decreased number of platelet adhesion; and the rough and porous alumina coatings could obviously promote the adherence, spread and proliferation of the Hobs with the significant increase of proliferation number of Hobs adhered on the surface of the coated NiTi alloys (P < 0.05).

Mineralized and osteoid tissue from dental pulp stem cells on micro-arc oxidation titanium in vitro

The presence of insufficient bone volume affects the implant healing and success. The aim of this study was to evaluate osteogenic capacity of dental pulp stem cells (DPSCs) on micro-arc oxidation (MAO) titanium surface. DPSCs were challenged at MAO and smooth titanium surface separately for different durations, and the bone marrow mesenchymal stem cells (BMSCs) served as the positive controls. The osteogenic capacity of DPSCs on MAO titanium surface was assessed by using scanning electron microscopy, energy dispersive spectroscopy, biochemical tests and real-time quantitative PCR. Data showed that DPSCs differentiated into osteoblasts and expressed bone morphogenetic genes on MAO titanium surface. The results of this study revealed that DPSCs had good potential to generate mineralized tissue on MAO titanium plates. The differential potential of DPSCs may be regulated by MAO titanium surface. The osteogenesis potential of DPSCs on the MAO titanium was similar with BMSCs.

Formation and Infrared Emissivity of Microarc Oxidation Coatings on Mg-7Li Alloy

Ceramic coatings were successfully fabricated on Mg-7Li alloy in Na2SiO3 electrolyte by microarc oxidation (MAO). The phase composition, formation mechanism and infrared emissivity of the coatings were investigated. Results show that the surface of MAO coating exists some micropores with a diameter of 2-6μm due to electric breakdown. The MAO coating with 13μm thickness is mainly composed of MgO, Li2O2 and Mg2SiO4. The infrared emissivity of the MAO coating is higher than that of bare Mg-7Li alloy, mainly because the coating consisting of ionic crystals has lower lattice vibration symmetry and larger dipole moment.

Effect of different wave-length ultraviolet light-treated micro-arc oxidation titanium surfaces on the physicochemical properties and bioactivity in vitro

To study the effects of ultraviolet (UV) light-treatment on the physicochemical properties and bioactivity of micro-arc oxidation (MAO) titanium surfaces in vitro. The pure titanium were prepared using MAO. MAO titanium samples were treated with 15 W bactericidal lamp UVC [λ = (250 ± 20) nm] or 15 W mercury lamp [λ = (360 ± 20) nm] for 24 h under ambient conditions. Three sample groups were prepared: MAO, UVA treated after MAO (MAO + UVA), UVC treated after MAO (MAO + UVC). The surface physicochemical properties were evaluated using scanning electron microscopy (SEM), contact angle measuring device, energy dispersive X-ray spectrometer (EDX), and X-ray diffraction (XRD). Bicinchoninic acid (BCA) based colorimetric detection was used to quantify the percentage of albumin adsorption after 2 h, 6 h, and 24 h incubation on the titanium surfaces. The rates of MG-63 cells attached to each group titanium surfaces were calculated by nucleus immunofluorescence using Hoechst 33342 after 1 h, 2 h, and 4 h incubation. SEM was used to observe cell morphology on titanium surfaces in each group. No obvious differences in surface topography, TiO(2) crystal and elemental composition were detected on titanium surfaces with or without UV treatment. Statistically significant difference in contact angles among MAO + UVC group (65.34 ± 1.16)°, MAO + UVA group (44.64 ± 1.28)°, and MAO group (3.41 ± 0.48)° were found (P < 0.001). The percentage of albumin adsorption reached the plateau after 2 h incubation on MAO + UVC titanium surfaces (48.16 ± 1.24)%, which was higher than those in MAO [(8.22 ± 2.99)%] and MAO + UVA groups [(5.29 ± 2.27)%, P < 0.001]. The rates of cells attached to the surfaces of MAO + UVC titanium was greater than that on MAO surfaces and MAO + UVA surfaces after 1 h [(40.71 ± 4.08)%], 2 h [(53.72 ± 2.38)%], 4 h [(70.32 ± 2.85)%] incubation (P < 0.05). The MAO + UVC surfaces remarkably enhanced the spread of MG-63 cells, however, there was no significant difference between the group of MAO and MAO + UVA. Pretreatment of micro-arc oxidation titanium with UVC light considerably improved the surface bioactivity to MG-63 cells, which showed an increase in cellular attachment and spread.

The influence of UV irradiation on the biological properties of MAO-formed ZrO2

Zirconium and its alloys are thought to be ideal materials for dental and orthopedic implants. However, the surface of native zirconium is bio-inert. It has been reported that micro-arc oxidation (MAO) is a convenient and effective method to improving the biocompatibility and bioactivity of the zirconium surface, and ultraviolet (UV) irradiation can improve the bioactivity of the MAO-formed ZrO2 without altering its surface morphology, grain size and phase component. The aim of the present study was to evaluate the influence of UV irradiation on the biocompatibility and bioactivity of MAO-formed ZrO2. Two types of samples were established. Those formed by MAO were labeled as MAO ZrO2 samples, while those that underwent UV irradiation after MAO treatment were labeled as MAO-UV ZrO2 samples. In the in vitro study, osteoblasts were seeded on the surfaces of the MAO and MAO-UV samples and were then studied by inverted phase contrast microscopy, scanning electron microscope (SEM) and MTT (3-(4.5-dimethyl-2-thiazolyl)-2.5-diphenayl-2H-tetrazolium bromide) testing. While in the in vivo study, the samples were implanted into calvarias of New Zealand white rabbits and were then evaluated by histology and shear strength analysis. The results indicated that the MAO-UV surfaces showed better biocompatibility, faster new bone formation and firmer bonds with bone than the MAO surfaces. Therefore, UV irradiation may be an optimal second-stage treatment that can improve the properties of MAO-formed ZrO2.

(Al 2 O 3 -SiO 2 ) sf /AZ91D镁基复合材料微弧氧化膜的制备及电化学阻抗谱分析 制备及电化学阻抗谱分析

A thick protective ceramic coating on 33% (Al2O3-SiO2)sf/AZ91D (volume fraction) magnesium matrix composite was prepared by the microarc oxidation (MAO) technique in silicate electrolyte. SEM, EDS and XRD were employed to analyze the surface morphology, composition and phase constituent of the coating, furthermore, the microhardness profile of the coating was also measured. The electrochemical corrosion properties of magnesium matrix composite before and after the MAO surface treatment were evaluated by electrochemical impedance spectroscopy (EIS), and the equivalent circuits corresponding to different immersion times were suggested. The results show that the fiber-reinforced composite surface is completely covered by the MAO coating. The ceramic coating mainly consists of MgO and Mg2SiO4 phases. The maximum microhardness of coating is up to

Microstructure and Corrosion Resistance Behavior of Composite Micro-Arc Oxidation and Sio&lt;sub&gt;2&lt;/sub&gt; Coatings on Magnesium Alloys

SiO2 sol sealing agent was developed by hydrolyzing of organic alkoxide, and protective composite coatings were obtained on magnesium alloys AZ31B by micro-arc oxidation (MAO) treatment plus a top coating with sealing agent using dipping-costing technique. SEM observations revealed that SiO2 sol immersed into pores and uniformly covered the surface of MAO coating. XPS analysis indicated that an inorganic SiO2 layer has formed on the surface of MAO coating. The results of potentiodynamic polarization tests showed that corrosion resistance of AZ31B alloys with composite coatings was evidently superior to that of merely MAO coating. The SiO2 layer provided corrosion protection by physically sealing the pores on the MAO coating and acting as a barrier. The composite coatings could suppress the corrosion process by preventing the transferring or diffusing of corrosive ions between magnesium alloys substrate and solution.

Bioactivity and corrosion properties of novel coatings containing strontium by micro-arc oxidation

Pure titanium (Ti) and titanium alloys are considered as bio-inert materials in clinical use. Bioactivity is the ability to induce bone-like apatite on the material surface. The micro-arc oxidation (MAO) technique is an effective method for improving the surface properties of titanium. The aim of this study was to investigate the bioactivity and corrosion behavior of MAO coatings containing strontium, which is beneficial for biological performance. The bioactivity of materials was evaluated based on the ability to induce a bond-like apatite layer on the surface in simulated body fluid (SBF), as proposed by Kokubo et al. After the materials were soaked in SBF for 1 day, precipitates formed on the surface of MAO coating. The surface of MAO coatings was completely covered with precipitates after 7 days. The precipitates, which were found to be composed of fiber structures, were identified as the apatite phase using thin film X-ray diffraction (TF-XRD). The results show that MAO coatings containing strontium can induce the formation of an apatite layer on their surface. In the potentiodynamic test, MAO coatings exhibited a more noble corrosion potential ( E corr) than that of titanium in SBF. In the passive region, the current density of MAO coatings was lower than that of titanium. All findings in this study indicated that MAO coatings containing strontium have good bioactivity and corrosion resistance for clinical applications.

Anti-corrosion microarc oxidation coatings on SiC P/AZ31 magnesium matrix composite

The corrosion-resistant ceramic coatings up to 80 μm thick were fabricated on SiC P/AZ31 magnesium matrix composite by microarc oxidation (MAO) technique in Na 3PO 4 + KOH + NaF solution. The microstructure, composition and phase constituent of ceramic coatings were analyzed by SEM and XRD, and the electrochemical corrosion behaviour of coatings was evaluated by the electrochemical polarization method. The thicker coating is compact and displays a good adhesion to the composite substrate. The ceramic coatings consist of MgO, Mg 2SiO 4, MgF 2, Mg 3(PO 4) 2, furthermore, a few residual SiC phases were also found in the coatings by means of SEM observation and EDX analysis. Most of SiC reinforced particles in the oxidized composite substrate have transformed into the oxides under microarc discharge sintering, but a few residual SiC reinforcements in the MAO coatings have not disrupted the continuity of coatings. So the corrosion resistance of the SiC P/AZ31 composite is greatly improved by MAO surface treatment, however, the corrosion resistance of coated composite also depends on the coating thickness.

Microstructure and phase composition of microarc oxidation surface layers formed on aluminium and its alloys 2214-T6 and 7050-T74

The influence of substrate on the microstructure and phase composition of surface layers synthesised by microarc oxidation (MAO) on aluminium and its alloys 2214-T6 and 7050-T74 is studied using scanning (SEM) and transmission electron microscopy (TEM) as well as cross-sectional X-ray diffraction. MAO layers are composed of three layers and are mainly made of gamma-Al 2O 3 and alpha-Al 2O 3 phases. The proportion of each phase depends on the substrate. The external porous layer is mainly composed of the gamma-Al 2O 3 phase. The internal dense layer can present two aspects according to the percentage of the alpha-Al 2O 3 phase. The so-called granular aspect indicates a high proportion of “dendrite” defect which results from discharge formation and implies a high percentage of the alpha-Al 2O 3 phase. The so-called columnar aspect indicates a high proportion of “small channels” associated with a very weak percentage in the alpha-Al 2O 3 phase. In the latter, it is believed that a Zn alloying element can inhibit the growth of alpha-Al 2O 3. During the MAO process, discharges likely occur in the vicinity of the MAO layer/substrate interface, probably in the spherical porosities that result from oxygen generated in the thin layer localised at the interface.

Initial osteoblast functions on Ti‐5Zr‐3Sn‐5Mo‐15Nb titanium alloy surfaces modified by microarc oxidation

This study is intended to evaluate the effects of microarc oxidation (MAO) on the biocompatibility of near beta titanium alloy Ti-5Zr-3Sn-5Mo-15Nb (TLM) in vitro. Two porous bioactive surfaces with different surface characteristics were grown on TLM substrates via MAO process at two different final voltages. Both calcium and phosphorus were incorporated into the oxidized surfaces, and their content was dependent on the voltage applied. Surface roughness was enhanced on the MAO surfaces, which was higher when a higher voltage was applied. After MAO treatment, water contact angles became smaller and surface energies were increased, especially the polar components, which were also related to the MAO final voltage. Cell culture experiments showed an enhanced osteoblasts adhesion, spread, and viability on the microarc oxidized surfaces, and better cell spread and viability were found on the surface formed at 450 V than that at 300 V. No obvious variations in gene expression of integrin beta1 (Itg beta 1), core binding factor-alpha1, osteopontin, collagen type I alpha2-chain, and fibronectin by osteoblasts were observed on different surfaces. The expression of osteocalcin was strikingly increased on MAO surfaces after 72 h, thus indicating enhanced osteoblasts differentiation on MAO surfaces. Interestingly, obvious enhanced bone morphogenetic proteins (BMP)-2 and BMP-4 expression was observed on MAO surfaces, which may be a reason for the enhanced osteoblasts functions on MAO-modified TLM surfaces.