Papers by Keyword: Micro-Arc Oxidation (MAO)

Abstract: Micro-arc oxidation (MAO) is known as a novel technique to use for the modifying the surface of valve metal, which improve mechanical and corrosion resistance properties. In this study, MAO coatings are fabricated on ALZ magnesium lithium alloy to protect the substrate from corrosion using environmentally friendly electrolytes under a high voltage power supply. The Taguchi method is used to identify the effects of current density, coating time and electrical frequency on the thickest coating uniformity. The optimum coating properties are characterized by coating thickness measurement, Scanning electron microscopy (SEM), Potentiodynamic polarization analysis. It was found that the processing time is the main factor affecting the thickest coating uniformity (t_u). Coatings fabricated under optimum conditions are in close agreement with the predicted values of Taguchi analysis. The corrosion resistance of MAO coated on ALZ magnesium lithium alloy are greatly improved compare to the bare alloy in corrosive environments.

Abstract: Formation mechanism of the micro-arc oxidation spark discharge is always a research problem; so far there isnt a theoretical model for analyzing the spark discharge formation which is widely recognized. Based on analyzing the reaction phenomena and the coating feature in the different periods of the red spark discharge, the formation model of the red spark discharge was established. The spark discharge formation mechanism is shown that it causes the spark discharge formation that the electron bombards the gas layer wrapping the coating in the infancy of red spark discharge stage; at the later period the area of strong electric field generates the spark discharge where the coating of excessive polarization turns out easily.

Abstract: Autogenous single pass full penetration welds of 2.8 mm thick AA 2014 plates were produced by un-pulsed and pulsed gas tungsten arc welding (GTAW) process. In pulsed current mode, two levels of pulsing viz., 3 and 6 Hz were employed. In order to improve the corrosion resistance of weld metals, micro arc oxidation (MAO) treatment was given in aqueous silicate solution containing either borax or tungstate. The MAO treatment was carried out for 10, 20 and 30 minutes. Irrespective of the electrolyte composition, surface roughness increased with increasing treatment duration. However, the effect was observed to be significant with borax addition. X-ray diffraction studies showed that γ-Al₂O₃ content in the coating continued to increase up to 20 minutes and for the coating produced with 30 minutes duration the α-Al₂O₃ content was found to be more than γ-Al₂O₃. The coating treated for 30 minutes exhibited relatively poorer corrosion resistance than the other coated specimens. The better corrosion resistance offered by the coating obtained after 20 minutes, compared with the other coatings, could be attributed to the nature of the oxide and its content. Even though tungstate addition improved hardness of the coating, borax addition was found to enhance the corrosion resistance.

Abstract: The present work is mainly focussed on studying the effect of electric pulse frequency and duty cycle on the structural, morphological and corrosion characteristics of micro arc oxidation (MAO) films developed for a fixed oxidation time of 2.5 min on Ti-6Al-4V biomedical implant material. For this purpose, the titania films are decisively developed under four different conditions arising from two levels of pulse duty cycle (10% and 75%) and frequencies (500 Hz and 1500 Hz). A phosphate based electrolyte system is employed for developing the titania films. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results demonstrated that though all the titania films are developed for the same oxidation time of 2.5 min, the rate of anatase to rutile phase transformation, the crystallite growth, the size and distribution of surface pores and film thickness of the titania film are strongly influenced by the electric pulse frequency and duty cycle. The potentiodynamic polarization (PDP) tests conducted under simulated body fluid (SBF) conditions (37 °C and 7.4 pH) showed that all the titania films could significantly improve the corrosion resistance of Ti-6Al-4V compared to that of the untreated alloy. Of all the titania films developed for the same oxidation time of 2.5 min, the one treated with 1500 Hz frequency and 75% duty cycle exhibited better corrosion resistance than those of the other films and the untreated Ti-6Al-4V implant material.

Abstract: To obtain optimal medical ceramic film with bioactivity, Microarc oxidized TiO2-based films containing Ca and P on titanium alloy were formed in electrolytes containing hydroxyapatite and β-tricalcium phosphate salts. After that the biocompatibility tests including invitro soaking test and invivo implant experiment were carried out, and component and phases of films were analysed by energy dispersive spectrometer and X-ray diffraction, respectively.The obtained result shows the porosity biomedical ceramic films with different proportional of Hydroxyapatite/β-tricalcium are fabricated through changing the electrolyte composions,respectively.The bioactivity of biphasic calcium phosphate is enhanced comparing to the pure HA ones.So the biphasic calcium phosphate film material can be satified with medical application.

Abstract: Titanium with surface nanostructure has superior mechanical and biological properties, which benefits titanium implants. To further improve the bioactivity of Ti surfaces, Ca/P-containing porous titania coatings were prepared on Ti with surface nanostructure by ultrasonic shot peening (USP) and micro-arc oxidation (MAO). The phase identification, composition, morphology and microstructure of the coatings of Ti with surface nanostructure during MAO were investigated subsequently. The amounts of Ca, P and the Ca/P ratio of the coatings formed on Ti with surface nanostructure were greater than those on coarse-grained Ti. Incubated in a simulated body fluid, bone-like apatite was completely formed on the surface of Ti, thus evidencing preferable bioactivity.

Abstract: Micro arc oxidation (MAO) is a relatively new method of surface treatments which has been used to improve the mechanical and tribological behavior of light metals. Due to the ceramic coating generated by MAO, light metals can be used more widely. The fundamental of MAO and the influence factors of MAO process are discussed here. The surface characteristics of aluminum, titanium, magnesium, Zirconium and stainless steels have been improved by MAO. Scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS) were used to study the surface morphology and the elemental composition of the MAO coating. The EDS analysis of the coating shows the elements in the electrolyte and oxygen have incorporated into the coating.

Abstract: This study used micro-arc oxidation technology for pure titanium alloy surface modification, which 400μm titanium beads were sintered into porous titanium in vacuum conditions, and produced silicon and calcium coatings. Scanning electron microscope(SEM), X-ray diffraction (XRD) and Energy dispersion spectrometer(EDS) were employed to investigate the surface morphology and phase composition of the coatings. The results are listed as follows: the main component of porous titanium MAO coating is anatase TiO2,and the coating introduced silicon and calcium element successfully. The proliferation ability of osteoblasts on the oxidized and unoxidized surface was determined by CCK-8 method, The results indicated that both the proliferation and adhesion ability of osteoblast on the oxidized surface were better than the unoxidized surface.

Abstract: In order to realize the application of finite element analysis in structural optimization of micro-arc oxidation electrode, effects of two kinds of electrode mode (one and two cathodes) on thickness and surface morphology of ceramic coatings prepared by micro-arc oxidation on aluminum alloy were researched by experiment. Meanwhile, Ansoft Maxwell finite element software was used to analysis the main influence factor (electric field intensity). We contrasted the analysis conclusion above with the forecast results in experiment. Effect of electric field intensity on thickness and surface morphology of ceramic coatings were explained from micro level, the correctness of the finite element analysis software was verified. The results show that three electrodes mode is better than two electrodes mode, the former can not only make the thickness of ceramic coatings thicker, but also make sure the size and quantity of discharge channel bigger and more, and growth power enough.

Abstract: Anodic titania film was synthesized by electrochemical micro plasma oxidation method in H₂SO₄/NH₄NO₃ electrolyte, and electrochemical anodizing was carried out at various electrolyte temperatures. The photocatalytic properties and surface characteristics of anodic titania film were investigated. For anodic titania film synthesized at higher electrolyte temperature, the specific surface area of anodic film and the anatase crystalline phase gradually increased. The anodic titania film fabricated in high temperature electrolyte showed not only a slight red shift related to increasing the anatase phase ratio but also a high efficiency of dye degradation.