Oxide ceramic coatings were fabricated on tantalum alloys by micro-arc oxidation (MAO) to improve their hardness and tribological properties. The MAO coatings were manufactured in a mixed silicatephosphate electrolyte...Oxide ceramic coatings were fabricated on tantalum alloys by micro-arc oxidation (MAO) to improve their hardness and tribological properties. The MAO coatings were manufactured in a mixed silicatephosphate electrolyte containing NaF and/or EDTA (ethylene diamine tetraacetic acid). The surface morphology,cross-sectional view, chemical composition, hardness, and wear performance of the coatings were analysed. As revealed by the scanning electron microscopy, silica-rich nodules appear on the MAO coating obtained in the silicate-phosphate electrolyte, but the formation of nodules is inhibited with NaF and/or EDTA in the electrolyte.Also, they reduce the roughness and improve the compactness of the coatings, which are composed of Ta_(2)O_(5),(Ta, O), and TaO. A thick and hard coating is obtained in the NaF-containing electrolyte, and the tribology performance is effectively improved. With additives, the nodule structure is detached from the coating surface and dissolved in the electrolyte. By using NaF as an electrolyte additive, the abrasion performance of the MAO coating is enhanced by decreasing the nodule structure, increasing the size of micropores, and improving the coating hardness.展开更多
Smart micro-arc oxidation(MAO)/epoxy resin(EP) composite coatings were formed on AZ31 magnesium(Mg) alloy. Mesoporous silica nanocontainers(MSN) encapsulated with sodium benzoate(SB) corrosion inhibitors were strategi...Smart micro-arc oxidation(MAO)/epoxy resin(EP) composite coatings were formed on AZ31 magnesium(Mg) alloy. Mesoporous silica nanocontainers(MSN) encapsulated with sodium benzoate(SB) corrosion inhibitors were strategically incorporated in the MAO micropores and in the top EP layer. The influence of the strategic positioning of the nanocontainers on the corrosion protective performance of coating was investigated. The experimental results and analysis indicated that the superior corrosion resistance of the hybrid coating is ascribed to the protection mechanisms of the nanocontainers. This involves two phenomena:(1) the presence of the nanocontainers in the MAO micropores decreased the distance between MSN@SB and the substrate, demonstrating a low admittance value(^5.18 × 10^(-8)Ω^(-1)), and thus exhibiting significant corrosion inhibition and self-healing function;and(2) the addition of nanocontainers in the top EP layer densified the coating via sealing of the inherent defects, and hence the coating maintained higher resistance even after 90 days of immersion(1.13 × 10^(10)Ω cm^(2)).However, the possibility of corrosion inhibitors located away from the substrate transport to the substrate is reduced, reducing its effective utilization rate. This work demonstrates the importance of the positioning of nanocontainers in the coating for enhanced corrosion resistance,and thereby providing a novel perspective for the design of smart protective coatings through regulating the distribution of nanocontainers in the coatings.展开更多
Micro-arc oxidation(MAO)is one of the promising methods to improve the corrosion resistance of magnesium alloys.However,there are plenty of micro-pores in the traditional MAO films,deteriorating their protection prope...Micro-arc oxidation(MAO)is one of the promising methods to improve the corrosion resistance of magnesium alloys.However,there are plenty of micro-pores in the traditional MAO films,deteriorating their protection property.A novel self-sealing pore MAO film was developed in this paper.The morphologies and chemical composition of the film were detected by scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDX).The corrosion behavior was investigated by electrochemical and salt spray tests.The possible film formation and corrosion mechanisms were proposed.The self-sealing pore film presents a blue appearance.Most of the micro-pores in the surface of the film are sealed during the film formation process.The chemical composition of the film mainly contains Mg,O,Ti,F and P.The self-sealing pore film exhibits better corrosion resistance compared with the traditional silicate film.Especially,the self-sealing pore film keeps intact after salt spray test for 2000 h,which can be attributed to its high compactness.展开更多
Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resist...Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resistance of the formed ceramic coatings were studied by SEM,XRD,and electrochemical methods,respectively. The results showed that the coatings produced in a sodium silicate solution system were composed of MgO and Mg2SiO4. The ceramic coating became thicker and the content of Mg2SiO4 phase increased as the concentration of Na2SiO3 increased in the solution. The coating was loose at the low concentration of Na2SiO3 and was compact at the high concentration of Na2SiO3. The coated samples had a better corrosion resistance than the Mg-Li substrate in terms of the Tafel polarization curves and the cyclic voltammetry curves (CV).展开更多
Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process a...Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.展开更多
The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MC...The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MCC)coatings on AZ91D magnesium alloys were prepared by Micro-arc Oxidation(MAO)and electrophoresis technologies.The microstructure,corrosion resistance,abrasion resistance,stone impact resistance and adhesion of MCC coatings were studied respectively.The cross section morphologies showed that the outer organic coating was filled into the hole on surface of MAO coating,and it acted as a shelter against corrosive products.The copper-accelerated acetic acid salt spray Test,abrasion resistance test,stone impact resistance test,thermal shock resistance test and adhesion test were used to evaluate the protective characterization by the third testing organization which approved by GM.The test results showed the composite coatings meet all the requirements.The MCC coating on Mg presents excellent properties,and it is a promising surface treatment technology on magnesium alloys for production vehicles.展开更多
The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. C...The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. Compared to constant electrolyte temperature in conventional MAO process, the process has different discharge characteristics under the changing electrolyte temperature. The amplitude of pulse voltage was detected to study the change of discharge characteristic under the constant-current control of MAO power supply. Three successive discharge stages were differentiated by the variable the pulse voltage versus process time. Since there were significant changes in the sound, the sound signals were acquired and the audio analysis was used to describe the changing of the MAO discharge at different stages. Optical emission spectroscopy (OES) was employed in situ to unveil how the micro-discharge changed with the temperature increasing. Scanning electron microscopy (SEM) was used to characterize the morphology of the coatings on 6N01 aluminum alloy prepared by normal process with the constant-temperature control of the MAO electrolyte and by the process under the changing electrolyte temperature. A mode of film growth and micro-discharge was given to describe the effects of the changing electrolyte temperature in the whole MAO process.展开更多
In order to prepare ornamental and anti-corrosive coating on aluminum alloys, preparation technology of black micro-arc ceramic coatings on Al alloys in silicate based electrolyte was studied. The influence of content...In order to prepare ornamental and anti-corrosive coating on aluminum alloys, preparation technology of black micro-arc ceramic coatings on Al alloys in silicate based electrolyte was studied. The influence of content of Na2WO4 and combination additive in solution on the performance of black ceramic coatings was studied; the anticorrosion performances of black ceramic coatings were evaluated through whole-immersion test and electrochemical method in 3.5% NaCl solution at different pH value; SEM and XRD were used to analyze the surface morphology and phase constitutes of the black ceramic coatings. Experimental results indicated that, without combination additives, with the increasing of Na2WO4 content in the electrolyte, ceramic coating became darker and thicker, but the color was not black; after adding combination additive, the coating turned to be black; the black ceramic coating was multi-hole form in surface. There was a small quantity of tungsten existing in the black ceramic coating beside α-Al2O3 phase and β-Al2O3 phase. And aluminum alloy with black ceramic coating exhibited excellent anti-corrosion property in acid, basic and neutral 3.5% NaCl solution.展开更多
Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relatio...Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.展开更多
Micro-arc oxidation(MAO)coating was prepared on Ti6Al4V alloy surface and its characterizations were detected by Vickers hardness tester,profilometer,scanning electric microscope(SEM),energy dispersive X-ray spectrome...Micro-arc oxidation(MAO)coating was prepared on Ti6Al4V alloy surface and its characterizations were detected by Vickers hardness tester,profilometer,scanning electric microscope(SEM),energy dispersive X-ray spectrometer(EDX)and X-ray diffractometer(XRD).Fretting wear behaviors of the coating and its substrate were comparatively tested without lubrication under varied displacement amplitudes(D)in a range of 3-40μm,constant normal load(Fn)of 300 N and frequency of 5 Hz.The results showed that the MAO coating,presenting rough and porous surface and high hardness,mainly consisted of rutile and anatase TiO2 phases.Compared with the substrate,the MAO coating could shift the mixed fretting regime(MFR)and slip regime(SR)to a direction of smaller displacement amplitude.In the partial slip regime(PSR),lower friction coefficients and slight damage appeared due to the coordination of elastic deformation of contact zones.In the MFR,the friction coefficient of the coating was lower than that of the substrate as a result of the prevention of plastic deformation by the hard ceramic surface.With the increase of the displacement amplitude,the degradation of the MAO coating and the substrate increased extremely.The fretting wear mechanisms of the coating were abrasive wear and delamination with some material transfer of specimen.In addition,the coating presented a better property for alleviating fretting wear.展开更多
Samples with two different shapes of 2024 aluminum alloy were treated with micro-arc oxidation (MAO), and the formation process and mechanism of oxidation film was analyzed. The results show that different geometrical...Samples with two different shapes of 2024 aluminum alloy were treated with micro-arc oxidation (MAO), and the formation process and mechanism of oxidation film was analyzed. The results show that different geometrical curvature of the material has an influence upon the uniformity of films and the corrosion-resistance.展开更多
Firstly, an aluminum coating was produced metallurgically on mild steel by hot-dipping, then an aluminum oxide coating was formed self-growingly from the aluminum coating by micro-arc oxidation treatment. The structur...Firstly, an aluminum coating was produced metallurgically on mild steel by hot-dipping, then an aluminum oxide coating was formed self-growingly from the aluminum coating by micro-arc oxidation treatment. The structures of the composite coatings were investigated by means of SEM, TEM and XRD. The results show that the composite coating consists of three layers which are Fe-Al alloy, aluminum coating and aluminum oxide orderly outward from the steel substrate. There are amorphous phases, k-Al2O3 and θ-Al2O3 mainly in the aluminum oxide.展开更多
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....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.展开更多
Ceramic coatings were prepared on Ti-6AI-4V alloy using ac micro-arc oxidation (MAO) in silicate-hypophosphate solution. Growth regularity and formation mechanism of ceramic coatings were discussed. It was found that ...Ceramic coatings were prepared on Ti-6AI-4V alloy using ac micro-arc oxidation (MAO) in silicate-hypophosphate solution. Growth regularity and formation mechanism of ceramic coatings were discussed. It was found that during the first stage the growth rate of coatings toward the external surface was larger than that toward substrate and then the coating began to grow mainly towards Ti alloy. When the total coating thickness reaches a certain value, it would no longer increase. In addition, the variations of the composition and microstructure of ceramic coatings according to the depositing time were also investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM).The amount of rutile TiO2 gradually increased, whereas the amounts of the anatase TiO2 and amorphous phases first increased and then decreased slightly.展开更多
Micro-arc oxidation(MAO)process was carried out in an optimized dual electrolyte system to fabricate a compact,smooth,and corrosion resistant coating on ZK60 Mg alloy.The microstructural characteristics of coating wer...Micro-arc oxidation(MAO)process was carried out in an optimized dual electrolyte system to fabricate a compact,smooth,and corrosion resistant coating on ZK60 Mg alloy.The microstructural characteristics of coating were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).Test of mass loss was conducted at a 3.5%NaCl solution to assess the resistance to corrosion.The bonding strength between the coating and ZK60 substrate was evaluated using scratch experiment.The results reveal that MgAl2O4and MgO are the main phases of ceramic coating obtained in the dual electrolyte system.The corrosion rate of coating prepared in the optimized dual electrolyte is only 0.0061 gám-2áh-1,which demonstrates excellent corrosion resistance.This is mainly due to the compact,uniform coating with high bonding strength.展开更多
A ceramic layer was prepared on the surface of Al2O3f /ZL109 composites by means of micro-arc oxidation (MAO) technique. The surface morphology and phase constituent of the ceramic layer were analyzed using scanning e...A ceramic layer was prepared on the surface of Al2O3f /ZL109 composites by means of micro-arc oxidation (MAO) technique. The surface morphology and phase constituent of the ceramic layer were analyzed using scanning electron microscope and X-ray diffraction. The polarization curves of the composites before and after MAO treatment were measured and analyzed. The results showed that after Al2O3f /ZL109 composites were treated using MAO technique in silicate solution, the ceramic layer formed, and it was composed of Al, Si, and mullite phase. Al and Si came from Al alloy matrix of the composites, and the mullite phase formed in process of MAO. Al2O3 fiber in the composites affects the electric conductivity of the composites, the MAO reaction is promoted, and the ceramic layer forming on the composite material side is slightly thicker than that on the Al alloy side. After Al2O3f /ZL109 composites were treated using MAO technique, the corro- sion resistance of the composites is significantly improved.展开更多
Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation(MAO)in a silicate-aluminate electrolyte solution with additives including sodium citrate,graphite and sodium tungstate.The microstructures a...Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation(MAO)in a silicate-aluminate electrolyte solution with additives including sodium citrate,graphite and sodium tungstate.The microstructures and compositions were analyzed by SEM,EDX and XRD.The corrosion and wear properties of the coatings were investigated by potentiodynamic polarization and ball-on-disc wear test,respectively.The results show that the MAO coatings consist of WO3,Ti2O3,graphite and Al2O3 besides Al2TiO5 and Al2SiO5.With additives in the electrolyte,the working voltage at the micro-arc discharge stage decreases,and the ceramic coating gets smoother and more compact.The corrosion current density of MAO coating is much lower than that of TiAl substrate.It can be reduced from 9.81×10-8A/cm 2to 3.02×10-10A/cm 2 .The MAO coatings composed of hard Al2O3,WO3 and Ti2O3 obviously improve the wear resistance of TiAl alloy.The wear rate is-3.27×10-7g/(N·m).展开更多
In the NaAlO2-Na2SiO3 compound system, the ceramic coatings were prepared on magnesium alloy by mi-cro-arc oxidation. The morphology, phase composition, and thermal shock resistance of the ceramic coatings were studie...In the NaAlO2-Na2SiO3 compound system, the ceramic coatings were prepared on magnesium alloy by mi-cro-arc oxidation. The morphology, phase composition, and thermal shock resistance of the ceramic coatings were studied by scanning electron microscope, X-ray diffraction and thermal shock tests, respectively. The results showed that the ce-ramic coating contains MgO, MgAl2O4, as well as a little amount of Mg2SiO4. The thickness of the ceramic coatings in-creases with the current density increasing, when the current density is 12 A?dm?2, the thermal shock resistance of the produced ceramic coating is the best. The hardness of the ceramic coating is up to 10 GPa or so.展开更多
Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses.However,residual stresses in the surface coatings of structural components have adverse...Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses.However,residual stresses in the surface coatings of structural components have adverse effects on their properties,such as fatigue life,dimensional stability and corrosion resistance,etc.The micro-arc oxidation ceramic coatings are produced on the surfaces of6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW.A constant current density of4.4 0.1 A/dm2and a self-regulated composite electrolyte are used.The micro-arc oxidation treatment period ranges from 10 min to 40min,and the thickness of the ceramic coatings is more than 20μm.Residual stresses attributed toγ-Al2O3constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2ψmethod.The analysis results show that the residual stress in the ceramic coatings is compressive in nature,and it increases first and then decreases with micro-arc oxidation time increase.The maximum stress value is 1667±20 MPa for period of 20 min.Through analyzing the coating thickness,surface morphology and phase composition,it is found that the residual stress in the ceramic coatings is linked closely with the coating growth,the phase composition and the micro cracks formed.It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress.The heat treatment makes the residual compressive stress value decrease 1 378 MPa.The ultrasonic action even alters the nature of the residual stress,making the residual compressive stress change into a residual tensile stress.展开更多
微弧的氧化(毛) 是在电解质媒介的提高的化学工艺在阀门金属表面上获得涂层结构。毛在磷酸钠电解质获得的三氧化钛电影被调查。这些电影主要由在锐钛矿和金红石形式的 TiO_2 阶段组成并且在表面与 Na 和 P 元素充实。他们的导致磷灰石...微弧的氧化(毛) 是在电解质媒介的提高的化学工艺在阀门金属表面上获得涂层结构。毛在磷酸钠电解质获得的三氧化钛电影被调查。这些电影主要由在锐钛矿和金红石形式的 TiO_2 阶段组成并且在表面与 Na 和 P 元素充实。他们的导致磷灰石的能力在模仿的身体液体(SBF ) 被评估。在为超过 30 d 的 SBF 的 Whenimmersing，优先的 carbonated-hydroxyapatite 在这些电影的表面上被形成，它建议对待 MAO 的钛有有希望的积极生物回答。展开更多
基金Funded by the National Natural Science Foundation of China (No. 51905506)。
文摘Oxide ceramic coatings were fabricated on tantalum alloys by micro-arc oxidation (MAO) to improve their hardness and tribological properties. The MAO coatings were manufactured in a mixed silicatephosphate electrolyte containing NaF and/or EDTA (ethylene diamine tetraacetic acid). The surface morphology,cross-sectional view, chemical composition, hardness, and wear performance of the coatings were analysed. As revealed by the scanning electron microscopy, silica-rich nodules appear on the MAO coating obtained in the silicate-phosphate electrolyte, but the formation of nodules is inhibited with NaF and/or EDTA in the electrolyte.Also, they reduce the roughness and improve the compactness of the coatings, which are composed of Ta_(2)O_(5),(Ta, O), and TaO. A thick and hard coating is obtained in the NaF-containing electrolyte, and the tribology performance is effectively improved. With additives, the nodule structure is detached from the coating surface and dissolved in the electrolyte. By using NaF as an electrolyte additive, the abrasion performance of the MAO coating is enhanced by decreasing the nodule structure, increasing the size of micropores, and improving the coating hardness.
基金appreciate the financial support by the National Natural Science Foundation of China (52071191,52201077)the Natural Science Foundation of Shandong Province (ZR2022QE191)+1 种基金Elite Scheme of Shandong University of Science and Technology (0104060541123)Talent introduction and Research Start-up Fund of Shandong University of Science and Technology (0104060510124)。
文摘Smart micro-arc oxidation(MAO)/epoxy resin(EP) composite coatings were formed on AZ31 magnesium(Mg) alloy. Mesoporous silica nanocontainers(MSN) encapsulated with sodium benzoate(SB) corrosion inhibitors were strategically incorporated in the MAO micropores and in the top EP layer. The influence of the strategic positioning of the nanocontainers on the corrosion protective performance of coating was investigated. The experimental results and analysis indicated that the superior corrosion resistance of the hybrid coating is ascribed to the protection mechanisms of the nanocontainers. This involves two phenomena:(1) the presence of the nanocontainers in the MAO micropores decreased the distance between MSN@SB and the substrate, demonstrating a low admittance value(^5.18 × 10^(-8)Ω^(-1)), and thus exhibiting significant corrosion inhibition and self-healing function;and(2) the addition of nanocontainers in the top EP layer densified the coating via sealing of the inherent defects, and hence the coating maintained higher resistance even after 90 days of immersion(1.13 × 10^(10)Ω cm^(2)).However, the possibility of corrosion inhibitors located away from the substrate transport to the substrate is reduced, reducing its effective utilization rate. This work demonstrates the importance of the positioning of nanocontainers in the coating for enhanced corrosion resistance,and thereby providing a novel perspective for the design of smart protective coatings through regulating the distribution of nanocontainers in the coatings.
基金financial support by the National Natural Science Foundation of China(No.51171198)National Key Basic Research Program of China(No.2013CB632205)the International Science&Technology Cooperation Program of China(2011DFA50904).
文摘Micro-arc oxidation(MAO)is one of the promising methods to improve the corrosion resistance of magnesium alloys.However,there are plenty of micro-pores in the traditional MAO films,deteriorating their protection property.A novel self-sealing pore MAO film was developed in this paper.The morphologies and chemical composition of the film were detected by scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDX).The corrosion behavior was investigated by electrochemical and salt spray tests.The possible film formation and corrosion mechanisms were proposed.The self-sealing pore film presents a blue appearance.Most of the micro-pores in the surface of the film are sealed during the film formation process.The chemical composition of the film mainly contains Mg,O,Ti,F and P.The self-sealing pore film exhibits better corrosion resistance compared with the traditional silicate film.Especially,the self-sealing pore film keeps intact after salt spray test for 2000 h,which can be attributed to its high compactness.
文摘Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature,phase composition,and corrosion-resistance of the formed ceramic coatings were studied by SEM,XRD,and electrochemical methods,respectively. The results showed that the coatings produced in a sodium silicate solution system were composed of MgO and Mg2SiO4. The ceramic coating became thicker and the content of Mg2SiO4 phase increased as the concentration of Na2SiO3 increased in the solution. The coating was loose at the low concentration of Na2SiO3 and was compact at the high concentration of Na2SiO3. The coated samples had a better corrosion resistance than the Mg-Li substrate in terms of the Tafel polarization curves and the cyclic voltammetry curves (CV).
文摘Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.
基金Support from National Natural Science Foundation of China(Grant NO.51271144)as well as from the National Key Technologies Research and Development Program of China(Grant No.2011BAE22B05)is gratefully acknowledged.And thanks to General Motors research and development center for provided test equipment.
文摘The magnesium alloys attract the light-weight manufacture due to its high strength to weight ratio,however the poor corrosion resistance limits the application in automobile industry.The Micro-arc Composite Ceramic(MCC)coatings on AZ91D magnesium alloys were prepared by Micro-arc Oxidation(MAO)and electrophoresis technologies.The microstructure,corrosion resistance,abrasion resistance,stone impact resistance and adhesion of MCC coatings were studied respectively.The cross section morphologies showed that the outer organic coating was filled into the hole on surface of MAO coating,and it acted as a shelter against corrosive products.The copper-accelerated acetic acid salt spray Test,abrasion resistance test,stone impact resistance test,thermal shock resistance test and adhesion test were used to evaluate the protective characterization by the third testing organization which approved by GM.The test results showed the composite coatings meet all the requirements.The MCC coating on Mg presents excellent properties,and it is a promising surface treatment technology on magnesium alloys for production vehicles.
文摘The electrolyte temperature has a great influence on the performance of the coating prepared by micro-arc oxidation (MAO). The behavior of MAO discharge in the changing electrolyte temperature has been investigated. Compared to constant electrolyte temperature in conventional MAO process, the process has different discharge characteristics under the changing electrolyte temperature. The amplitude of pulse voltage was detected to study the change of discharge characteristic under the constant-current control of MAO power supply. Three successive discharge stages were differentiated by the variable the pulse voltage versus process time. Since there were significant changes in the sound, the sound signals were acquired and the audio analysis was used to describe the changing of the MAO discharge at different stages. Optical emission spectroscopy (OES) was employed in situ to unveil how the micro-discharge changed with the temperature increasing. Scanning electron microscopy (SEM) was used to characterize the morphology of the coatings on 6N01 aluminum alloy prepared by normal process with the constant-temperature control of the MAO electrolyte and by the process under the changing electrolyte temperature. A mode of film growth and micro-discharge was given to describe the effects of the changing electrolyte temperature in the whole MAO process.
基金This work was financially supported bythe Doctoral Foundation ofYanshan University(B41)theScience and Technology Foundation ofYanshan University(YDJJ0169).
文摘In order to prepare ornamental and anti-corrosive coating on aluminum alloys, preparation technology of black micro-arc ceramic coatings on Al alloys in silicate based electrolyte was studied. The influence of content of Na2WO4 and combination additive in solution on the performance of black ceramic coatings was studied; the anticorrosion performances of black ceramic coatings were evaluated through whole-immersion test and electrochemical method in 3.5% NaCl solution at different pH value; SEM and XRD were used to analyze the surface morphology and phase constitutes of the black ceramic coatings. Experimental results indicated that, without combination additives, with the increasing of Na2WO4 content in the electrolyte, ceramic coating became darker and thicker, but the color was not black; after adding combination additive, the coating turned to be black; the black ceramic coating was multi-hole form in surface. There was a small quantity of tungsten existing in the black ceramic coating beside α-Al2O3 phase and β-Al2O3 phase. And aluminum alloy with black ceramic coating exhibited excellent anti-corrosion property in acid, basic and neutral 3.5% NaCl solution.
基金Council of Scientific and Industrial Research (G8/19901/2013), New Delhi for the financial support provided to conduct this investigation through sponsored project No. 22(0615)/13/EMR-II dated 26.02.2013
文摘Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.
基金Project(50521503)supported by the National Natural Science Foundation of ChinaProject(2007CB714704)supported by the National Basic Research Program of ChinaProject(200536)supported by the Foundation of the Author of National Excellent Doctoral Dissertation of China
文摘Micro-arc oxidation(MAO)coating was prepared on Ti6Al4V alloy surface and its characterizations were detected by Vickers hardness tester,profilometer,scanning electric microscope(SEM),energy dispersive X-ray spectrometer(EDX)and X-ray diffractometer(XRD).Fretting wear behaviors of the coating and its substrate were comparatively tested without lubrication under varied displacement amplitudes(D)in a range of 3-40μm,constant normal load(Fn)of 300 N and frequency of 5 Hz.The results showed that the MAO coating,presenting rough and porous surface and high hardness,mainly consisted of rutile and anatase TiO2 phases.Compared with the substrate,the MAO coating could shift the mixed fretting regime(MFR)and slip regime(SR)to a direction of smaller displacement amplitude.In the partial slip regime(PSR),lower friction coefficients and slight damage appeared due to the coordination of elastic deformation of contact zones.In the MFR,the friction coefficient of the coating was lower than that of the substrate as a result of the prevention of plastic deformation by the hard ceramic surface.With the increase of the displacement amplitude,the degradation of the MAO coating and the substrate increased extremely.The fretting wear mechanisms of the coating were abrasive wear and delamination with some material transfer of specimen.In addition,the coating presented a better property for alleviating fretting wear.
文摘Samples with two different shapes of 2024 aluminum alloy were treated with micro-arc oxidation (MAO), and the formation process and mechanism of oxidation film was analyzed. The results show that different geometrical curvature of the material has an influence upon the uniformity of films and the corrosion-resistance.
文摘Firstly, an aluminum coating was produced metallurgically on mild steel by hot-dipping, then an aluminum oxide coating was formed self-growingly from the aluminum coating by micro-arc oxidation treatment. The structures of the composite coatings were investigated by means of SEM, TEM and XRD. The results show that the composite coating consists of three layers which are Fe-Al alloy, aluminum coating and aluminum oxide orderly outward from the steel substrate. There are amorphous phases, k-Al2O3 and θ-Al2O3 mainly in the aluminum oxide.
基金supported by the Innovation Fund of Huazhong University of Science and Technology,Wuhan,P.R. China (No.2011JC018)
文摘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.
基金This work was finicially supported by the National Natural Science Foundation of China(Grant No.50171026).
文摘Ceramic coatings were prepared on Ti-6AI-4V alloy using ac micro-arc oxidation (MAO) in silicate-hypophosphate solution. Growth regularity and formation mechanism of ceramic coatings were discussed. It was found that during the first stage the growth rate of coatings toward the external surface was larger than that toward substrate and then the coating began to grow mainly towards Ti alloy. When the total coating thickness reaches a certain value, it would no longer increase. In addition, the variations of the composition and microstructure of ceramic coatings according to the depositing time were also investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM).The amount of rutile TiO2 gradually increased, whereas the amounts of the anatase TiO2 and amorphous phases first increased and then decreased slightly.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Key Laboratory of Advanced Welding Technology of Jiangsu Province, China (No. JSAWT-11)
文摘Micro-arc oxidation(MAO)process was carried out in an optimized dual electrolyte system to fabricate a compact,smooth,and corrosion resistant coating on ZK60 Mg alloy.The microstructural characteristics of coating were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).Test of mass loss was conducted at a 3.5%NaCl solution to assess the resistance to corrosion.The bonding strength between the coating and ZK60 substrate was evaluated using scratch experiment.The results reveal that MgAl2O4and MgO are the main phases of ceramic coating obtained in the dual electrolyte system.The corrosion rate of coating prepared in the optimized dual electrolyte is only 0.0061 gám-2áh-1,which demonstrates excellent corrosion resistance.This is mainly due to the compact,uniform coating with high bonding strength.
基金financially supported by the National University Student Innovation Program (No. 101011202)
文摘A ceramic layer was prepared on the surface of Al2O3f /ZL109 composites by means of micro-arc oxidation (MAO) technique. The surface morphology and phase constituent of the ceramic layer were analyzed using scanning electron microscope and X-ray diffraction. The polarization curves of the composites before and after MAO treatment were measured and analyzed. The results showed that after Al2O3f /ZL109 composites were treated using MAO technique in silicate solution, the ceramic layer formed, and it was composed of Al, Si, and mullite phase. Al and Si came from Al alloy matrix of the composites, and the mullite phase formed in process of MAO. Al2O3 fiber in the composites affects the electric conductivity of the composites, the MAO reaction is promoted, and the ceramic layer forming on the composite material side is slightly thicker than that on the Al alloy side. After Al2O3f /ZL109 composites were treated using MAO technique, the corro- sion resistance of the composites is significantly improved.
基金Project(2006KG03) supported by the Science and Technology Program of Shannxi Province, China
文摘Ceramic coating was deposited on TiAl alloy substrate by micro-arc oxidation(MAO)in a silicate-aluminate electrolyte solution with additives including sodium citrate,graphite and sodium tungstate.The microstructures and compositions were analyzed by SEM,EDX and XRD.The corrosion and wear properties of the coatings were investigated by potentiodynamic polarization and ball-on-disc wear test,respectively.The results show that the MAO coatings consist of WO3,Ti2O3,graphite and Al2O3 besides Al2TiO5 and Al2SiO5.With additives in the electrolyte,the working voltage at the micro-arc discharge stage decreases,and the ceramic coating gets smoother and more compact.The corrosion current density of MAO coating is much lower than that of TiAl substrate.It can be reduced from 9.81×10-8A/cm 2to 3.02×10-10A/cm 2 .The MAO coatings composed of hard Al2O3,WO3 and Ti2O3 obviously improve the wear resistance of TiAl alloy.The wear rate is-3.27×10-7g/(N·m).
基金This work was financially supported by the National Natural Science Foundation of China (No. 50171026) and the State Key Laboratory of Tribology, Tsinghua University (No. SKLT04-08)
文摘In the NaAlO2-Na2SiO3 compound system, the ceramic coatings were prepared on magnesium alloy by mi-cro-arc oxidation. The morphology, phase composition, and thermal shock resistance of the ceramic coatings were studied by scanning electron microscope, X-ray diffraction and thermal shock tests, respectively. The results showed that the ce-ramic coating contains MgO, MgAl2O4, as well as a little amount of Mg2SiO4. The thickness of the ceramic coatings in-creases with the current density increasing, when the current density is 12 A?dm?2, the thermal shock resistance of the produced ceramic coating is the best. The hardness of the ceramic coating is up to 10 GPa or so.
基金supported by National Natural Science Foundation of China(Grant No.51171167)Hebei Provincial Natural Science Foundation of China(Grant No.A2011203068)
文摘Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses.However,residual stresses in the surface coatings of structural components have adverse effects on their properties,such as fatigue life,dimensional stability and corrosion resistance,etc.The micro-arc oxidation ceramic coatings are produced on the surfaces of6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW.A constant current density of4.4 0.1 A/dm2and a self-regulated composite electrolyte are used.The micro-arc oxidation treatment period ranges from 10 min to 40min,and the thickness of the ceramic coatings is more than 20μm.Residual stresses attributed toγ-Al2O3constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2ψmethod.The analysis results show that the residual stress in the ceramic coatings is compressive in nature,and it increases first and then decreases with micro-arc oxidation time increase.The maximum stress value is 1667±20 MPa for period of 20 min.Through analyzing the coating thickness,surface morphology and phase composition,it is found that the residual stress in the ceramic coatings is linked closely with the coating growth,the phase composition and the micro cracks formed.It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress.The heat treatment makes the residual compressive stress value decrease 1 378 MPa.The ultrasonic action even alters the nature of the residual stress,making the residual compressive stress change into a residual tensile stress.
基金This work is financially supported by the National Natural Science Foundation of China (Nos. 50572029 and 50272021)the Natural Science Foundation of Guangdong Province, China (No. 0425786).
文摘微弧的氧化(毛) 是在电解质媒介的提高的化学工艺在阀门金属表面上获得涂层结构。毛在磷酸钠电解质获得的三氧化钛电影被调查。这些电影主要由在锐钛矿和金红石形式的 TiO_2 阶段组成并且在表面与 Na 和 P 元素充实。他们的导致磷灰石的能力在模仿的身体液体(SBF ) 被评估。在为超过 30 d 的 SBF 的 Whenimmersing，优先的 carbonated-hydroxyapatite 在这些电影的表面上被形成，它建议对待 MAO 的钛有有希望的积极生物回答。
