Microarc oxidation coating fabricated on AZ91D Mg alloy in an optimized dual electrolyte

Microarc oxidation （MAO） process was conducted on AZ91D magnesium alloy in an electrolyte composed of NazSiO3, NaAlO2, NaEB4O7, NaOH, C3H803 and C6H5Na307 by AC pulse electrical source. The surface and cross-sectional morphologies, film thickness, chemical composition and structure of the coatings were characterized by scanning electron microscopy（SEM）, layer thickness metry, energy disperse spectroscopy（EDS） and X-ray diffraction（XRD）. The corrosiofi resistances of the coatings in a 3.5% NaC1 neutral solution were evaluated by electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization test. The results showed that an optimized electrolyte with a composition of 15 g/L NazSiO3, 9 g/L NaA102, 2 g/L NazB407, 3 g/L NaOH, 5 mL/L C3H803 and 7 g/LC,HsNa307 was developed by means of orthogonal experiment. The coating obtained in the optimized electrolyte had a dense structure and revealed a lower current density, decreased by two orders of magnitude as compared with the magnesium substrate. Meanwhile, the corrosive potentials of the coated samples increased nearly by 73 inV. EIS result showed that the corrosion resistance of the coating was mainly determined by the inner dense layer. The coating primarily contained elements Mg, Al, O and Si and XRD analyses indicated that the coating was mainly composed of MgO, Mg2SiO4 and MgAl204.

Influence of Electrolytes on the Microstructure of Microarc Oxidation Coatings on Ti-6Al-4V Alloy

Dense ceramic oxide coatings of about 50 μm may be prepared on Ti-6AI-4V alloy surface by alternating-current microarc oxidation in aluminate and silicate solutions, respectively. Their phase constituent and microstructure were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the electrolytic ions have incorporated into the interior of the coatings. The coating formed in aluminate solution is composed of the rutile TiO2 and TiAl2O5 phases rather than the rutile, anatase and amorphous SiO2 phases for the coating formed in silicate solution. However, TiAl2O5 content in the outer layer of the two coatings is much higher than in the inner layer. It is suggested that all these oxides may result from a rapid solidification of the molten coating in the microarc discharge zone.

Influence of anions in phosphate and tetraborate electrolytes on growth kinetics of microarc oxidation coatings on Ti6Al4V alloy

The growth kinetics of microarc oxidation(MAO)coatings on Ti6Al4V alloy was studied by designing an electrolyte with low PO_(4)^(3−)content and high B_(4)O_(7)^(2−)content,using scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and potentiodynamic polarization.The results showed that B_(4)O_(7)^(2−)increased the spark intensity and dissolved most of the oxides at high temperatures.Then,a thicker barrier layer at the coating/substrate interface was produced,which increased the polarization resistance of the coating.PO_(4)^(3−)at a low concentration also promoted the uniform growth of the MAO coating and the formation of hat-shaped holes in the outer deposition layer.The thickness of the MAO coatings obtained in Na_(2)B_(4)O_(7) electrolytes exhibited an exponential increase with time at spark discharge stage,while that of the MAO coating obtained in phosphate–tetraborate electrolytes showed a linear trend as the PO_(4)^(3−)content increased.

Growth kinetics and mechanism of microarc oxidation coating on Ti-6Al-4V alloy in phosphate/silicate electrolyte

Microarc oxidation(MAO)is an effective surface treatment method for Ti alloys to allow their application in extreme environments.Here,binary electrolytes consisting of different amounts of sodium phosphate and sodium silicate were designed for MAO.The surface morphology,composition,and properties of MAO coatings on Ti-6Al-4V alloy treated in 0.10 mol/L electrolyte were investigated to reveal the effect of PO_(4)^(3-)and SiO_(3)^(2-)ray diffraction,and potentiodynamic polarization.The results showed that PO_(4)^(3-)is beneficial for generating microarcs and forming pores within the coating,resulting in a thick but porous coating.SiO_(3)^(2-)eration of microarcs,resulting in a thin dense coating.The thickness,density,phases content,and polarization resistance of the MAO coatings are primarily affected by the intensity of microarcs for low SiO_(3)^(2-)ciently high.The thickness of MAO coatings obtained in P/Si electrolytes shows a piecewise linear increase with increasing process time during the three stages of microarc discharge.SiO_(3)^(2-)discharge,but slows down the growth of the coating formed in the next stage.

Electrochemical performance of microarc oxidation films formed on AZ91D alloy in two group electrolytes

The phase composition and electrochemical performances of microarc oxidation（MAO） films prepared on AZ91D alloy by using step-down current method in a phosphate electrolyte（P-film） and silicate electrolyte（Si-film） were studied. The results show that P-film is mainly composed of Mg, MgAl2O4 and MgO, and Si-film is composed of Mg2SiO4 and MgO. There clearly exists a fluoride-enriched zone with the thickness of about 12μm for P-film and 0.71μm for Si-film at the MAO coating/substrate interface. The electrochemical tests show that both P-film and Si-film can enhance the corrosion resistance of AZ91D magnesium alloy significantly. The corrosion failure process of the two films in 5%（mass fraction） NaCl solution is quite different.

Electrolyte Optimization of Microarc Oxidation of Magnesium Alloy

Magnesium alloy AZ91D was processed respectively in one, two, three and four-component electrolytes by using AC microarc oxidation technique. The corrosion resistance of AZ91D alloy was measured by electrochemical methods. The optimum electrolytes in two, three and four components were found. In four-component electrolyte composed by NaOH, NaAlOj, H2O2 and C4H4O6N32, the film formed on AZ91D alloy is smooth and compact, and has a higher corrosion resistance. The effect of the ingredients in electrolytes was discussed based on their roles in the formation of corrosion resistant film.

Plasma electrolytic oxidation of the magnesium alloy MA8 in electrolytes containing TiN nanoparticles

The formation of protective multifunctional coatings on magnesium alloy MA8 using plasma electrolyt- ic oxidation （PEO） in an electrolytic system containing nanosized particles of titanium nitride was investigated. Electrochemical and mechanical properties of the obtained layers were examined. It was established that microhardness of the coating with the nanoparticle concentration of 3 gl-1 increased twofold （4.2 ± 0.5 GPa）, while wear resistance decreased （4.97 × 10-6 mm3 N-1 m-1）, as compared to re- spective values for the PEO-coating formed in the electrolyte without nanoparticles （2.1 ± 0.3 GPa, 1.12 × 10.5 mm3 N-1 m-1）.

Corrosion and wear resistance of coatings produced on AZ31 Mg alloy by plasma electrolytic oxidation in silicate-based K2TiF6 containing solution:Effect of waveform

In this research,plasma electrolytic oxidation coatings were prepared on AZ31 Mg alloy in a silicate-based solution containing K_(2)TiF_(6) using bipolar and soft sparking waveforms with 10,20,and 30%cathodic duty cycles.The coatings displayed a net-like surface morphology consisted of irregular micro-pores,micro-cracks,fused oxide particles,and a sintered structure.Due to the incorporation of TiO_(2) colloidal particles and the cathodic pulse repair effect,most of the micro-pores were sealed.Long-term corrosion performance of the coatings was investigated using electrochemical impedance spectroscopy during immersion in 3.5 wt.%NaCl solution up to 14 days.The coating grown by the soft sparking waveform with a 20%cathodic duty cycle having the lowest porosity(6.2%)and a sharp layer concentrated in F element at the substrate/coating interface shows the highest corrosion resistance.The friction coefficient of this coating has remained stable during the sliding even under 5 N normal load,showing relatively higher wear resistance than other coatings.The coating produced using the equivalent unipolar waveform,as the reference specimen,showed the highest friction coefficient and the lowest wear resistance despite its highest micro-hardness.

纳米镍颗粒改性钛合金微弧氧化膜的摩擦性能

目的基于微弧成膜机制形成的类陶瓷氧化膜层中存在大量孔洞、裂纹和凸起,使得膜层的致密性和耐磨性不够理想。通过在钛合金微弧氧化膜中引入镍,从而改善膜层的组织结构,提高膜层的抗磨性能。方法利用不同含量纳米镍颗粒的碱性电解液,在TC4钛合金表面制备微弧氧化膜层。利用SEM、EDS、XRD、XPS对微弧氧化膜层的微观结构、截面形貌、相组成和元素组成进行分析,采用显微维氏硬度计和摩擦磨损试验机检测膜层的硬度和摩擦学性能。结果纳米镍颗粒的引入,使得微弧氧化膜的厚度增加,提高了膜层的致密性。当纳米镍颗粒的加入量(质量浓度)为2 g/L,且微弧氧化时间为45 min时,膜层表面微孔分布均匀,凸起和微裂纹较少。微弧氧化膜主要由金红石相和锐钛矿相组成,进入膜层的Ni主要以NiO的形式存在。在添加2 g/L纳米镍颗粒、微弧氧化时间为45 min时,制备的膜层硬度为452HV,抗磨性能表现最好,其摩擦因数一直稳定在0.75左右,抗磨性能相较于基础膜层提升了约67%。结论适当加入纳米镍颗粒及采用合理的微弧氧化时间能够减少膜层的微孔和微裂纹,进一步提高膜层的硬度和抗磨性能。

添加ZrO_(2)的钛合金微弧氧化膜表面微结构及性能研究

针对钛合金硬度低和表面摩擦性能差等问题,在Na_(2)SiO_(3)-Na_(3)PO_(4)-NaAlO_(2)中添加ZrO_(2),用微弧氧化技术在TC4钛合金表面制备高硬耐磨复合膜层。研究电压、氧化时间、ZrO_(2)添加量对膜层表面形貌和组成的影响,研究复合膜层的硬度和摩擦因数变化规律。结果表明:ZrO_(2)颗粒主要分布于膜层表面,少许进入孔洞中。电压、氧化时间及ZrO_(2)添加量对复合膜层表面微结构有显著影响。均匀分散在膜表面的ZrO_(2)颗粒、形成的ZrTiO_(4)相及膜表面平整度的共同作用,改善钛合金微弧氧化膜层硬度与摩擦性能。

钛合金微弧氧化涂层的高温性能研究

钛合金的低密度、高比强度和良好的耐腐蚀性等优点使其具有广阔的应用前景,但其硬度低、耐磨性差和抗高温氧化性能差等缺点限制了其应用。通过微弧氧化技术在钛合金表面制备出复合陶瓷涂层可有效提高基体的抗高温氧化性能和抗热震性能。同时,对部分涂层进行封孔或掺杂处理,其高温性能更加优异。

A first look at the formation of PEO-PDA coatings on 3D titanium

Additive manufacturing has revolutionized implantology by enabling the fabrication of customized,highly porous implants.Surface modifications using electrochemical methods can significantly enhance the bioactivity and biocompatibility of biomaterials,including 3D-printed implants.This study investigates novel coatings on 3D titanium(Ti)samples.Mesh Ti samples were designed and subjected to plasma electrolytic oxidation(PEO)to form a calcium phosphate coating.Subsequently,a layer of polydopamine(PDA)was applied.The electrochemical properties and morphology of the coatings were analyzed.Scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS)revealed well-developed coatings containing calcium phosphates(including hydroxyapatite),titanium dioxide,and polymerized dopamine,suggesting promising bioactive potential.Composite layers incorporating PDA exhibited superior protective properties compared to base PEO coatings.

Ti-6Al-4V在NaAlO_2溶液中微弧氧化陶瓷膜的组织结构研究

利用交流微弧氧化方法在NaAlO2 溶液中在Ti- 6Al- 4V合金表面制备出氧化物陶瓷膜 ,用扫描电镜及能谱仪研究了陶瓷膜的形貌、组织和Ti、Al、O元素的分布 ,并用X射线衍射分析了陶瓷膜的相组成 .所制备的陶瓷膜与基体界面结合良好 ,膜厚约 5 0微米 ,分为内外两层 .外层膜由大量TiAl2 O5相及少量金红石型TiO2 相组成 .内层膜的TiAl2 O5相含量显著降低 ,金红石则成为主体相 ,同时还发现少量TiO1.9相 .这些相都是由微弧区熔融物快速冷却形成的 .微弧区高温高压过程没有改变膜 /基体界面附近的合金基体组织 .

TC4钛合金表面交流微弧氧化膜研究

在铝酸盐溶液中，采用交流微弧氧化方法在ＴＣ４钛合金表面制备出氧化物陶瓷膜．使用显微力学探针测定了膜的硬度和弹性模量分布，并探讨了微弧放电对氧化膜和钛合金基体组织、性能的影响．结果表明，钛合金表面经微弧氧化处理后，膜／金属界面附近钛合金基体显微组织保持不变，基体上也不存在硬化区．另外，来自溶液氧原子没有扩散进入未氧化的钛合金基体．氧化膜的显微硬度和弹性模量分布有相似的变化规律．从膜表层到膜内部，硬度和弹性模量逐渐增加．靠近钛／膜界面附近时达到最大值。分别为１３和２３０ＧＰａ膜不同深度处ＴｉＯ２金红石和ＴｉＡｌ２Ｏ５尖晶石相的相对含量变化决定了硬度和弹性模量分布．

电参数对Ti6Al4V合金微弧氧化陶瓷膜结构特性的影响

采用交流微弧氧化法于Na_2SiO_3-KOH-(NaPO_3)_6。溶液中在Ti_6A14V表面形成了氧化物陶瓷膜.研究了微弧氧化电压与频率对陶瓷膜的生长速率、组织形貌和相组成的影响.结果表明:随电压的升高或频率的减小,膜层的生长速率增加,膜层的表面质量变得粗糙.相对致密均匀的膜层主要由TiO_2(锐钛矿相及金红石相)相组成,电压与频率电参数影响膜层的相组成,随电压的升高和频率的减小,膜层中锐钛矿相TiO_2的相对含量减小,金红石相TiO_2的相对含量增加,并成为主晶相.

钛合金在硅酸盐溶液中微弧氧化陶瓷膜的组织结构

利用微弧氧化方法在硅酸盐溶液中在Ti6Al4V合金表面生长出一层厚度达50μm的陶瓷氧化膜,并用X射线衍射(XRD)、扫描电镜(SEM)初步研究了氧化膜的组织结构。该氧化膜由大量金红石型TiO2和SiO2非晶相及少量锐钛矿型TiO2相组成,且膜内层金红石含量比膜外层高。这些相都是由微弧区熔融物快速冷却形成的。硅元素已扩散到膜内层,Ti、Si元素在膜内部分布是不均匀的。

磷酸盐系溶液中钛合金微弧氧化涂层生长与组织结构

采用常流脉冲控制方式于(NaPO3)6 NaF NaAlO2溶液中用微弧氧化法在Ti6Al4V表面制备了陶瓷化涂层,研究了涂层的生长过程及组织结构变化。结果表明:氧化过程中涂层的生长经历了由快到慢的过程,在前10min涂层以较快速度生长(约3μm/min),随着时间的延长涂层生长速度逐渐减慢;生长过程中涂层表面微孔数目减少,微孔孔径增大,涂层表面气孔率增大;涂层主要由二氧化钛的两种不同变体(锐钛矿及金红石)以及磷化物相AlPO4组成;随着氧化的进行,锐钛矿含量降低,金红石含量增加,氧化过程中发生了锐钛矿相到金红石相的相转变;结晶AlPO4相是通过水合多聚磷酸铝在放电区附近发生高温热解反应而进入涂层。

微弧氧化-水热合成生物活性二氧化钛层的结构与性能

在钛合金基体上通过微弧氧化形成含钙和磷的二氧化钛层 ,再经过水热合成转化为含羟基磷灰石的生物活性二氧化钛层 ,该膜层结合强度高 ,而且是多孔和均匀的。因此 ,该方法很适合钛合金植入体的生物活性表面改性。

处理电压对钛合金微弧氧化膜相结构的影响

在Na2CO3Na2SiO3溶液中,采用正负不对称的专用交流高压电源制备了钛合金微弧氧化膜.利用X射线衍射研究了处理参数(阴、阳极峰值电压,处理时间等)对微弧氧化膜相结构的影响.实验结果表明,氧化膜主要由金红石和锐钛矿的TiO2及少量不饱和氧化的Ti6O11(TiO1.83)相组成,它们在氧化膜中各自所占的比例受处理时间和阴、阳极峰值电压的影响较大.当阴、阳极峰值电压分别控制在45V和320V,处理时间为30min时,氧化膜中金红石TiO2的含量最高,达到80%.

Ti6Al4V表面微弧氧化陶瓷涂层的结构和摩擦学特性

采用交流微弧氧化法,在Na2SiO3-(NaPO3)6-Na3MoO4溶液中制备了Ti6Al4V表面氧化物陶瓷涂层,用X射线衍射仪、扫描电子显微镜和球-盘摩擦磨损试验机研究了涂层的结构、形貌及摩擦学性能,用纳米压痕仪测定了涂层致密层的硬度,用扫描电子显微镜观察涂层磨损表面形貌,用能谱仪分析涂层磨屑的元素组成.结果表明:厚约20μm的涂层致密均匀,主要由锐钛矿和金红石相氧化钛组成;涂层致密层的硬度约为13.5GPa;在0.5N低载荷和摩擦循环次数小于2000次条件下,涂层同GCr15钢对摩时的摩擦系数仅为0.18～0.20,较基底Ti6Al4V与其对摩的摩擦系数低得多.摩擦过程中较软的GCr15钢球材料向涂层表面转移,涂层的磨损机制主要是轻微磨粒磨损与粘着磨损.