镁合金微弧氧化过程中不同电压下获得膜层的性能研究

采用扫描电镜、电化学阻抗方法,研究了镁合金AZ91D微弧氧化过程中不同电压下获得氧化膜的性能.结果表明,随着氧化电压的升高,可以获得三种不同性能的氧化膜:钝化膜、微火花氧化膜和弧光氧化膜.钝化膜很薄,厚度不足1μm,膜层的阻抗随着氧化电压升高略有增加,仍属于钝化膜性质;微火花放电后期得到的膜层较厚,厚度可达30μm,表面均匀、结构致密,具有最高的阻抗,可以达到8×107Ω;弧光放电阶段氧化膜最厚,但结构疏松、易碎,阻抗逐渐降低至1×107Ω.结果还指出,硅酸盐体系中微火花放电阶段后期形成的膜层具有最佳的性能;而且膜层的阻抗主要由氧化膜的有效厚度决定,与总厚度关系不大.     

自组装硅烷膜对 6061 铝合金表面耐蚀性影响的研究

采用自组装方法,在6061铝合金表面制备十二氟庚基丙基三甲氧基硅烷自组装膜层,对制备工艺进行了优化,并对自组装膜层进行了表面形貌分析,通过极化曲线和电化学阻抗谱研究了自组装膜层的耐蚀性能。结果表明:与铝合金基体相比,自组装膜的腐蚀电流密度减小了3个数量级,电化学阻抗值增大了近1倍,达到了提高铝合金表面耐蚀性能的目的。     

镁合金黑色微弧氧化膜在NaCl溶液中腐蚀电化学演变

目的 评价镁合金黑色微弧氧化热控膜层在氯离子作用下的腐蚀演变行为.方法 在电解液中添加不同浓度的添加剂制备微弧氧化膜层,分析不同微弧氧化膜试样在0.1 mol/L NaCl溶液中的电化学演变过程.采用电化学极化、电化学交流阻抗表征和拟合,结合扫描电镜等方法,对膜层演变规律及机理进行了探讨.结果 未经微弧氧化的镁合金自腐蚀电流密度为17.7 μA/cm2,自腐蚀电位为-1.464 V;经微弧氧化后,试样自腐蚀电流密度减小至0.09 μA/cm2,自腐蚀电位下降至-1.628 V.添加剂加入后制备的微弧氧化膜相比于镁合金基体,其耐蚀性能提高,且随着添加剂浓度的增加,耐蚀效果呈现先增加、后减弱的趋势,添加剂质量浓度在10 g/L时制备的膜层具有最好的防腐效果.镁合金微弧氧化热控膜层在NaCl溶液中腐蚀过程分为三个阶段:一是腐蚀性离子进入多孔膜层,引起界面熔融层变化;二是MgO与水分子反应造成内层膜更加致密,阻抗有所增加;三是腐蚀溶液接触到部分镁合金基底,发生电化学腐蚀,形成楔形效应,引发裂纹,最终导致局部腐蚀失效.结论 微弧氧化提高了膜层的耐蚀性能,其在0.1 mol/L NaCl溶液中的腐蚀过程可分为介质进入孔内、水合反应和局部腐蚀三个阶段.     

ZL303铝合金表面微弧氧化陶瓷膜的微结构和耐蚀性研究

为提高ZL303铝合金耐蚀性能,采用微弧氧化技术在ZL303铝合金表面制备陶瓷质氧化膜。通过扫描电镜观察了微弧氧化膜层表面及截面的微结构。利用X射线衍射仪分析了膜层的物相组成。采用腐蚀电化学和高温浸泡实验测试了微弧氧化膜层的耐蚀性。结果表明:所制备的膜层厚度约为13μm,主要由α-Al_2O_3和γ-Al_2O_3组成,外表面存在大量微米级等离子放电微孔。经微弧氧化处理后,试样的电化学阻抗半径增大,自腐蚀电位上升,腐蚀电流密度减小。在高温腐蚀环境中,微弧氧化膜层能有效阻挡腐蚀介质对铝合金基体的侵蚀破坏,耐蚀性能得到提高。     

镁合金抑弧氧化膜层的结构及性能研究

目的了解镁合金抑弧氧化膜层的结构、成分及性能。方法在含有机胺的碱性电解液中,对AZ80镁合金进行抑弧氧化,采用扫描电子显微镜分析、X射线能谱分析、电化学极化曲线测试、摩擦磨损实验等手段测定氧化膜层的结构组成及耐蚀、耐磨性能。结果镁合金抑弧氧化膜层呈双层结构,表层疏松多孔,底层致密。疏松层的摩擦系数在0.2以下,致密层的摩擦系数约为0.8。镁合金经抑弧氧化处理后,腐蚀电位比氧化前仅略有降低,但腐蚀电流密度降低显著。结论抑弧氧化膜降低了镁合金材料的腐蚀速率,提高了其耐蚀、耐磨性能。     

电解质对AZ91D镁合金微弧氧化的影响

在Na2SiO3和NaAlO2为主成膜剂的硅铝复合电解液中,利用交流脉冲电源对AZ91D镁合金进行微弧氧化处理,研究主成膜剂含量的变化对微弧氧化过程及膜层特性的影响规律。利用扫描电镜(SEM)和膜层测厚仪分别研究了膜层的微观形貌和膜层厚度,通过电化学阻抗谱(EIS)测试膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,随着主成膜剂含量的增加,微弧氧化过程中起弧电压和终止电压均呈下降的变化趋势,而膜层耐蚀性则基本呈先增大后降低的变化趋势,膜厚的变化趋势与其耐蚀性一致;Na2SiO3含量的变化对膜层内部致密层和外部疏松层的耐蚀性均有影响,而NaAlO2含量的变化则主要影响膜层内部致密层的耐蚀性;适量的主成膜剂含量是获得致密耐蚀膜层的关键。     

TA2纯钛H3PO4溶液阳极氧化着色膜的表征和电化学分析

利用恒压控制阳极氧化法在H3PO4溶液中于TA2纯钛表面制备了不同颜色的氧化膜,利用扫描电镜、X射线能谱仪、X射线衍射仪、X射线光电子能谱仪分析了着色膜的形貌、成分、物相和价态,使用电化学工作站在Hank’s模拟体液中研究了着色膜的Tafel极化曲线和电化学阻抗谱(EIS)。结果表明:SEM显示着色膜由一层表面多孔、内层致密的膜层构成;EMAX显示膜层由单一的Ti和O元素构成;XRD和XPS显示膜层主要由Ti4+和O2-组成,呈非晶态TiO2结构;Tafel极化曲线显示随着电压升高,着色膜腐蚀电位正移、腐蚀电流密度下降;EIS显示随着电压升高,着色膜容抗弧半径增大、阻抗值增加,耐腐蚀性提高。     

有机胺对镁合金阳极氧化的影响

以NH4H2PO4、NaF和NaOH组成基础电解液, 采用有机胺作为抑弧剂, 对AZ91D镁合金高压阳极氧化过程进行了研究.结果表明: 有机胺对镁合金的阳极氧化有着显著的抑弧效应, 可使镁合金的阳极火花放电电压提高50～80V.在抑制阳极发生弧光放电的状态下, 镁合金表面可以沉积一层致密、具有较高硬度和优良耐蚀性能的氧化膜层.分析了有机胺对氧化膜层性能和表面形貌的影响以及不同有机胺在镁合金阳极氧化过程中的抑弧能力, 并初步探讨了有机胺在镁合金阳极氧化过程中的抑弧机理.     

纳米SiC对AZ91D镁合金微弧氧化膜微观结构及性能的影响（英文）

通过向Na2Si O3-Na Al O2复合电解液体系中添加纳米Si C,经过微弧氧化处理后在AZ91D镁合金表面制备含纳米SiC的复合陶瓷层。利用SEM、膜层测厚仪、XRD、EDS和维氏硬度计分别研究膜层的微观形貌、厚度、相结构、元素组成及硬度。采用摩擦磨损试验机对镁合金基体和膜层的干滑动磨损行为进行研究,运用动电位极化曲线试验和交流阻抗法测量镁合金基体和膜层在3.5%Na Cl溶液中的耐蚀性能。结果表明:向电解液中添加纳米Si C后,微弧氧化的起弧电压和终止电压均下降。经纳米SiC复合处理后,微弧氧化膜层的孔径减小,致密性提高;与未添加纳米Si C的膜层相比,其厚度和硬度都得到提升,耐磨性与耐蚀性均增强。     

氧化时间对2024铝合金表面微弧氧化涂层组织与耐蚀性的影响

采用铝酸盐为主的碱性电解液,在2024铝合金表面制备微弧氧化涂层。通过表面形貌、涂层厚度与生长速率,研究了氧化时间对涂层结构的影响;通过动电位极化曲线及电化学阻抗谱研究了微弧氧化涂层在NaCl溶液中的腐蚀行为。结果表明:微弧氧化涂层表面形成了许多大小不一的微孔,表面的陶瓷颗粒以搭桥的方式在表面不同部位堆积。随着氧化时间的延长,该微弧氧化涂层的厚度逐渐增大,生长速率减慢;经过不同氧化时间的处理,与铝合金基体相比,涂层的腐蚀电压升高,腐蚀电流密度有不同程度的减小;氧化时间20 min的微弧氧化涂层的腐蚀电流密度低、腐蚀电压高,膜层的耐蚀性能较好。     

负向电压对海洋平台铝合金钻探管表面微弧氧化膜组织和耐蚀性影响

目的 提高海洋平台铝合金钻探管的耐腐蚀性能.方法 采用微弧氧化技术,在海洋平台钻探管用2 A12铝合金表面制备氧化铝陶瓷膜.通过盐雾试验,研究负向电压对微弧氧化膜耐腐蚀性的影响,并通过扫描电子显微镜和光学显微镜对微弧氧化膜的微观形貌、组织结构进行分析.结果 在微弧氧化处理过程中,随着负电压的升高,微弧氧化膜表面的孔径先增大后减小,膜表面变光滑.在一定负电压范围内,Al2 O3相的含量随负电压的升高先增加,当负电压达到一极限值后,Al2 O3相随负电压的升高而减少.负电压的增大能提高微弧氧化膜的耐腐蚀性,当负电压由8 V升高至24 V时,腐蚀速率由0.00568 g/(dm2·h)降低至0.00028 g/(dm2·h),前者是后者的20倍;当负电压为4 V时,部分膜层剥落,腐蚀严重;当负电压增至24 V时,有效延缓了微弧氧化膜的腐蚀程度.结论 在微弧氧化处理过程中,负电压对微弧氧化膜的制备有较大影响,增大负电压能有效提高微弧氧化膜的耐腐蚀性,此外基体本身所含的Fe、S等杂质是影响微弧氧化膜的主要因素.     

Growth mechanism and corrosion behavior of ceramic coatings on aluminum produced by autocontrol AC pulse PEO

Ceramic coatings are produced on aluminum alloy by autocontrol AC pulse Plasma Electrolytic Oxidation (PEO) with stabilized average current. Transient signal gathering system is used to study the current, voltage, and the transient wave during the PEO process. SEM, OM, XRD and EDS are used to study the coatings evolution of morphologies, composition and structure. TEM is used to study the micro profile of the outer looser layer and inner compact layer. Polarization test is used to study the corrosion property of PEO coatings in NaCl solution. According to the test results, AC pulse PEO process can be divided into four stages with different aspects of discharge phenomena, voltage and current. The growth mechanism of AC PEO coating is characterized as anodic reaction and discharge sintering effect. PEO coating can increase the corrosion resistance of aluminum alloy by one order or two; however, too long process time is not necessarily needed to increase the corrosion resistance. In condition of this paper, PEO coating at 60 min is the most protective coating for aluminum alloy substrate.     

Influence of sodium silicate concentration on properties of micro arc oxidation coatings formed on AZ91HP magnesium alloys

In a base solution containing 10 g/L sodium hydroxide and 12 g/L phytic acid, the influence of sodium silicate concentration on the formation and properties of anodic coatings obtained by micro arc oxidation (MAO) on magnesium alloys was systematically studied. The results demonstrate that sodium silicate can increase the solution conductivity, decrease the final voltage and change the coating color. Amorphous magnesium silicate is detected and the silicon content in the coatings continually increases with the increasing of sodium silicate concentration. Silicate ions can simultaneously combine with magnesium and aluminum ions to develop anodic coatings, while phytic acid radicals preferentially react with magnesium ions. Sodium silicate can further improve the corrosion resistance of MAO treated magnesium and the coating shows the best corrosion resistance in the base solution with 10 g/L sodium silicate.     

Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro‐arc oxidization technique

With increasing applied voltage, three types of anodic coatings, passive film, micro‐spark ceramic coating and spark ceramic coating were made by micro‐arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali‐silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro‐spark ceramic coating, prepared in the voltage range of 170~220V exhibits compact, homogeneous structure and highest corrosion‐resistance.     

基于Ti-5Al-1V-1SN-1Zr-0.8Mo合金的分段电压微弧氧化膜层的研究

本文主要研究分段电压对于钛合金表面所制备的微弧氧化膜层特性的影响。利用扫描电子显微镜(SEM)和激光扫描共聚焦显微镜对MAO膜层的结构进行了表征,利用能谱分析(EDS)和X射线衍射(XRD)并对膜层成分进行分析。对比评价了不同分段电压模式下膜层的厚度、粗糙度和耐蚀性。结果表明,与不同分段电压相比,第一阶段电压为320V 氧化时间180s与第二阶段电压为420V氧化时间为720s,所形成的膜层粗糙度最小。第一阶段外加电压320V氧化时间120s与第二阶段外加电压420V时间780s,膜层最为致密,耐腐蚀性最好。XRD结果表明,膜层是由TiO2和亚稳态Ti2O3组成。     

环氧粉末涂层的冲蚀性能及其与固化度之间的关系

利用旋转圆盘式冲刷腐蚀试验装置,研究了不同固化度的ＳＥＢＦ－２型熔融结合环氧粉末涂层在１％ＮａＣｌ＋１％金刚砂砂浆中的冲蚀特性,并观察了涂层表面形貌,实验结果表明：对不同条件固化的试样,固化度越高,抗冲蚀性能越好,因化度相同而固化工艺不同时,涂层的冲蚀性能存在一定的差异,高温短时间固化涂层不如低 长时间固化涂层耐冲蚀,这与其交联结构密切相关。     

Effects of electric parameters on corrosion resistance of anodic coatings formed on magnesium alloys

Anodic coatings were obtained by micro-arc oxidation on AZ91HP magnesium alloys in a solution containing 10 g/L NaOH and 8 g/L phytic acid. The effects of electric parameters including frequency, final voltage, duty cycle and current density on the corrosion resistance of anodic coatings formed on the magnesium alloys were investigated by using an orthogonal experiment of four factors with three levels. The results show that the final voltage plays a main role on the coating properties. The orders of affecting corrosion resistance and coating thickness are separately ranked from high to low as, final voltage>duty cycle>current density>frequency and final voltage>current density>frequency>duty cycle. The final voltage influences the corrosion resistance of the anodized samples mainly by changing the surface morphology and coating thickness.     

Hot erosion wear and carburization in petrochemical furnaces

High temperature alloy stainless steels used in olefins manufacturing furnaces are exposed to extreme environmental degradation processes inclusive of carburization, oxidation and hot erosion wear. A study was undertaken to understand the hot erosion wear phenomenon in relation to substrate composition, atmosphere, temperature, time and the influence of carburization. An erosion wear test rig was designed and constructed to simulate the wear degradation process up to 1200°C. Results have shown a surprising relationship between erosion wear rate and temperature for the most prominent stainless steel alloy used in the industry. A novel coating technology was developed for mitigation that enables the non‐line‐of‐sight application of protective macro‐coatings typically 1 to 5 mm in thickness. Stainless steel coupons treated with these macro‐coatings have exhibited an enhanced resistance to both oxidation and carburization. These macro‐coatings also provide superior hot erosion wear resistance as compared to the uncoated stainless steel. A thorough examination of the microstructure and micro‐mechanical properties of the coatings is presented. Targeted applications include petrochemical furnace fittings (return bends), thermo‐wells and transfer‐line‐exchanger (TLE) surfaces. Commercial furnace trials of the prototype products have been initiated with some prototypes in field trials for over 18 months. Results of both laboratory accelerated testing and field evaluation will be discussed.     

The influence of sodium tungstate concentration and anodizing conditions on microarc oxidation (MAO) coatings for aluminum alloy

Microarc oxidation (MAO) coatings on 5052 aluminum alloy are prepared in silicate–hypophosphite electrolytes with sodium tungstate. The effects of sodium tungstate concentrations and current density on the surface morphology, phase composition and properties of the coatings are investigated. With the addition of sodium tungstate in the electrolyte and increase of current density, the final voltage at the microarc discharge process increases. The results also show that the MAO coatings are composed mainly of α-Al₂O₃ and γ-Al₂O₃ and the proportion of α-Al₂O₃ and γ-Al₂O₃, pore size, surface roughness as well as thickness of the coatings strongly depend on the sodium tungstate concentration and current density. Thus, the hardness, friction coefficient and corrosion resistance of the coatings are significantly influenced by the magnitude of the current density and sodium tungstate concentration. These oxide films on aluminum were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thickness gage, and polarization curves, respectively.     

Oxide scales formation in nano-crystalline TiAlCrSiYN PVD coatings at elevated temperature

Nano-crystalline TiAlCrSiYN plasma vapor deposited (PVD) coatings were developed for oxidation and wear protection at elevated temperatures. Compositional tuning of the coatings was performed to enhance oxidation protection at elevated temperatures.The oxidation kinetics of the coatings has been studied over 180 h at 900 °C in air. Post-oxidation microstructural examinations of specimens were performed using transmission electron microscopy (TEM), secondary electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and glow discharge optical emission spectroscopy (GDOES). Micro mechanical characteristics of the coating were studied using a micro materials nanotest system. Wear resistance of the coatings were studied during turning of Inconel 718.Experimental results clearly indicate that the aluminum-rich PVD TiAlCrSiYN coatings with 60 at.% of Al can improve oxidation resistance of titanium aluminide alloy at the temperature 900 °C as well as wear resistance during machining of Inconel 718. It was shown that during oxidation, continuous protective alumina-based oxide films form on the surface. These oxides are predominantly (Al,Cr)₂O₃-based films. Self-healing behavior of the TiAlCrSiYN coatings was observed in its ultra-fine nano-crystalline structure.