Investigation of anti-corrosion property of hybrid coatings fabricated by combining PEC with MAO on pure magnesium

Novel hybrid coatings on pure magnesium were prepared by combining plasma electrolytic carburizing(PEC)with micro-arc oxidation(MAO)to further enhance the anti-corrosion property in this paper.Scanning electron microscopy(SEM)was used to observe the microstructure of the coatings,meanwhile,energy dispersive spectrometry(EDS)and X-ray diffraction(XRD)were separately used to investigate the elemental as well as phase compositions of the coatings.The anti-corrosion property of the coatings was evaluated by potentiodynamic polarization curves as well as electrochemical impedance spectroscopy(EIS).The results show that PEC process is closely related with the effects of adsorption as well as diffusion of the activated carbon atoms,and it can provide a favorable pretreatment surface with predesigned chemical composition to obtain a new kind of phase,namely Si C with superior corrosion resistance and chemical stability,in the following PEC+MAO hybrid coatings.Meanwhile,PEC preprocessing also can afford an excellent micro-structure to increase the coating thickness as well as to improve the compactness of the PEC+MAO hybrid coatings.During the fabrication process of the PEC+MAO hybrid coatings,an overlapping phenomenon in regard to coating thickness can be observed instead of heaping up layer by layer.Compared with both single PEC surface modification layers as well as single MAO coatings,the PEC+MAO hybrid coatings exhibit more superior anti-corrosion property.Especially,the EIS data reveal that the PEC+MAO hybrid coatings can act as an effective protection system to provide relatively excellent long-range anti-corrosion protection.Note also that employing same MAO technique for both single MAO treatment as well as PEC+MAO combining procedure is the key to this research.

Time-course monitoring of in vitro biotransformation reaction via solid-phase microextraction-ambient mass spectrometry approaches

The solid-phase microextraction technique quantifies analytes without considerably affecting the sample composition.Herein,a proof-of-concept study was conducted to demonstrate the use of coated probe electrospray ionization(coated-PESI)and coated blade spray(CBS)as ambient mass spectrometry approaches for monitoring drug biotransformation.The ability of these methods was investigated for monitoring the dephosphorylation of a prodrug,combretastatin A4 phosphate(CA4P),into its active form,combretastatin A4(CA4),in a cell culture medium supplemented with fetal bovine serum.The CBS spot analysis was modified to achieve the same extraction efficiency as protein precipitation and obtained results in 7 min.Because coated-PESI performs extraction without consuming any samples,it is the preferred technique in the case of a limited sample volume.Although coated-PESI only extracts small quantities of analytes,it uses the desorption solvent volume of 5-10 pL,resulting in high sensitivity,thus allowing the detection of compounds after only 1 min of extraction.The biotransformation of CA4P into CA4 via phosphatases occurs within the simple matrix,and the proposed sample preparation techniques are suitable for monitoring the biotransformation.

Thermal residual stress analysis of diamond coating on graded cemented carbides

Finite element model was developed to analyze thermal residual stress distribution of diamond coating on graded and homogeneous substrates. Graded cemented carbides were formed by carburizing pretreatment to reduce the cobalt content in the surface layer and improve adhesion of diamond coating. The numerical calculation results show that the surface compressive stress of diamond coating is 950 MPa for graded substrate and l 250 MPa for homogenous substrate, the thermal residual stress decreases by around 24% due to diamond coating. Carburizing pretreatment is good for diamond nucleation rate, and can increase the interface strength between diamond coating and substrate.

Comparison of different approaches for direct coupling of solid-phase microextraction to mass spectrometry for drugs of abuse analysis in plasma

The direct coupling of solid-phase microextraction(SPME)to mass spectrometry(MS)(SPME-MS)has proven to be an effective method for the fast screening and quantitative analysis of compounds in complex matrices such as blood and plasma.In recent years,our lab has developed three novel SPME-MS techniques:SPME-microfluidic open interface-MS(SPME-MOI-MS),coated blade spray-MS(CBS-MS),and SPME-probe electrospray ionization-MS(SPME-PESI-MS).The fast and high-throughput nature of these SPME-MS technologies makes them attractive options for point-of-care analysis and anti-doping testing.However,all these three techniques utilize different SPME geometries and were tested with different MS instruments.Lack of comparative data makes it difficult to determine which of these methodologies is the best option for any given application.This work fills this gap by making a comprehensive comparison of these three technologies with different SPME devices including SPME fibers,CBS blades,and SPME-PESI probes and SPME-liquid chromatography-MS(SPME-LC-MS)for the analysis of drugs of abuse using the same MS instrument.Furthermore,for the first time,we developed different desorption chambers for MOI-MS for coupling with SPME fibers,CBS blades,and SPME-PESI probes,thus illustrating the universality of this approach.In total,eight analytical methods were developed,with the experimental data showing that all the SPME-based methods provided good analytical performance with R^(2)of linearities larger than 0.9925,accuracies between 81%and 118%,and good precision with an RSD%≤13%.

Facile fabrication of novel cobalt-based carbonaceous coatings on nickel-titanium alloy fiber substrate for selective solid-phase microextraction

Fabrication of selective adsorption coatings plays a crucial role in solid-phase microextraction(SPME).Herein,new strategies were developed for the in-situ fabrication of novel cobalt-based carbonaceous coatings on the nickel-titanium alloy(Ni Ti)fiber substrate using ZIF-67 as a precursor and template through the chemical reaction of ZIF-67 with glucose,dopamine(DA)and melamine,respectively.The adsorption performance of the resulting coatings was evaluated using representative aromatic compounds coupled to high-performance liquid chromatography(HPLC)with ultraviolet detection(HPLC-UV).The results clearly demonstrated that the adsorption selectivity was subject to the surface elemental composition of the fiber coatings.The cobalt and nitrogen co-doped carbonaceous coating showed better adsorption selectivity for ultraviolet filters.In contrast,the cobalt-doped carbonaceous coating exhibited higher adsorption selectivity for polycyclic aromatic hydrocarbons.The fabricated fibers present higher mechanical stability and higher adsorption capability for model analytes than the commercial polydimethylsiloxane and polyacrylate fibers.These new strategies will continue to expand the Ni Ti fibers as versatile fiber substrates for metal-organic frameworks(MOFs)-derived coating materials with controllable nanostructures and tunable properties.

HK40钢的渗铝新工艺及抗碳化腐蚀性能研究

采用金相显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线能谱分析仪(EDAX)等仪器设备研究了HK40钢的渗铝及其抗碳化腐蚀能力。试验结果表明,通过调整渗剂中特种添加剂与铝粉的比例和渗铝温度等工艺参数,可达到控制渗铝层相组成的目的。与传统一段法固体粉末渗铝工艺相比,两段法固体粉末渗铝工艺可提高渗速约60％。HK40钢的渗铝层由NiAl相和Ni3Al相组成时,其抗碳化腐蚀能力得到明显提高。

奥氏体不锈钢离子渗碳后的腐蚀行为

为了提高奥氏体不锈钢零件的使用寿命,利用低温离子渗碳技术对AISI316L奥氏体不锈钢进行了表面渗碳处理。用X射线衍射仪和光学显微镜分析了渗碳层的微观组织结构,用显微硬度计测试了渗碳层的硬度分布,通过电化学极化曲线测试技术和化学腐蚀试验研究了离子渗碳AISI316L不锈钢的腐蚀行为。渗碳层为单相碳过饱和奥氏体固溶体,由此明显提高了AISI316L不锈钢的抗腐蚀性能,渗碳层硬度梯度平缓,表面显微硬度高达900HV。结果表明,奥氏体不锈钢低温离子渗碳处理不仅提高了其表面硬度,而且提高了不锈钢表面的耐腐蚀性能,从而提高了其使用寿命。

呋喃树脂砂用防渗碳涂料的试验研究

介绍了低碳、超低碳不锈钢铸件呋喃树脂砂用防渗碳涂料的防渗碳原理、涂料的主要成分、性能影响因素.中试试验结果表明,高渗透活性涂料和屏蔽型耐热面层涂料配合使用,浇注的ZG00Cr13Ni4Mo超低碳不锈钢铸件距表面2.5～3mm处含碳量达到本体水平.

预渗碳处理对H13钢碳化铬覆层高温摩擦磨损性能的影响

利用光学显微镜、维式硬度仪、电子探针显微分析仪等分析方法,研究了预渗碳处理对H13钢碳化铬覆层质量以及高温耐磨损性能影响。结果表明:复合覆层(预渗碳+热反应扩散(TRD)处理)避免了贫碳层的出现,其硬度为2226 HV0.1,碳化铬覆层厚度平均为15μm;相比单一覆层,其厚度提升了4倍,硬度提升38%。高温摩擦磨损实验中,复合覆层高温耐磨损性能最优,摩擦系数稳定在0.307左右,磨损率为1.033×10^(-13)m^3/(N·m),约为单一覆层的1/7,为未处理H13钢的1/8,复合覆层的磨损机制主要是氧化磨损,单一覆层则是氧化磨损和磨粒磨损。

不锈钢离子渗碳后表面亮化处理方法对渗层形貌和性能的影响

奥氏体不锈钢离子渗碳后,表面覆盖了一层结合牢固、致密的黑色薄膜,不仅影响表面美观度,还影响了耐腐蚀性能。为了恢复不锈钢原有的颜色和提高渗碳不锈钢表面的耐腐蚀性,对其分别进行了机械法和电化学法亮化处理,并对亮化处理后不锈钢表面硬化层的表面形貌、组织结构、硬度及耐腐蚀性能做了比较。结果表明,与机械法相比,电化学亮化处理虽使不锈钢表面硬化层的厚度和硬度略有减小,但表面的耐腐蚀性能却有较大幅度的提高,用电化学法对渗碳不锈钢表面进行亮化处理是一种比较理想的处理方法。

金属基类石墨复合膜微观组织结构分析

应用非平衡闭合磁控溅射技术在渗碳淬火基体上制备了类石墨复合膜,用SEM、AFM和TEM分析了金属基类石墨复合膜的表面形貌和截面结构,并测试了类石墨复合膜的摩擦学特性。结果表明,类石墨复合膜是由柱状多晶过渡层+非晶梯度层+类石墨复合层组成的多层结构。

膏剂渗碳工艺及渗后热处理对其渗层耐磨性的影响

通过对膏剂渗碳工艺的试验及研究 ,找出了得到稳定的膏剂渗碳效果的方法 ,并进行了渗后不同热处理的耐磨性试验。结果表明 ,该工艺方法效果稳定 ,易于实现 ,尤其适于局部要求渗碳处理的工件 ,成本低廉 ,膏剂涂层以 5mm为宜 ,渗碳后经两次加热淬火后的试样具有更好的耐磨性。

基于含锆复合硅酸盐矿粉低碳钢树脂砂铸造防渗碳涂料

采用X射线衍射分析仪、热膨胀测试仪、数字显微镜等研究了含锆复合硅酸盐矿粉的组成结构和性能特点。基于含锆复合硅酸盐矿粉的防渗碳涂料,在ZG1Cr18Ni9Ti不锈钢叶轮树脂砂铸造生产中的应用实例,采用直读式光谱仪、能谱分析仪研究了该涂料对铸件表层的防渗碳效果。采用扫描电镜观察了涂层在铸件浇注并冷却后的微观形貌变化,分析了该涂料的防渗碳作用机理。结果表明,该涂料具有优良的悬浮性、涂刷性、渗透性、流平性和抗裂性,涂层强度高,发气量小;铸件打箱时涂层绝大部分能成片剥离,铸件表面光洁,防粘砂效果优良。含锆复合硅酸盐矿粉涂料能代替纯锆英粉涂料,有效防止树脂砂低碳钢铸件表面粘砂和渗碳,显著改善铸造生产环境,降低铸造生产成本。

不同润滑环境下石蜡浸润类石墨复合膜的摩擦特性

采用非平衡闭合磁控溅射技术在渗碳淬火基体上制备了类石墨复合膜,对该膜的表面进行了石蜡浸润处理,用POD销-盘磨损仪研究了石蜡浸润类石墨复合膜在不同润滑条件下同质对磨的摩擦学特性。研究表明,石蜡浸润处理能有效改善不同环境和工况下类石墨复合的膜摩擦特性,特别适合高速油润滑环境。

低碳钢固体渗碳的实验与研究

对20、20CrMoV钢的固体渗碳进行了较全面的实验及研究,包括钢的预备热处理、渗碳工艺、金相组织、最终热处理等;分析了渗碳层、硬度的影响因素,并总结摸索出固体渗碳的基本规律和工艺技术;实验证明:固体渗碳工艺简单、操作简单、成本低廉,不需要专门设备;渗碳件在性能上完全能够达到常规渗碳的要求,但固体渗碳的渗碳层偏薄,时间较长,只能适应单件、小批量的生产。

无机防渗碳自剥落涂料的制备与应用

通过分析现有防渗碳涂料存在的自剥落性差和防渗碳效果不佳等问题,采用水玻璃、玻璃粉、二氧化硅、氧化铝等原料制备出一种新型无机防渗碳涂料,并将该涂料涂于基材18CrMoNi钢表面进行渗碳热处理。结果表明:涂料粘结性好,干燥后形成的涂层致密光滑,同时具有良好的防渗碳效果,淬火自动剥落,具备优良的自剥落性。

轻石脑油制苯抗结焦抗渗碳防护涂层研究

针对轻石脑油制苯反应器的结焦和渗碳问题,采用在高温碳气氛中化学稳定,不引发催化结焦的SiO2作为涂层的主体材料制备防护涂层,在轻石脑油制苯反应器内进行1000h工况考核实验。实验结果表明,防护涂层与基体冶金结合、均匀致密,工况考核1000h后,涂层致密完整,未发生结焦和渗碳现象。同样条件下无涂层样品发生了明显的渗碳现象,样品表层中形成了粗大的碳化物相,经硬度测试,渗碳深度为150μm。本文提出的防护涂层具有良好的抗结焦和渗碳能力。

涂层厚度对气化模铸钢件表面含碳量的影响

用EPS做模型 ,干砂造型在负压的状态下浇注ZG2 5 ,系统研究涂层厚度对气化模铸造碳钢件表面含碳量变化。结果表明 ,适当的涂层厚度 ,铸件表面含碳量不会变化 ,随着涂层厚度的增加 。

新型金属结构材料中碳原子扩散行为的模拟研究

采用有限元法,模拟了用渗碳-脱碳化学热处理和外加涂层制备的新型金属结构材料中碳原子的扩散情况以及最终的碳浓度分布,分析了涂层尺寸对碳浓度分布的影响。结果表明,在涂层尺寸为0.4～0.5mm的条件下,渗碳过程中当外界碳势为1.48%(质量分数)、传质系数为1.34×10^(-7)m/s时或脱碳过程中当外界碳势为0%(质量分数)、传质系数为1×10^(-7)m/s时,材料比较容易获得外软内硬的力学性能。薄膜尺寸分别为0.4mm和0.5mm时,渗碳时间为900～1000s和1300～1400s,相应的脱碳时间为1800～1900s和2200～2300s时可获得最佳的扩散效果。