Si3N4/Ni nanocomposite formed by electroplating:Effect of average size of nanoparticulates

Properties of Si3N4/Ni electroplated nanocomposite such as corrosion current density after long time immersion,roughness of obtained layer and distribution of nanometric particulates were studied.Other effective factors for fabrication of nanocomposite coatings were fixed for better studying the effect of the average size of nanoparticulates.The effects of the different average size of nanometric particulates(ASNP)from submicron scale(less than 1μm)to nanometric scale(less than 10 nm)were studied.The nanostructures of surfaces were examined by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and atomic force microscopy(AFM).Corrosion rates of the coatings were determined using the Tafel polarization test.It is seen that decreasing the ASNP will lead to lower corrosion current densities;however,in some cases,pitting phenomena are observed.The roughness illustrates a minimum level while the distribution of nanometric particulates is more uniform by decreasing the ASNP.The effects of pulsed current on electrodeposition(frequency,duty cycle)and concentration of nanoparticulates in electrodeposition bath on trend of obtained curves have been discussed.Response surface methodology was applied for optimizing the effective operating conditions of coatings.The levels studied were frequency range between 1 000 and 9 000 Hz,duty cycle between 10%and 90%and concentration of nanoparticulates of 10-90 g/L.     

Characterization of Ni-W/MWCNT nanocomposite layers formed by pulsed electrochemical deposition

Ni-W/MWCNT nanocomposite layers with high concentration and uniformly dispersed MWCNT nanoparticulates were formed by pulsed electrochemical deposition technique. Nanocomposite layers were analyzed by SEM, AFM, microhardness and tafel tests. Effect of frequency of pulsed current and concentration of MWCNT nanoparticulates in metallic matrix have been investigated on electrochemical and mechanical properties of obtained layers. It has been concluded that both of the electrochemical and mechanical properties of Ni-W/MWCNT nanocomposite layers formed by pulsed current were improved significantly with respect to Ni-W layer with out nanoparticulates. It was revealed that the obtained results were not only concerned by the concentration of MWCNT nanoparticulates in the nanocomposite layer, but also influenced by the distribution of nanoparticulates in metallic matrix.     

Ni nanocomposite films formed by Ni nanowires embedded in Ni matrix using electrodeposition

Ni nanocomposite films formed by Ni nanowires embedded in Ni matrix(Ni nanowire/Ni composite films)were fabricated by electrodeposition combined with supersonic stirring in a conventional Watts'bath containing Ni nanowires with diameter about 30 nm.The deposition temperature-dependent microstructure,crystal orientation,lattice constant and corrosion behavior of the Ni nanowire/Ni composite films were investigated by field emission scanning electron microscope,X-ray diffraction and potentiodynamic polarization tests,respectively.And the possible mechanism was discussed.It is found that to some extent,the deposition temperature has an impact on the microstructure,crystal orientation,lattice constant and corrosion property of the Ni nanowire/Ni composite films.The Ni nanowire/Ni composite films prepared at 50℃exhibit a novel inter-twisted-nanowire microstructure and have the best corrosion resistance.     

AZ91镁合金脉冲电沉积Ni-SiC纳米复合涂层的磨损与腐蚀性能

为了改善AZ91镁合金的表面性能,在含0-15g／LSiC纳米颗粒的改进的瓦特槽中,采用脉冲电沉积得到不同SiC含量的Ni-SiC纳米复合涂层。采用扫描电子显微镜（SEM）研究涂层的形貌,采用能谱仪（EDs）测试涂层的SiC含量。从15g／LSiC槽中电沉积得到的样品,其涂层的显微硬度提高了600％。采用动电位极化法研究包覆AZ91镁合金的腐蚀行为。结果表明,样品的耐腐蚀性能明显提高,即腐蚀电流密度从未包覆样品的0．13mA／cm2降低到槽中含15∥LSiC电沉积包覆样品的1．74x101mA／cm2,腐蚀电位从未包覆样品的-1．6V增加到槽中电沉积包覆样品的-0．31V。使用盘销摩擦测试仪评估了包覆和未包覆样品的耐磨性能,包覆样品的磨损量比未包覆的小8倍。     

Structure and mechanical properties of nickel/carbon nanocomposite films formed by microwave plasma-assisted deposition technique from argon-acetylene gas mixture

The structure and mechanical properties of nickel/hydrogenated amorphous carbon (Ni/a-C:H) films formed by microwave plasma-assisted deposition technique were investigated as a function of the carbon content using various methods: Rutherford backscattering spectroscopy (RBS), Raman spectroscopy and tribometry. The size of carbon clusters determined by Raman spectroscopy in Ni/a-C:H films deposited in gas mixtures containing 40 and 60% of C₂H₂, and in nickel free a-C:H films was 1 and 4 nm, respectively. However, the amorphous Ni/a-C:H films deposited from a gas mixture containing 60% of C₂H₂ exhibited the lowest friction coefficient (∼ 0.04), at the same time the nanohardness of these films was ∼ 7 GPa.     

Nanostructure and corrosion behaviors of nanombe formed Ti-Zr alloy

In order to investigate the nanostructures and corrosion behaviors of Ti-Zr alloys, nanotube formed Ti-Zr(10%, 20%, 30% and 40% in mass fraction) alloys were prepared by arc melting and the condition of controlling nanostructure was at 1 000 °C for 24 h in argon atmosphere; formation of nanotubes was conducted by anodizing a Ti-Zr alloy in H₃PO₄ electrolyte with a small amount of fluoride ions at room temperature. The corrosion properties of specimens were examined through potentiodynamic test (potential range of −1 500–2 000 mV) in 0.9% NaCl solution by using potentiostat. Microstructures of the alloys were observed by optical microscope(OM), field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD). Diameter of nanotube does not depend on Zr content, but interspace of nanotube predominantly depends on Zr content, which confirms that ZrO₂ oxides play a role to increase the interspace of nanotube formed on the surface.     

退火处理对Ni-Al纳米复合镀层循环氧化性能的影响

研究在500℃真空扩散不同时间条件下的扩散合金化对Ni-Al纳米复合镀层的结构与抗循环氧化性能的影响。结果表明：扩散不仅导致Ni-Al纳米复合镀层的基体Ni晶粒粗化,还导致Al固溶在基体Ni中,Ni与Al之间形成金属化合物;随着扩散合金化时间的延长,Ni-Al合金涂层中的空洞减少,从而减少了合金涂层在循环氧化过程中出现的穿透性裂纹和内氧化,抑制了氧化膜剥落区瘤状NiO的形成,提高了Ni-Al合金涂层的抗循环氧化性能。     

Friction and wear behavior of Cu-CeO2 nanocomposite coatings synthesized by pulsed electrodeposition

The friction and wear behavior of copper matrix nanocomposites reinforced with nanosized ceria particles, synthesized by pulse electrocodeposition technique, have been investigated. Tests have been carried out under dry sliding conditions by rubbing against a steel ball at varying loads ranging from 4 to 20 N and at constant speed of 11 rpm using a ball-on-disk wear tester. The experimental results indicate that the wear resistance of copper composite is superior to that of pure copper at all the loads and it improves with the increasing amount of ceria in the copper matrix. The friction coefficient and wear rates increase with the increase in applied load. When the load increases from 4 to 20 N, the transition of wear regime from local damage to delamination of a mechanically mixed layer (MML) occurs.     

高速电喷镀纳米复合镀层组织与性能研究

采用高速电喷镀工艺制备纳米Ni／PTFE复合镀层。研究了电流密度、镀液中纳米PTFE含量等工艺参数对镀层性能的影响。研究结果表明，提高电流密度可显著提高复合镀层的沉积速率、镀层与基体的结合强度以及镀层的耐腐蚀性：镀层与基体的结合强度随镀液中PTFE的加入量的改变而变化，当加入量为10ml／L时，镀层经30次热震试验后，镀层无明显剥落：Ni与纳米PTFE共沉积可显著改善镀层的耐腐蚀性能。     

Microstructure ofin situ MoSi2/SiC nanocomposite coating formed on Mo substrate by displacement reaction

The microstructure of an in-situ Mosi₂/β-SiC nanocomposite coating formed by the solid-state displacement reactions of Si deposited by chemical vapor deposition (CVD) with Mo-carbide layers at 1100°C, which had previously been formed on the surface of a Mo substrate by a CVD process, was investigated. The Mo-carbide layers formed by the simultaneous CVD of Mo and carbon at 900°C for 5 h using a gas mixture of C₂H₄−MoCl₅−Ar consisted of two layers, an inner layer of Mo₂C and an outer layer of MoC. While the monolithic MoSi₂ coating showed a typical colummar microstructure perpendicular to the Mo substrate, the MoSi₂/β-SiC nanocomposite coating formed by the solid-state displacement reactions between the Mo-carbide layers and Si was composed of equiaxed MoSi₂ grains with an average size of 150–500 nm and β-SiC particles with an average size of 80–105 nm. The β-SiC particles exhibited an oblate-spheroidal shape and were located mostly at the grain boundaries of MoSi₂. The volume percentage of β-SiC particles ranged from 18.5 to 29.2% with respect to the carbon concentration in Mo-carbide layers.     

Pulsed eddy current testing with variable duty cycle on rivet joints

In pulsed eddy current testing, repetitive excitation signals with different duty cycles have different spectral representations. This work studies the influence of duty cycle on the ability to detect holes and EDM notches beneath rivet heads in subsurface layers of stratified samples. Feature patterns for the integrity of rivet joints are proposed and verified. The proposed method has the added advantage in that no reference sample is needed while employing multiple pulse measurements, with different pulse widths. Experimental testing and modelling approaches are discussed in connection with defect depth quantification, which can be extended to the quantification of complex defects.     

真空热处理对快淬纳米复合NdFeB电磁特性的影响

采用真空快淬技术制备低Nd含量的NdFeB纳米复合磁性材料,通过差示扫描量热法(DSC)、X射线衍射(XRD)、振动样品磁强计(VSM)和微波矢量网络分析仪等手段研究了真空热处理前后样品微观结构和电磁特性的变化。DSC结果显示在510℃和630℃处出现两个放热峰,在稍微高于这两个温度分别热处理后,相对于快淬态样品,材料的磁导率(μ')和磁损耗(μ″)降低,并且磁损耗出现多重频散特性,同时复介电常数减小,特别在2 GHz处ε″分别为-103.7(540℃)和ε″为-245.3(650℃)。根据传输线理论模拟计算涂层的反射损耗,发现快淬态样品在3.7 GHz下厚度为1.5 mm时最小反射损耗为-5.3 dB;而热处理后的样品在12 GHz处获得最小反射损耗,分别为-3.3 dB(540℃)和-2.1 dB(650℃)。     

Ni-7Cr-4Al纳米复合镀层的氧化和热腐蚀性能(英文)

采用复合电镀技术,通过向普通硫酸镍电镀液中加入纳米Cr和Al颗粒,在Ni基材上制备了一种Ni-7Cr-4Al(质量分数,%)纳米复合涂层,对其在800°C下的空气氧化和750°C下75%Na2SO4+25%Na Cl混合熔盐热腐蚀性能进行研究。作为对比,对相同工艺制备的Ni-11Cr纳米复合镀层和纯Ni镀层的氧化和热腐蚀性能进行分析。Cr和Al纳米颗粒弥散分布在20~60 nm的纳米Ni中,与Ni-11Cr纳米复合镀层和纯Ni镀层相比,Ni-7Cr-4Al纳米复合镀层由于能快速形成氧化铝膜而表现出更优异的抗氧化性能,同时氧化铝膜的快速形成也提高了涂层的热腐蚀性能。     

占空比对Ni-SiC纳米复合镀层性能的影响

采用单脉冲电镀技术,在瓦特型镀液中,制备了Ni-SiC纳米复合镀层。采用X射线衍射仪(XRD)扫描电镜(SEM)分别表征了Ni-SiC纳米复合镀层相结构和表面形貌,通过静态浸泡腐蚀实验、磨损实验和高温氧化性能研究了复合镀层的性能。结果表明,在不同占空比下,Ni-SiC复合镀层的组织主要为Ni晶体;当占空比为70%时,复合镀层的显微硬度最大,为376 HV,摩擦系数最小;900℃、100 h高温氧化增重最小,为7.453 mg·cm-2为0.37。在3.5%Na Cl溶液中静态浸泡30 d后,占空比为70%时的复合镀层的失重最小,失重为3.063 mg·cm-2。     

电流密度对海水淡化用铝合金微弧氧化陶瓷膜层耐蚀性的影响

在硅酸盐体系中研究了双极性脉冲电源的电流密度对6061铝合金微弧氧化的影响。结果表明,电流密度对膜层的生长、形貌及耐蚀性具有明显的影响;电流密度为15.0 A/dm2时,起弧时间最短为86 s,且膜层形貌均匀、致密,腐蚀电位E0和腐蚀电流密度Icorr分别达到-0.526 72 V和5.287×10-8A/cm2,表现出良好的耐蚀性能。用高浓度海水喷淋腐蚀试验表明来自海水中的Cl-阴离子只能进入MAO膜层的疏松表层,生成可溶性的Al-O-Cl络合物,造成表面出现大量"海绵絮状"孔洞,但Cl-、SO24-等阴离子无法进到膜层内部致密层,从而基体不被腐蚀。     

Influence of the duty cycle on structural and mechanical properties of oxide layers on Al-1050 by a plasma electrolytic oxidation process

Oxide layers were prepared on Al-1050 substrates by an environmentally friendly plasma electrolytic oxidation process using an alkaline solution of Na₂SiO₃ (8 g/L) and NaOH (3 g/L) as the electrolyte. The effects of three different duty cycles (20%, 40%, and 60%) on the structure and hardness of the oxides were investigated. XRD analysis revealed that the oxides were mainly composed of α-Al₂O₃, γ-Al₂O₃, and mullite. The proportion of each phase depended on various electrical parameters, such as the duty cycle and frequency. The morphology, thickness, and the elemental distribution of the oxides were examined by scanning electron microscopy and energy dispersive spectroscopy. The thicknesses of the oxides were found to vary from 20 μm to more than 60 μm for various duty cycles, when identical treatment durations were used. The oxidation treatment also resulted in good adhesion between the oxide layer and the substrate. SEM images indicated that the oxide layers formed at the 60% duty cycle exhibited relatively coarser surfaces with larger pore sizes and sintering particles, and slower growth rates than did those formed at the 20% duty cycle, under identical treatment durations. The oxides prepared at the 20% duty cycle showed smooth surfaces. The oxides layers were found to improve the micro-hardness of Al-1050. In particular, the oxide layers formed at the 40% duty cycle exhibited relatively better micro-hardness owing to their compact microstructures.     

The effect of additives on the pulsed electrodeposition of copper

Abstract

The pulsed electrodepostion of copper has been systematically investigated from a copper sulphate bath. Pulse duty cycles of 5–80%, at frequencies from 10 to 100 Hz with current densities ranging from 2·5 to 7·5 A dm^?2 were employed. The influences of pulsed current duty cycle, peak current density and frequency on the thickness and hardness of the copper deposit, current efficiency and throwing power of the plating process were studied. The effect of additives, polyethylene glycol and di-sodium EDTA on the properties of deposit were investigated.     

电沉积电位对锌镍合金镀层耐蚀性的影响

采用电化学沉积方法在DH36船板钢表面制备了锌镍合金镀层。采用扫描电镜(SEM),能谱仪(EDS)和X射线衍射仪(XRD)等研究了电化学沉积电位对锌镍合金镀层形貌、化学成分和晶体结构的影响。结果表明:随着沉积电位的升高,锌镍合金镀层由无法覆盖整个基底表面到均匀致密覆盖,再到较大微纳米颗粒层覆盖,证明沉积速率越来越大。由EDS和XRD分析可知,在较低电位下沉积,锌镍电沉积过程属于正常共沉积,而在较高电位沉积时,锌镍电沉积过程属于异常共沉积。电化学极化曲线测试表明,在电沉积电位为-1.2 V时所获得的锌镍合金镀层的耐腐蚀性最好。     

Preparation of nanocomposite thoriated tungsten cathode by swaging technique

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