High-speed jet electrodeposition and microstructure of nanocrystalline Ni-Co alloys

The jet electrodeposition from watts baths with a device of electrolyte jet was carried out to prepare nano-crystalline cobalt-nickel alloys. The influence of the concentration of Co²⁺ ions in the electrolyte and electrolysis parameters, such as the cathodic current density, the temperature as well as the electrolyte jet speed, on the chemistry and microstructure of Ni-Co-deposit alloys were investigated. Experimental results indicated that increasing the Co²⁺ ions concentration in the bath, the electrolyte jet speed and decreasing of the cathodic current density and decrease of the electrolyte temperature all results in an increase of cobalt content in the alloy. Detailed microstructure changes upon the changes of alloy composition and experimental conditions were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD results show the Ni-Co solid solution was formed through the jet electrodeposition. Phase constitution of solid solution changes progressively under different electrolyte concentration. Alloys with low Co concentration exhibit single phase of face-centered cubic (fcc) structure; The Co concentration over 60.39 wt.%, the alloys are composed of face-centered cubic (fcc) phase and hexagonal close-packed (hcp) phase. Furthermore, the formation of the nanostructured Ni-Co alloy deposit is investigated. Increasing the Co²⁺ ions concentration in the bath, the cathodic current density, the electrolyte temperature and the electrolyte jet speed all result in the finer grains in the deposits. Additives such as saccharin in the electrolyte also favor the formation of the finer grains in the alloy deposits.     

脉冲镀Ni-Co合金镀层内应力及钴含量的研究

研究了脉冲镀Ni-Co合金的工艺,讨论了脉冲电镀中占空比及频率对镀层内应力及钴含量的影响.实验结果表明:镀层内应力随占空比的增加而降低,随脉冲峰值电流密度增加而升高,随温度的升高而降低.镀层中Co的质量分数则随温度的升高而升高.     

Electrochemical deposition and characterization of ZnCo alloys and corrosion protection by electrodeposited epoxy coating on ZnCo alloy

ZnCo alloys electrochemically deposited on steel under various deposition conditions were investigated. The influence of deposition current density, temperature and composition of deposition solution on the phase structure and corrosion properties of ZnCo alloys were studied. It was found that ZnCo alloy obtained from chloride solution at 5 A dm⁻² showed the best corrosion properties, so this alloy was chosen for further examination. Epoxy coating was electrodeposited on steel and steel modified by ZnCo alloy using constant voltage method. The effect of ZnCo alloy on the corrosion behavior of the protective system based on epoxy coating is interpreted in terms of electrochemical and transport properties, as well as of thermal stability.     

电沉积Ni-Co合金的研究

研究了氨基磷酸盐电沉积Ni-Co合金电解液组成及工艺条件对沉积层中Co含量的影响.并测定了Ni-Co合金沉积层中Co含量与Ni-Co与硬度的关系,以及影响Ni-Co合金沉积层内应力的因素.实验结果表明,将一定量的Co引入Ni沉积层,可以显著地提高其硬度;当在电解液中添加一定量的Ni-1添加剂后,能使Ni-Co合金沉积层的内应力为零.这些有益的实验结果为电铸加工使用寿命长、机械性能好的模具提供了一定的依据.     

Pulse reverse plating of Ni-Co alloys: Deposition kinetics of Watts, sulfamate and chloride electrolytes

Fundamental electrochemical properties of electrolyte systems are the prerequisite for the development of a successful pulse deposition process. Three different electrolyte systems for the galvanic deposition of nickel cobalt alloys (chloride, Watts and sulfamate type) were investigated in order to reveal underlying deposition mechanisms and rate determining factors. The electrochemical experiments were supported by X-ray fluorescence analyses of the alloy composition in dependence on the current density and the type of bath. A special focus was set on the investigation of the passive (oxide) layer formation by the anodic pulses.The choice of electrolyte system strongly influences the reaction mechanism and thus the alloy deposition. Also the cobalt content within the deposited layer varied strongly in dependence on the electrolyte system used. While sulfamate and Watts baths show an ability for passive layer formation, the chloride bath exhibits a lower proneness to passivation, accompanied by pit formation     

电铸镍钴合金中内应力的影响因素

讨论了硫酸盐体系中影响镍钴合金电铸层内应力的因素。结果表明,内应力随钴离子质量浓度的增加而升高;随电流密度的增大先升高后降低,在6A/dm2附近时应力最大;随温度的升高而降低;pH在3.0~4.5时应力较小。加入0.2~0.5g/L添加剂可有效消除内应力。     

Electrodeposition of Ni, Co and Ni-Co alloy powders

In this paper the polarization characteristics of the processes of Ni and Co powders and Ni-Co alloy powders electrodeposition from ammonium sulfate containing supporting electrolyte are investigated as a function of Ni²⁺ and Co²⁺ ions concentrations. It is shown that the correct polarization curves for Ni and Co powders and Ni-Co alloy powders electrodeposition could be obtained only after IR drop correction, since the total current density of electrodeposition at the most negative potential of −1.4 V versus Ag|AgCl is extremely high (up to about 3-6 A cm⁻²) as a consequence of simultaneous hydrogen evolution which starts immediately after the beginning of metals (alloys) deposition. After determining the current density for hydrogen evolution and its subtraction from the total current density, correct polarization curves for Ni and Co powders and Ni-Co alloy powders electrodeposition are obtained. They are found to be different for each ratio of Ni²⁺/Co²⁺ ions concentration. It is also concluded that the shape of the polarization curves in all cases is practically defined by the shape of the polarization curve for hydrogen evolution. The morphology and composition of electrodeposited powders were also found to be sensitive to the ratio of Ni²⁺/Co²⁺ ions concentration.     

Electroplating of a Co–Cu alloy from a citrate bath containing boric acid

The effects of bath composition, current density and temperature on cathodic polarization, cathodic current efficiency of codeposition, composition and structure of Co–Cu alloys electroplated on a steel substrate from citrate baths have been studied. Addition of boric acid to citrate electrolyte increases the percentage of Co in the deposits and improves the quality of these deposits. The cathodic current efficiency of the baths is relatively high and increases with increases in the metal content in the bath and the current density but decreases with temperature. The composition of the deposit is controlled by the applied current density. At low current densities, Cu‐rich alloys were obtained. At higher current densities, the composition of the alloys was controlled by the limiting current density of Cu codeposition. The Co content of the deposits increases with increases in the metal content in the bath and the temperature. The structure of the deposited alloys was characterized by anodic stripping and X‐ray diffraction techniques. The deposited alloys consisted of a single solid solution phase with a face‐centred cubic structure. © 2000 Society of Chemical Industry     

Electrodeposition of Ni–Co alloys from sulfamate baths

The paper describes the results of electrochemical investigations of Ni–Co deposition from a sulfamate bath in the presence of boric acid and two additives. The individual deposition of nickel was shown to be partly inhibited by the adsorption of sulfamate ions at low polarization; such inhibition was not observed for cobalt. The introduction of saccharin at 100 ppm, with a wetting agent seems to hinder sulfamate adsorption and Ni deposition departs at less cathodic potentials. The presence of cobalt has no effect on nickel deposition, whereas cobalt deposition is hindered by the presence of nickel in the bath. Galvanostatic deposition was carried out at the surface of a RDE and with a rotating cylinder Hull cell. At low current densities deposits with a Co content of approx. 40% were produced, but this content was shown to decrease with the applied current density. Examination of experimental data showed that cobalt deposition is diffusion-controlled and that Co content decreases with the applied current density relative to the limiting current density.     

氨基磺酸盐电解液中金属镍的阳极行为

研究了电解镍阳极和含硫的活性镍阳极在氨基磺酸盐电解液中的阳极行为，阳极极化曲线的测定结果表明，电解镍阳极较之含硫活性镍阳极容易钝化得多，前者的临界钝化电流密度仅为后者临界钝化电流密度的１／４０，工艺实验结果表明，含硫活性镍阳极在宽的电位范围内进行金属镍的电化学溶解反应；而电解镍阳极在发生镍的阳极溶解反应的同时，还进行着ＮＨ２ＳＯ３离子的氧化反应，采用电解镍阳极对电解液进行了小电流电解１０～４０Ａｈ     

由氨基磺酸盐和硫酸盐电解液电沉积Ni－Co合金的对比研究

通过大量实验对比了氨基磺酸盐和硫酸盐两种电解液电沉积Ｎｉ－Ｃｏ合金Ｃｏ含量的影响因素，以及Ｎｉ－Ｃｏ合金沉积层的硬度、内应力与Ｃｏ含量的关系。结果表明，与硫酸盐电解液相比，从氨基磺酸盐电解液中沉积的Ｎｉ－Ｃｏ合金硬度高、内应力低。     

Influence of cobalt on manganese incorporation in Ni–Co coatings

The effect of alloying <1 wt% Mn with plain Ni, Ni–Co alloys and plain Co coatings in terms of the structure and properties has been studied. The alloys were electrodeposited from an additive free sulphamate electrolyte. The Mn concentration in the electrolyte was maintained at 5 g L⁻¹ so as to obtain <1 wt% Mn content in the alloy coatings. The Energy Dispersive X-ray analysis (EDX) showed that the Mn content reduced from 0.97 to 0.05 wt% with increase in Co content from 0 to 98 wt% in the alloy coating. An increase in microhardness was obtained on the addition of Mn to Ni/Ni–Co alloys. The X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) studies revealed a change in crystal structure and morphology. Pin-on-disc tribology test revealed better wear performance of Ni–18 wt%Co–Mn alloy coating compared to the other Ni–Mn/Ni–Co–Mn alloy coatings.     

Electrodeposition of Zn–Co alloy coatingsfrom sulfate–chloride electrolytes

The composition, surface morphology and appearance of Zn–Co alloy deposits as a function of current density, electrode potential and Co2+ concentration in the electrolyte was studied. It was found that coatings of good quality with low (1%) Co content are formed at a current density of 0.2Adm–2 and with high (6.5%) Co content at 2Adm–2 from electrolytes containing 1.0M Co2+ under galvanostatic conditions. The potentiodynamic dissolution of coatings with Co content of 6.5% indicates successive deposition of Co enriched phases and a pure Zn phase. The Zn–Co alloys are more corrosion resistant than zinc but are less resistant than cobalt.     

氨基磺酸体系Co-Ni合金电化学共沉积行为及动力学机理

通过稳态阴极极化和电化学交流阻抗(EIS)等方法,研究了在不同钴镍金属离子比例的氨基磺酸电解液中,Co-Ni合金的电化学共沉积行为。结果表明在氨基磺酸体系中,导致Co-Ni合金异常共沉积行为的原因和在硫酸盐,或氯化物体系中的不同。不是由于Co^2 抑制了Ni的沉积,而是由于NH2SO3^-作为双齿配体形成的异核络合物在电极表面吸附,阻滞了镍离子的还原过程。并且以晶体场理论为基础解释了Co^2 和NH2SO3^-形成的高自旋络合物,比Ni^2 所形成的络合物具有较高的晶体场稳定化能(CFSE),容易分解。因此吸附在电极表面的氨基磺酸根离子对Co2^2 沉积的阻滞作用小于对Ni2^ 的。这样就导致了在氨基磺酸电解液体系中Co^2 的优先沉积。阳极线性扫描曲线表明．钴镍合金中镍含量越高,沉积层在热力学上越稳定,耐蚀性也越好。同时通过EIS的测试,利用等效电路的分析方法和交流阻抗谱解析理论,提出了氨基磺酸电解液中Co-Ni合金共沉积的动力学机理,较好地解释了实验结果。     

(Zn-Co)-TiO2复合电镀的工艺研究

研究了微酸性氯化物体系中（Ｚｎ－Ｃｏ）－ＴｉＯ２复合电镀的工艺,探讨了镀液组成及工艺条件对复合镀层中Ｃｏ及ＴｉＯ２含量的影响,得到了（Ｚｎ－Ｃｏ）－ＴｉＯ２复合电镀的最佳工艺。并对（Ｚｎ－Ｃｏ）－ＴｉＯ２复合镀层的耐蚀性进行了考察,与Ｚｎ－Ｃｏ合金镀层和锌镀层的耐蚀性进行了对比。     

复合电镀制备磨低拱高磁瓦金刚石砂轮

采用镍-钴合金镀液电镀出磨低拱高磁瓦的金刚石砂轮。针对弧面砂轮的形状特点,在上砂和加厚时采用阴极绝缘屏蔽,防止砂轮的凸出部位因电力线过分集中造成镀层过厚,从而提高了砂轮镀砂的均匀性,使磨削出产品的尺寸达到了客户的要求。     

Electrochemical studies of zinc–cobalt alloy coatings deposited from alkaline baths containing glycine as complexing agent

Co-deposition of Zn–Co alloy coatings that were electrodeposited from weakly alkaline glycine solutions has been studied by cyclic voltammetry. Scanning electron microscopy (SEM), energy depressive spectroscopy (EDS), and X-ray diffraction (XRD) analyses were used to study surface morphology, chemical composition, and phase structure of the coatings. Corrosion behavior of the coatings was also studied using potentiodynamic polarization tests in 3.5 wt% NaCl solution. Cyclic voltammetry results showed that in Zn–Co deposition from an alkaline bath in the presence of glycine, cobalt deposited at a potential near to that of zinc together with successful co-deposition of Co and Zn. It was also shown that reduction–oxidation (redox) reactions of Zn–Co alloy deposits were quasi-reversible and resulted in deviation of electrodeposited alloys from the equilibrium phase diagrams. The corrosion resistance of the deposits was also highly influenced by the composition and morphology of the coatings. Overall, Zn–Co deposit containing 0.89 wt% Co showed that the highest corrosion resistance among the coatings that was due to its single phase structure and fine morphology.     

Influence of V-containing species on formation and corrosion resistance of PEO coatings developed on AZ31B Mg alloy

The defects, micropores, and microcracks on the plasma electrolytic oxidation (PEO) coating severely affect the long-term anti-corrosion feature. Inclusion of additives in the electrolyte is a feasible and effective strategy to attain the more intact PEO coating. The PEO coatings are fabricated on AZ31B Mg alloys in an silicon-based electrolyte with Na₃VO₄ (OPEO), NaVO₃ (MPEO), and V₂O₃ (VPEO), respectively, to explore the influence of additives on the corrosion resistance. MPEO sample has the smallest poriness and pore size unfolding the best anti-corrosion resistance, which is also consistent with the electrochemical analysis. Even after 336 h salt spray test, the MPEO coating exhibits the least corrosion. The excellent anti-corrosion performance of MPEO sample is the synergistic effect of inorganic salts and multiple metal oxides generated in the formation of PEO coating. Inclusion of inorganic salt with valence change metal is a feasible pathway to achieve the compact PEO coating since multiple metal oxides could be produced and deposited in the PEO coating during the fabrication.     

Effects of thiourea and urea on zinc–cobalt electrodeposition under continuous current

The effect of thiourea and urea on zinc-cobalt alloys obtained from chloride baths under continuous current deposition are described and discussed. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and an X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. The use of additives does not refine the grain size of the Zn–Co alloy and an especially porous alloy was produced in the presence of urea. The preferred crystallographic orientations of zinc–cobalt alloys do not change in the presence additives. Zinc–cobalt alloys were without texture in the presence and absence of additives. Also, in the absence of additive and in the presence of urea, the XRD lines of the Zn–Co alloys are slightly shifted with respect to the pure zinc XRD lines, whereas, in the presence of thiourea, the XRD lines are not shifted. The alloy composition was examined using Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases slightly from 1.04 to 0.91 wt.% in the presence of urea and in the presence of thiourea it increases from 1.04 to 7.70 wt.%. Voltammetric studies show that thiourea increases the reduction rate of cobalt. This explains the increase in cobalt percentage in the alloy in the presence of thiourea.     

峰值电流密度对脉冲镀镍钴合金纳米镀层机械性能的影响

研究了峰值电流密度对脉冲镍钴合金纳米镀层的成分、晶粒尺寸、显微硬度、抗拉强度的影响.结果发现:在一定范围内,峰值电流密度的增大,可以降低镀层钴含量、表面粗糙度和晶粒尺寸,使菜花胞状结构更明显,提高镀层显微硬度(最高可达600 kg/mm2)和抗拉强度(最高可达1 200 MPa).然而,峰值电流密度太大又会使显微硬度和强度下降.与采用类似方法制得的纯镍纳米镀层相比,镍钴镀层的显微硬度并未明显升高.这说明在该纳米材料中,固溶强化效果并不很明显,而以细晶强化为主.