Influence of pulse parameters on the microstructure and microhardness of nickel electrodeposits

Square-wave cathodic current modulation was used to electrodeposit fine-grained nickel from an additive-free and saccharin-containing Watts bath. The influence of pulse on-time, off-time, peak current density and saccharin on the grain size, surface morphology, crystal orientation, and microhardness was determined. The study showed that at constant off-time and peak current density, the crystal size of the deposits was found initially to decrease with pulse on-time before it started to increase with further increase in on-time. The crystal orientation progressively changed from a (111) texture at the on-time of 0.1 ms to a strong (200) texture at an on-time of 8 ms. An increase in the pulse off-time at constant on-time and peak current density resulted in a progressive increase in crystal size. However, the crystal orientation remained unaffected with increasing off-time. An increase in peak current density resulted in considerable refinement in crystal size of the deposits. The crystal orientation progressively changed from an almost random distribution at the lowest peak current density of 0.2 A/m² to a strong (200) texture at a peak current density of 2.0 A/m². The nanocrystalline nickel with grain size in the order of 30 nm can be produced from saccharin-containing Watts' baths. In contrast, when using an organic-free Watts' bath and similar pulse-plating conditions, the grain size can only be refined down to about 80-100 nm. The microhardness of deposits is related with grain size: when the grain size is large, the microhardness is consistent with Hall-Petch law (HPL); when the grain size is ultrafine, “nano-effect” would be generated, the microhardness is against HPL.     

Diffusion-elastic phenomena in nickel and cobalt electrodeposits plated on to strip cathodes

A quantitative analysis was made of the post-deposition increase of the internal tensile stress in nickel and cobalt electrodeposits using an approach based on the diffusion-elastic phenomena. Equations were derived for the determination of the amount and the effective diffusion coefficient of hydrogen, which leaves the deposit immediately after plating. The experimental results are processed using these equations and the results are compared with data in the literature. The role played by hydrogen desorption in increasing the tensile stress after the electrodeposition current is switched off was confirmed.     

Property enhancement of nickel electrodeposits by anodic current pulses

The yield and tensile strengths of nickel electrodeposits were increased by a factor of three by the periodic imposition of an anodic current pulse. The time periods between pulses were much longer than those used in periodic reversal plating. The increased strength was attributed to grain refinement resulting from nucleation on surfaces which became passivated during the anodic pulses. The reduced adhesion between layers plated between pulses resulted in a reduction in the coefficients of friction.     

Effect of substrate pretreatment on the porosity in thin nickel electrodeposits

Substrate pretreatment affects the porosity of thin nickel electrolytic coatings which is a combined function of the composition and the roughness of the substrate surface. Electropolishing the substrate surface is an effective method of reducing coating porosity, whereas coatings plated on either electroetched or mechanically ground substrates are relatively porous owing to the remaining oxide layer on the substrate and the increased roughness of the substrate. For nickel coatings plated on mechanically ground rough substrates, the relationship between nickel porosity, apparent coating thickness and substrate roughness has been examined.     

Porosity of nickel electrodeposits on mild steel using electrochemical impedance spectroscopy

Abstract

Impedance spectroscopy recorded at the open circuit potential in 1M H₂SO₄ at 293 K is shown to provide a convenient test for detecting the degree of through porosity in electroplated nickel coatings, electrodeposited from a Watts bath, on mild steel. The impedance data can be interpreted in terms of a simple equivalent circuit, and the corrosion resistance provides a reliable guide to the quality of the deposit. The quantitative estimation of porosity from these data is considered.     

退火温度对电沉积纳米晶镍组织结构与显微硬度的影响

采用脉冲电沉积法制备纳米晶镍,分析了退火温度对纳米晶镍组织结构与显微硬度的影响。利用差热分析仪、扫描电镜、X射线衍射仪及显微硬度计对纳米晶镍的热稳定性、表面微观形貌、晶粒尺寸和显微应变及显微硬度进行了表征。结果表明,随着退火温度的升高,纳米晶镍的晶粒尺寸从室温时的20 nm左右逐步长大到400℃时的120 nm左右;显微应变从室温时的0.47%下降到400℃时的0.08%;显微硬度先上升,从室温时的530 HV0.01左右上升到200℃时达最大值660 HV0.01左右,此后显微硬度迅速下降,到400℃时只有330 HV0.01左右。     

Influence of lower current densities on the residual stress and structure of thick nickel electrodeposits

Thick Ni electrodeposits, with thicknesses ranging from 18 to 90 μm, have been produced from sulfamate baths using very low current densities (1.5-5 mA cm⁻²). Increasing grain sizes, with a corresponding decrease in the hardness values, and more columnar grain morphologies were observed with increasing current densities in the deposits. The anisotropy in the mechanical properties of the deposits were found to correlate strongly with the deposit texture, where the change from a < 101> dominated orientation at 1.5 mA cm⁻² to a < 001> orientation at the higher (5 mA cm⁻²) current density led to a corresponding decrease in the indentation modulus values for the respective Ni films. The residual stress values measured in the deposits (75-136 MPa) were found to be comparable to literature values of deposits plated at higher current densities, which rules out any potential advantage from the use of such low current densities for producing lower residual stresses.     

熔烧状态对Co基合金涂层显微结构及硬度的影响

采用高频感应真空熔覆技术,制备钴基合金涂层.使用扫描电子显微镜观察涂层在不同深度的组织结构,用X射线能谱仪(EDS)探测涂层的化学元素组成,用显微硬度计测量涂层不同深度的显微硬度值.试验结果表明,熔烧状态的不同对涂层和基体化学元素之间扩散程度有显著的影响.熔烧时间越长,扩散程度越大.钴基合金涂层的硬度显著高于Q235钢基体,其显微硬度随着熔烧时间的延长而略有降低,但其硬度更均匀.     

Effects of in situ nickel particle addition on the microstructure and microhardness of Sn–Ag solder

Abstract

In this study, various amounts of Ni particles were added in situ to Sn–3·5 wt-%Ag lead free solder to form new composite solders. Copper substrates were then dipped into these solders and aged at 150°C for 0, 25, 225, or 1000 h. The microstructure and microhardness of the as solidified solder and the aged solder/copper couples were investigated. Experimental results revealed that the addition of Ni particles increased the microhardness of the composite solder. Ni additions of less than 3 wt-% yielded a microstructure of β-Sn grains surrounded by a eutectic mixture of Ag₃Sn and a Sn rich matrix. An intermetallic compound of Ni₃Sn₄ particles was dispersed throughout the eutectic. For 5 wt-%Ni addition, the Ni₃Sn₄ phase and the remaining Ni particles were agglomerated. In the case of copper substrate dipped with a thick layer of composite solder, water quenched and then aged at 150°C, the induced (Ni, Cu)₃Sn₄ particles coarsened and agglomerated. Additionally, the intermetallic (Cu, Ni)₆Sn₅ compound layer formed at the solder/Cu interface thickened with increasing Ni content.     

选择性还原-磁选回收镍渣中的有价金属

采用选择性还原-磁选工艺富集某镍渣中的镍、铜,通过控制还原过程参数实现选择性还原。结果表明：添加熔剂并适当提高渣料的碱度（CaO与SiO2质量比）有助于镍、铜的富集;对碱度0.15、还原温度1200℃、还原时间20 min、内配煤量5%（质量分数）的优化条件下得到的还原样品,通过磨矿-磁选获得镍、铜、铁品位分别为3.25%、1.20%、75.26%的精矿,镍、铜、铁的回收率分别为82.20%、80.00%、42.17%,实现了镍、铜相对于铁的选择性富集;选择性还原-磁选没有显著降低S、P的含量,两者在工艺过程中的行为需要进一步研究。     

Use of the reverse pulse plating method to improve the properties of cobalt-molybdenum electrodeposits

Conditions leading to cobalt-molybdenum (Co-Mo) electrodeposits with high Mo percentages were studied. Deposits prepared by means of direct current electroplating showed a large amount of cracks. Maximum amount of Mo in the films was attained by applying deposition potentials in the − 1200 mV to − 1300 mV range. Reverse pulse plating mode has been proved useful for obtaining nanocrystalline, low stressed Co-Mo deposits with similar Mo percentages as in direct current conditions (35-40 wt.%). The coatings were exposed to a static microindentation test, which highlighted that the pulse plated samples were more compact and less fragile than the direct current plated ones.     

Effect of the magnetic state on the damping properties of iron and nickel alloys

The dependences of the ΔEeffect and internal friction on the magnetic field have been investigated upon the magnetization and magnetization reversal of some polycrystalline ferromagnetic materials with different properties. It has been shown that for all the materials that have been investigated there is characteristic a nonmonotonic dependence of the magnitude of internal friction on the magnetic field both for the magnetization curves and for the major hysteresis loops. It is shown that in the sonic frequency range of elastic vibrations the basic mechanism of the formation of the magnetic peaks of internal friction in the materials investigated is magnetostrictive; the damping depends simultaneously on the instantaneous values of magnetostriction and magnetostrictive sensitivity.     

The use of ACORN to determine Sub-structures

Using the concepts described in the preceding paper of this volume (Foadi, J. (2003). Cryst. Rev. , 9 , 43-65) and the references therein, it has been shown that the ACORN program can position the atoms of the sub-structure of a protein using the anomalous or dispersive differences generated from these sites.     

Improvement of physical properties of Cu-infiltrated W compacts via electroless nickel plating of primary tungsten powder

In the present research, tungsten particles were coated using nickel/nickel-phosphorus electroless plating technique. The coated tungsten powders were pressed under constant pressure to achieve compact material of cylindrical shape with same porosity. Then, attained compacts were infiltrated/penetrated by liquid copper under the hydrogen atmosphere in order to obtain W-15 wt.% Cu composites. The coated/uncoated powders as well as its infiltrated compacts were characterized by optical microscopy (OM) as well as scanning electron microscopy (SEM), EDS and XRD methods. The microstructure, relative density and specific resistivity of composites were compared. The microstructural observations revealed that the infiltration behavior can be improved in the compacts prepared by both nickel and nickel-phosphorus coated tungsten powders, in comparison with uncoated ones. In addition, it was found that relative density may be raised from < 85% to > 95% by nickel electroless plating, that leads to decrease specific resistivity from 6 to 4 µΩ cm. Enhancement of electrical conductivity of infiltrated W-15 wt.% Cu compacts prepared by electroless nickel coated tungsten powders was related to its higher density.     

Influence of process parameters on electrochemical and physical properties of sputtered iron-doped nickel oxide thin films

1Introduction A principal focus of modern research in electrocatalysis is to discover electrode materials that exhibit excellent electrochemical stability and show interesting activity towards typical electrochemical reaction[1?10].It is desirable that th…     

Discrepancies in the morphology and physical properties of amorphous and crystalline sprayed lanthanum nickel oxide films

Amorphous LaNiO₃ (a-LNO) and crystalline LaNiO₃ (c-LNO) films were prepared by spraying an aqueous precursor solution of lanthanum and nickel chlorides on hot (450 °C) fused silica substrates followed by annealing at high temperatures (550–850 °C). Thermal analysis of a dried precursor indicated that a stable oxide phase is formed at 560 °C with no distinct crystallization peak. Scanning electron microscopy (SEM) powered with energy-dispersive X-ray spectroscopy (EDX) of as-sprayed films showed rough surfaces with particulate-like deposits and incomplete pyrolysis chloride composition. No chloride contents were detected in annealed films. X-ray diffraction showed that films annealed at 550 °C and 650 °C were a-LNO and those annealed at 750 °C and 850 °C were c-LNO. The c-LNO phase was indexed as a single-phase perovskite structure with (1 1 0) orientation. SEM/EDX showed that a-LNO films have rough surfaces and c-LNO films have uniform crack-free smooth surfaces. Electrical properties measurements showed that c-LNO films have lower resistivity than a-LNO films and both types of LNO films have semiconductor resistant temperature dependence. The activation energy of electric conduction of a-LNO films was found to be much higher than that of c-LNO films. The optical transmittance and reflectance of the films were studied in the UV–visible–near IR range. The optical constants were obtained by modeling the measured transmission and reflection spectra. Because of the discrepancies in the morphology and in the physical properties of a-LNO and c-LNO films, the best fit modeling of transmission and reflection spectra was obtained by using different theoretical models and different geometrical configurations. While the Drude model accounting for larger carrier density was found to be significant for c-LNO, using the Bruggmann model and a configuration of a rough layer on top of a compact film was found to be significant for a-LNO.     

Impedance spectroscopy: An efficient tool to determine the non‐steady‐state chloride diffusion coefficient in building materials

One of the most important problems of reinforced steel concrete in marine environments is the corrosion of the reinforcing bars. Most of the times, this corrosion is a consequence of the local destruction of the passive layer formed on the surface of the embedded steel, due to the arrival of chlorides present in the environment. Many efforts have been made to determine the chloride diffusion coefficient in concrete structures, both using natural diffusion methods, and accelerated migration methods. This coefficient determines the velocity of ingress of chlorides, and as a consequence the life time of the structures. In this work it is presented the possibility of using the technique of impedance spectroscopy, that is, very simple to use and requires no chemical or conductivity measurement, to determine the value of the non‐steady‐state diffusion coefficient. This technique, together with the equivalent circuits proposed for the interpretation of the measurements, allows the determination of the chloride saturation of a concrete or mortar sample. Pores of the material that are initially filled with water have high resistivity, and as the chlorides penetrate into the sample the value of the resistivity decreases. This diminution can be determined in situ, and permits the calculation of the diffusion coefficient saving experimental time and efforts. The results have been obtained both with concrete and mortar samples, and using different cement types.     

转速对高压扭转Cu试样的组织与性能的影响

通过高压扭转(HPT)技术在不同转速条件下实现了Cu试样的晶粒细化.利用光学显微镜(OM)、透射电镜(TEM)及显微硬度计观察并测试了组织的结构与性能,并基于有限元计算了变形诱导试样的温升,研究了转速对Cu试样的组织细化与性能的影响.结果表明:转速由1/3 r·min-1增大至1 r·min-1,经1圈扭转变形,试样温度由40.8℃升高到54.1℃,变形组织均为100～600 nm的高位错密度位错胞/亚晶组织,显微硬度由初始态的52HV0.05增大至140 HV0.05;经16圈扭转变形,试样温度由50.4℃升高到97.4℃,组织细化到200 nm.慢速扭转变形试样晶内位错密度高,微观组织处于严重变形状态;而快速扭转试样晶内衬度均匀,位错较少,微观组织经历明显的动态回复,显微硬度较慢速扭转变形试样低6%.