Zn–Fe alloy electrodeposition from chloride bath: Influence of deposition parameters on coatings morphology and structure

In this study, the kinetics of Zn–Fe codeposition was investigated in chloride acidic solution using cyclic voltammetry. Anomalous codeposition is detected and this mechanism depends on the Zn(II)/Fe(II) concentration ratio in the electrolytic bath. Influence of deposition parameters on the morphology and structure of the coatings is discussed using characterization techniques and using the anodic linear sweep voltametry (ALSV). The ratio between Zn(II)/Fe(II) considerably influences the structure of the alloys. Dense, uniform, and single‐phased Zn–Fe coatings could be obtained.     

Effect of electrolyte pH and Cu concentration on microstructure of electrodeposited Ni-Cu alloy films

Single Ni and Ni-Cu alloy films were electrodeposited on polycrystalline Ti substrates from electrolytes with different pH values under potentiostatic control. The deposition processes of the films were evaluated by the current-time transients recorded during deposition. The analysis of the transients clearly showed that the initial deposition of Ni is affected by the electrolyte pH, while in the Ni-Cu alloys the Cu concentration of the electrolyte is more effective than the electrolyte pH. The microstructural analysis by X-ray diffraction (XRD) indicated that the texture degree in both Ni and Ni-Cu alloy films, which have face-centered cubic (fcc) structure, changes with the electrolyte pH. The surface morphology of the samples was investigated using the scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was observed from SEM and AFM studies that the surface roughness of Ni deposits is not considerably affected by the electrolyte pH, while in Ni-Cu alloy films it changes significantly with both the electrolyte pH and the Cu concentration. Accordingly, the surface roughness of the Ni-Cu alloy films increased as electrolyte pH decreased and Cu concentration increased.     

The effect of current density on the grain size of electrodeposited nanocrystalline nickel coatings

The aim of this work was to investigate the effect of current density on the grain size of electrodeposited nickel coatings. For this purpose, nanocrystalline nickel coatings were deposited from a Watts bath containing 5 g/l sodium saccharin as an additive, by direct current electroplating at different current densities. X-ray diffraction analysis and modified Williamson–Hall relation were used to determine the average grains size of the coatings. The experimental results showed that the coating grains size decreased sharply by increasing the current density from 10 mA/cm² to 75 mA/cm². Nanocrystalline nickel coating with average grain size smaller than 30 nm can be achieved at the current densities higher than 50 mA/cm². Furthermore, a general and simple theoretical model based on atomistic theory of electrocrystallization has been made in order to find out the relationship between the grain size and current density. According to this model the variation of log (d) versus log (i) was linear which is in accordance with experimental results for the current densities lower than 75 mA/cm².     

The effect of saccharin addition and bath temperature on the grain size of nanocrystalline nickel coatings

Nanocrystalline nickel coating was synthesized by direct current electrodeposition from a Watts bath at the current density of 100 mA/cm² and pH = 4. The effect of saccharin addition (0-10 g/l) and bath temperature (45-65 °C) on the average grain size of the deposits was investigated by XRD technique. The results showed that the average grain size decreased from 426 nm to 25 nm as the saccharin concentration increased from 0 to 3 g/l, while further increase in saccharin concentration had no significant effect. Theoretical model also indicated a non-linear function for dependence of grain size on saccharin concentration, which was in accordance with experimental results. The experimental results showed that the increases in the bath temperature had no considerable effect on the average grain size of the deposits. A theoretical formula was also established for the temperature dependence of the grain size.     

Zinc–nickel alloy coatings electrodeposited from a chloride bath using direct and pulse current

Zinc–nickel alloys were electrodeposited on steel from chloride bath by direct and pulse current. Some electric variables (average current density, pulse frequency, duty cycle) and some important bath conditions (ratio of Ni²⁺/Zn²⁺ in bath, temperature) on chemical compositions, current efficiency, microhardness and surface appearance of coatings were studied. At low current densities, transition from anomalous to normal co-deposition was observed for both direct and pulse current. Pulse current seems to increase brightness of the coating and to decrease the precipitation of zinc hydroxide at the cathode surface. In addition, applied pulse current increases the percentage of nickel in deposits. Pulse frequency and duty cycle had little effect on the chemical composition of deposits. The polarization curve of zinc–nickel deposition with pulse current is shifted to positive potentials in comparison with direct current curves. The temperature of the plating bath had a very strong effect on the composition of the deposits. This is primarily the result of intrinsically slow nickel kinetics. The hardness of Zn–Ni alloy coatings (approx. 220 VHN) was greater than the hardness of zinc coating (approx. 161 VHN). The hydroxide suppression mechanism for Zn–Ni co-deposition has been confirmed.     

糖精钠对电沉积纳米晶镍层组织结构及性能的影响

采用脉冲电沉积法制备纳米晶镍镀层,利用扫描电镜、透射电镜及XRD对不同糖精钠浓度下制得的镍镀层的微观结构进行了表征,采用显微硬度计、DSC及全电位测试仪对镀层的硬度、热稳定性和耐蚀性进行研究.结果表明:镍镀层晶粒尺寸随着糖精钠浓度升高先增后降,浓度为10 g/L时晶粒尺寸最小;当浓度低于15 g/L时,镀层表面较为光滑、明亮;镍镀层的显微硬度在糖精钠浓度为10 g/L时达到最大值,显微硬度与平均晶粒尺寸的关系基本符合Hall-Petch方程;镍层晶粒的失稳长大温度随糖精钠浓度的增加在305℃上下波动;当糖精钠浓度为10 g/L时,镍层的耐蚀性最好.     

双向脉冲参数对金铸层的形貌和结构影响

本文采用双脉冲电沉积技术,控制单一变量,在酸性的无氰氯金酸溶液进行金的电沉积。采用扫描电子显微镜、X 射线衍射仪研究了脉冲电流密度和占空比对金铸层表面和横截面形貌,及显微结构的影响。实验结果表明正向峰值电流密度从2.25 A/dm2增加到3.75A/dm2,铸层晶粒细化,但正向电流密度过大导致表面起伏较大,铸层平整度下降;而反向峰值电流密度从6 A/dm2增加到12A/dm2时,晶粒尺寸逐渐变大,结构也变得疏松。正向占空比由20%提高到60%,会使阴极过电位增大,从而铸层晶粒细化,但是正向占空比过大会造成铸层内部出现孔隙,致密度下降;反向占空比从10%提高到40%,铸层针孔逐渐增多,变得薄脆。通过计算织构系数,可知在较高的阴极过电位下,金铸层的择优取向沿（111）和（222）晶面;低的阴极过电位下,金铸层的择优取向则沿（200）晶面。     

硫代硫酸盐无氰镀银工艺及银镀层微观组织分析

采用硫代硫酸盐无氰镀银工艺,分别以 AgNO3和 AgBr 为主盐进行镀银。研究主盐含量、电流密度对Ag镀层表面质量、沉积速率和显微硬度的影响,并优化电镀参数。分析优化工艺下的Ag镀层结合强度和晶粒尺寸。结果表明：在AgNO3体系中,AgNO3最佳用量为40 g/L,最佳电流密度为0.25 A/dm2,制备的Ag镀层光亮平整,与基体结合良好,晶粒尺寸为35 nm。在AgBr体系中的最佳AgBr用量为30 g/L,最佳电流密度为0.20 A/dm2,与基体结合良好的Ag镀层的晶粒尺寸为55 nm。与AgBr体系相比,AgNO3体系适用的电镀电流密度范围较宽,制备的Ag镀层显微硬度高,晶粒尺寸小。     

Role of deposition parameters on microstructure and mechanical properties of chromium oxide coatings

Chromium oxide coatings were deposited by reactive magnetron sputtering on high speed steel (HSS) substrate under various oxygen flow rates and radio frequency (RF) powers. The effect of deposition conditions on the microstructure, hardness and critical load of chromium oxide coating failure was studied. The results indicated that a crystalline chromium oxide coating formed at a high oxygen flow rate and a low RF power exhibited a higher hardness and a lower critical load as compared to a chromium oxide coating with an amorphous microstructure.     

Evaluation of effect of grain size on mechanical and tribological properties of pulse electrodeposited nanocrystalline nickel using nanoindentation techniques

Abstract

Pulse electrodeposition of nanocrystalline nickel has been carried out on AA 6061 substrate from a modified Watt’s bath using saccharin as a grain refining additive. By varying the concentration of saccharin and other operating parameters, nanocrystalline nickel electrodeposits of varying average grain sizes (from 115 down to 17 nm) have been obtained. Nanoindentation was employed for studying the effect of average grain size on the mechanical and tribological properties of the electrodeposits, with emphasis on hardness, elastic modulus, wear resistance and coefficient of friction. The study confirms that the hardness of nanocrystalline nickel electrodeposits increases as the average grain size decreases and a value as high as 7·2 GPa is obtained for a coating having an average grain size of 17 nm. No inverse Hall–Petch relationship is observed for the entire range of grain sizes studied. The elastic modulus of the electrodeposits remained almost constant (between 150 and 160 GPa), irrespective of the average grain size and a coefficient of friction value of 0·25 has been obtained for a deposit having an average grain size of 17 nm.     

脉冲电沉积时间对纳米晶镍镀层微观结构和性能的影响

采用脉冲电沉积法制备纳米晶镍镀层,利用扫描电镜、能谱仪、X射线衍射仪及显微硬度计对不同电沉积时间下制得的镍镀层的显微组织、微区成分、结构及力学性能进行表征分析。结果表明,不同电沉积时间下制得的镍镀层晶粒尺寸在21 nm小幅波动;随着电沉积时间的延长,纳米晶镍镀层的显微硬度存在先增大后缓慢降低的趋势,最大值为472 HV0.01,对应的电沉积时间为16 m in;纳米晶镍镀层的微观形貌为累积长大的胞状结构,电沉积时间为1~4 m in时,胞状结构表面密布着粒径为90 nm左右的二次纳米镍颗粒;本试验制得的纳米晶镍镀层失稳长大的起始温度为283.7℃,峰值温度为311.4℃。     

The deposition and recrystallization textures of copper electrodeposits obtained from a copper cyanide bath

The textures of copper electrodeposits obtained from an alkaline copper cyanide bath changed from <110> to <111> with increasing cathode current density and with decreasing bath temperature. The <111> and <110> textures of copper electrodeposits changed to the <100> and textures, respectively, when they were recrystallized. These results are similar to those in copper electrodeposits obtained from acid copper sulfate and acid copper fluoborate baths.     

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.     

电沉积参数对Co-BN（六方、）纳米复合涂层显微组织和摩擦性能的影晌

通过扫描电镜、场发射扫描电镜、能谱、原子力显微镜和X射线衍射等测试技术,研究电流密度、占空比和频率对电沉积Co—BN（六方）纳米复合涂层的显微组织和BN粒子含量的影响。同时,研究其显微硬度、摩擦性能以及磨损机理。随着电流密度和频率的增加,涂层的BN粒子含量和显微硬度先增加后减少。另外,通过减少占空比,可以沉积更多的BN粒子并且得到更高的显微硬度。在占比空10％,频率50Hz和电流密度100mA／cm2的条件下,可以得到最佳的涂层摩擦性能。     

Effect of tension deformation on microstructure and mechanism of electrodeposited nickel coating

Nickel coating deposits with better ductility on a lower carbon steel sheet were produced by electrodeposition method and the electrodeposited nickel coating was deformed with the strain of 10%. Then the surface morphology, the deformation texture and the mechanical properties were analyzed by scanning electron microscopy （SEM）, X-ray diffractometry （XRD） and nano-indentation measurement, respectively. The principle of nano-indentation to measure the hardness and elastic modulus of nickel coating was introduced. The relation curves of the load and displacement were obtained, including the original electrodeposited samples and the samples under tension. The results show that： 1） there are only two main texture components Ni （111） and Ni （200） in the nickel coating, and no new texture component is found due to the elongation; 2） after tensile deformation in the coating, the surface roughness increases and the microcrack is found; 3） The hardness and the elastic modulus decrease after tensile deformation; and 4） for the original electrodeposited sample, the indentation depths change with the load, the hardness and the elastic modulus decrease with the increase of the depth. In addition, the investigation of creep shows that the value of creep increases when the tensile strain ε〉 10%.     

激光参数对Ni基熔覆层结构及耐磨性的影响

采用热喷涂预置和激光熔覆方法在Q235钢基体上熔覆Ni基合金涂层和Ni/WC复合涂层，研究激光功率对涂层微观结构的影响。结果表明，选择合适的激光输出功率，可获得组织分布均匀、低稀释率、与基体结合良好的合金涂层；在Ni/WC复合涂层中，合理的激光功率使WC颗粒部分熔化，并在颗粒周围重新凝固并析出针状碳化物，这既有利于提高涂层的硬度又能使未熔化的WC颗粒与涂层内合金溶剂牢固结合。激光功率较大时涂层内WC颗粒烧损并沉底，沉积在涂层底部的WC颗粒，使基体到涂层的性能发生突变，这样既容易引发裂纹及疲劳破坏，又不利于涂层表面的耐磨。     

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 extrusion parameters on grain size and texture distributions of AZ31 alloy

Grain size and texture distributions have great influences on the mechanical properties of extruded rods. In order to study grain size and texture evolution during the hot extrusion process, direct extrusion tests were carried out with a variety of extrusion parameters (extrusion ratio, temperature and velocity) for commercial as-cast AZ31 magnesium alloys. Extruded specimens were investigated by optical microscopy (OM) and electron backscattered diffraction (EBSD). Experimental results show that extrusion ratio is the most important parameter for grain size refinement. Basal fiber textures with various (0 0 0 2) pole intensities are observed in extruded rods. Maximum intensities increase with the decreasing extrusion ratio and the increasing velocity, while the influence of temperature depends on the value of extrusion ratio and velocity.     

Influence of electrodeposition parameters on the deposition rate and microhardness of nanocrystalline Ni coatings

In this paper, nanocrystalline nickel (nc-Ni) coatings were prepared by a direct current electrodeposition technique. Their microstructure and microhardness were investigated by a high-resolution transmission electron microscopy and a microhardness tester. It is found that the electrodeposition parameters, including content of C₇H₄NO₃SNa?2H₂O, temperature and current density, have significant influences on the electrodeposition rate and microhardness of nc-Ni coatings. The electrodeposition rate increases with the current density stepwise. The largest electrodeposition rate is achieved at 60 °C. It decrease when the temperature is larger than 60 °C. The electrodeposition rate decreases with the increased content of C₇H₄NO₃SNa?2H₂O. The microhardnesses of the nc-Ni coatings are higher on the condition of the larger current density, lower temperature or higher content of C₇H₄NO₃SNa?2H₂O. But, it remains stable when the current density is in the range of 700-1000 A m^− 2. The relationship between the mean grain sizes and microhardness fits for the Hall-Petch function, approximately.