Ni-Co alloy coatings obtained from methanesulfonate electrolytes

It is found that codeposition of nickel and cobalt with alloy formation from methanesulfonate electrolyte occurs with predominant cobalt deposition. The crystalline alloy structure is considerably distorted as compared to pure alloy-forming metals. It is shown that a significant effect on the structure and properties of nickel-cobalt deposits is produced, apart from the alloy composition, by the current density of coating deposition. Comparison of dependences of the alloy composition on current density for methanesulfonate and sulfate electrolytes indicates a smaller change in the content of components in deposits obtained from methanesulfonate electrolyte. The observed small deviations from the constant value of the composition of the Ni-Co alloy deposited from methanesulfonate electrolyte in the current density range of 1–7 A/dm² together with large microhardness values characteristic for these coatings point to extensive prospects of application of methanesulfonate electrolytes for deposition of nickel-cobalt alloys.     

Pulse plating of Pd-Ni alloys: Dependence on current density

Pulsed-current electrolysis with the ratio of on-time to off-time of 1:99 has been applied to the deposition of Pd-Ni alloys from a palladium ammine chloride-nickel sulphate bath.The change in the metal ratio of the alloy deposits with an increase in the average current density was less pronounced using the application of pulsed-current electrolysis with extremely short on-time, 0.1 ms. The dependence of the hydrogen content of the Pd-Ni alloys in the current density was also smaller in deposits obtained by the pulsed-current electrolysis with shorter on-time. Even though current density was appreciable, extremely short on-time and much longer off-time brought about no diffusion polarization. The factor affecting the composition of the Pd-Ni alloy deposits (metal ratio and hydrogen content of the films) seemed to be the concentration of the depositable ions in the vicinity of the electrode surface.The preferred orientation of the Pd-Ni alloys deposited by pulsed current changed in the order (111) → (100) → (110) with increase in the current density. The energy required for two-dimensional nucleation on metals with the f.c.c. lattice has been known to increase in the same order. In a similar manner to the deposition of the single metal, an increase in the average current density in the alloy deposition led to a high overpotential and produced fine-grained deposits. The structural features of the Pd-Ni alloy deposits such as the preferred orientation and the grain size seemed to depend on the amount of energy supplied for the crystallization process of the metals.     

Electrolytic Codeposition of Nickel and Phosphorus from Methanesulfonate Electrolyte

The characteristics of Ni–P alloy electrodeposition from a methanesulfonate electrolyte have been investigated. It has been found that the phosphorus content of the alloy increases with increasing the concentration of sodium hypophosphite in the electrolyte and reducing the electrodeposition current density. A mechanism of codeposition of nickel and phosphorus has been suggested. It is shown that phosphorus was formed by electrochemical reduction of hypophosphite anions and their disproportionation at a catalytically active surface of a nickel cathode. It has been shown quantitatively that the most likely path for the formation of phosphorus through the electrochemical mechanism is the direct electrochemical reduction of a hypophosphite anion to atomic phosphorus. The rate of phosphorous formation from hypophosphite anions is dependent on the concentration of hydrogen ions in the near-electrode layer. Therefore, the phosphorus content of the coatings obtained from the methanesulfonate electrolyte is slightly decreased as compared with that from the sulfate electrolyte which exhibits higher buffering properties. It has been revealed that codeposition of nickel and phosphorus reduces the kinetic difficulties of electrochemical reduction of the nickel ions. This might be due to an increased near-electrode concentration of nickel hydroxyl complexes discharging at the cathode, which is the result of an increased near-electrode pH caused by the reactions involving hypophosphite anions and hydrogen ions.     

Studies on electrochemical deposition of novel Zn–Mn–Ni ternary alloys from an ionic liquid based on choline chloride

Ternary Zn–Mn–Ni alloy coatings were electrodeposited for the first time from a choline chloride based ionic liquid with the aim of collecting properties of binary Zn–Mn and Zn–Ni alloys into one alloy system. The effect of electrodeposition potential on the composition and corrosion performance of the obtained ternary Zn–Mn–Ni deposits was investigated and contrasted with the characteristics of Zn–Mn and Zn–Ni deposits. Cyclic voltammetry revealed that the deposition of ternary Zn–Mn–Ni alloys behaved differently from the deposition of binary Zn–Mn and Zn–Sn alloys and that Mn deposition takes place at positive potentials in the Zn–Mn–Ni electrolyte than in the Zn–Mn electrolyte due to the presence of Ni²⁺ ions in the electrolyte. X-ray diffraction studies showed that the Zn–Mn–Ni ternary alloys consist of a lattice of Zn (with Mn and Ni imbedded inside) at low electrodeposition potentials and MnZn(with Ni imbedded inside) phase at high electrodeposition potentials. Chemical composition analysis show that the Mn content in the ternary Zn–Mn–Ni alloy increased with increase in electrodeposition potential, whereas Zn and Ni contents are suppressed. The corrosion tests results indicate that through addition of Ni into the Zn–Mn binary alloy, the Zn–Mn–Ni alloy tailored are more corrosion resistant than the Zn–Mn binary alloy whilst the passivation behavior is still preserved.     

Electrodeposition of lead–tin alloy from methanesulphonate bath containing organic surfactants

The article discusses the process of electrodeposition of lead-tin alloy (tin content in the deposit up to 10–12 wt %) from methanesulfonate electrolytes. A composition was proposed of organic additives to the electrolyte providing attainment of high quality microcrystalline coatings with the alloy of predetermined composition at relatively low content of Sn²⁺ in the solution. It has been shown that the tin content in the deposit increases at an increase in current density and decrease in the electrolyte temperature. For production of anti-frictional Pb-Sn alloys with the tin content of about 10% the electrolysis should be performed at a current density of about 4 A/dm² and the temperature not exceeding 25°C. The effect of a decrease in the discharge rate of the Sn²⁺ ions into the alloy at deposition from electrolyte without organic additives was discovered, that is stipulated by deceleration of crystallization stage of tin on foreign substrate. When the alloy is deposited from electrolyte containing a composition of organic additives, the effect of super-polarization of discharge of Sn²⁺ ions is reduced.     

Studies on the Mechanism,Structure and Microhardness of Ni-W Alloy Electrodeposits

The electrodeposition of Ni-W alloy has been studied on the glassy carbon electrode by the cyclic voltammetry and potentiostatic step methods. It has been found that electrodeposition of Ni-W alloy involves an intermediate valence tungsten oxide which inhibits hydrogen evolution. Ni-W alloy electrodeposition occurs by a mechanism involving progressive nucleation followed by three dimensional growth.

The structures of nickel-tungsten alloy deposits were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD results from Ni-W alloy deposits reveal a face-centered cubic solid solution, the microstructure of the deposits exhibit (111) preferred orientation. The lattice constant and microhardness of Ni-W alloy deposit increase as the tungsten content increases, the XPS results of Ni-W alloy deposits indicate that the nickel and tungsten of the deposits exist in the metallic state, but the Ni-W alloy deposit with a tungsten content of 40.7% is an intermetallic compound. The XPS results of the deposit with tungsten content of 40.7% show that the atomic ratio of Ni to W is 4:1, so β-Ni₄ W alloy can be obtained by electrodeposition and its microhardness (Hv) is as high as 672.8.     

镀液组成和工艺条件对电沉积钴钨合金成分的影响

研究了镀液中钨盐浓度，络合剂浓度，钠离子，电流密度，镀液温度等对电沉积钴钨合金成份的影响，结果表明：合金中的钨含量随钨盐浓度，电流密度和温度的升高而增大，随络合剂，钠离子浓度的升高而降低。     

微观相场法计算Fe含量对NiAlFe三元合金中反位缺陷的影响

采用三元微观相场模型,对铝含量大于25%(原子分数,下同)与镍含量大于75%(原子分数,下同)的NiAlFe三元合金中反位缺陷NiAl、AlNi随Fe含量变化的规律进行模拟计算,其中NiAl(AlNi)表示Ni(Al)原子占据Al(Ni)格点产生的反位缺陷。结果表明:在一定温度范围内,随着Fe含量的增大,铝含量大于25%的NiAlFe合金中AlNi浓度明显上升,NiAl浓度略有上升,但小于AlNi浓度,相反在镍含量大于75%的NiAlFe合金中NiAl浓度明显上升且远大于AlNi浓度;同一温度下比较铝含量大于25%与镍含量大于75%的NiAlFe合金中反位缺陷受Fe含量影响的程度差异,发现前者的AlNi浓度比后者受Fe含量影响大,而后者的NiAl浓度比前者受Fe含量影响大。此外,反位缺陷NiAl和AlNi浓度随时间的演化规律均是逐渐由初始值降低至平衡值;温度升高促使反位缺陷演化变缓慢以及平衡时浓度增大。     

退火温度对挤压态细晶钨合金性能及组织演变的影响

采用稀土微合金化和液相强化烧结技术制备细晶93W-4.9Ni-2.1Fe+0.03%Y合金。研究在快速热挤压形变强化后,时效热处理对挤压态细晶93W-4.9Ni-2.1Fe+0.03%Y合金显微硬度和组织演变的影响,并与相应条件的传统钨合金进行对比。结果表明,随着退火温度的升高,2种钨合金钨相的显微硬度大大降低。EDS分析表明,随着退火温度的升高,钨合金粘结相中钨含量逐渐增加,其中细晶钨合金经过1200 ℃退火处理后,粘结相钨含量高达26.11%,而传统钨合金在1350 ℃退火处理后含量最高,达到28.14%。显微组织观察表明,退火有利于降低W-W连接度和细化钨颗粒;与传统钨合金相比,高温退火后,细晶钨合金的粘结相体积比更高且分布更为均匀     

纳米钨合金粉末的制备技术

钨合金包括W－Ni-Fe,W-Ni-Cu,W-Cu,WC-Co等钨基合金材料。钨合金材料将是21世纪出现的一种多功能高性能的多胜任的新型材料。有杉纳米粉末制备的亚微或微米钨合金块体材料具有非常优越的潜在物理力学性能,用作高性能结构件和高性能电子、微电子等功能材料方面都将具有很大的潜在优势,可以更好地满足高性能新型材料的要求。本文综合近几年来国内外纳米钨合金的研究状况,详细地介绍了有关纳米钨合金粉末的制备技术,预测了今后钨合金材料的研究方向。     

Anodic oxidation of Ta/Fe alloys

The behaviour of iron during anodizing of sputter-deposited Ta/Fe alloys in ammonium pentaborate electrolyte has been examined by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. Anodic films on Ta/1.5 at.% Fe, Ta/3 at.% Fe and Ta/7 at.% Fe alloys are amorphous and featureless and develop at high current efficiency with respective formation ratios of 1.67, 1.60 and 1.55 nm V⁻¹. Anodic oxidation of the alloys proceeds without significant enrichment of iron in the alloy in the vicinity of the alloy/film interface and without oxygen generation during film growth, unlike the behaviour of Al/Fe alloys containing similar concentrations of iron. The higher migration rate of iron species relative to that of tantalum ions leads to the formation of an outer iron-rich layer at the film surface.     

Effects of saccharin and cobalt concentration in electrolytic solution on microhardness of nanocrystalline Ni-Co alloys

Cobalt content, surface morphology and microhardness of nanocrystalline Ni-Co deposits prepared by pulse plating technique at constant electrodeposition conditions with varied concentration of saccharin and cobalt sulfate in the electrolyte were investigated. It is found that appropriate amount of both additions could lead to finer structure and higher hardness of the deposit and further increase of the concentration could result in decline of the hardness, which is regarded as the result of inverse Hall-Petch relation. The maximum hardness of the Ni-Co alloy deposits is not higher than that of their pure Ni counterparts, indicating that the refinement hardening effect (Hall-Petch relation) is dominant in nanocrystalline Ni-Co alloy deposits. By adding Co ions to the electrolyte, the amount of organic refiner saccharin (responsible for introduction of sulfur and carbon impurities) needed to produce nanocrystalline deposits could be remarkably reduced.     

Electrochemical behavior of cobalt and electroplating of cobalt-molybdenum (tungsten) alloys from oxide melts

Electrochemical behavior of cobalt in a tungstate melt, as well as the effect of electrolysis conditions on the composition and structure of cobalt-molybdenum (tungsten) alloy deposits from tungstate-molybdate melts is studied. With a decrease in the concentration of cobalt and an increase in the concentration of molybdenum (tungsten) in the melt, the phase composition of cathodic deposits is shown to change from individual cobalt to individual molybdenum (tungsten) via a series of cobalt-molybdenum (tungsten) alloys of various compositions. Original Russian Text ? V.V. Malyshev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 6, pp. 607–612.     

Effect of tungsten content on microstructure and quasi-static tensile fracture characteristics of rapidly hot-extruded W-Ni-Fe alloys

Tungsten heavy alloys (WHAs) with three different compositions (90W-7Ni-3Fe, 93W-4.9Ni-2.1Fe and 95W-3.5Ni-1.5Fe, wt.%) were heavily deformed by one-pass rapid hot extrusion at 1100 °C with an extrusion speed of ~ 100 mm/s and an extrusion ratio of ~ 3.33:1. The influence of tungsten content on the microstructure and tensile fracture characteristics of the as-extruded alloys was investigated in detail. The results show that the tungsten particles in the as-extruded 95W have the largest shape factor compared to the as-extruded 90W and 93W alloys and this implies that the tungsten particles in the as-extruded 95W alloy were subjected to the heaviest plastic deformation. In addition, ultimate tensile strength (UTS) and hardness (HRC) are significantly improved after rapid hot extrusion. The as-extruded 95W alloy processes the highest strength (1455 MPa) and hardness (HRC40) but the lowest elongation (5%), followed by the as-extruded 93W (UTS1390MPa; HRC39; 7%) and 90W alloys (UTS1260MPa; HRC36; 10%). The fracture morphology shows the distinct fracture features between the as-sintered alloys and the as-extruded alloys. For the as-sintered alloys, the fracture modes are various while transgranular cleavage of tungsten particles is the main characteristic in the as-extruded alloy. Meanwhile, the fracture modes of the three as-extruded alloys vary slightly with the tungsten content. TEM bright field images indicate that many lath-like subgrains with the width of 150-500 nm are present in the three as-extruded alloys, particularly in the as-extruded 93W and 95W alloys. Furthermore, the dislocations are absent in the γ-(Ni, Fe) phase. This means that dynamic recovery-recrystallization process took place during rapid hot extrusion.     

Microstructural control of and mechanical properties of mechanically alloyed tungsten heavy alloys

93W-5.6Ni-l.4Fe tungsten heavy alloys with controlled microstructures were fabricated by mechanically alloying of elemental powders of tungsten, nickel and iron by two different process routes. One was the full mechanical alloying of blended powders with a composition of 93W-5.6Ni-l.4Fe, and the other was the partial mechanical alloying of blended powders with a composition of 30W-56Ni-14Fe followed by blending with tungsten powders to form a final composition of 93W-5.6Ni-l.4Fe. The raw powders were consolidated by die compaction followed by solid state sintering at 1300°C for 1 hour in a hydrogen atmosphere. The solid state sintered tungsten heavy alloys were subsequently liquid phase sintered at 1445∼1485°C for 4-90 min. The two-step sintered tungsten heavy alloy using mechanically alloyed 93W-5.6Ni-l.4Fe powders showed tungsten particles of about 6-15 μm much finer than those of 40 um in a conventional liquid phase sintered tungsten heavy alloy. An inhomogeneous distribution of the solid solution matrix phase was obtained in the two-step sintered tungsten heavy alloy using partially mechanically alloyed powders. The two-step sintered tungsten heavy alloy using mechanically alloyed 93W-5.6Ni-l.4Fe powders showed larger elongation of 16% than that of 1% in the solid state sintered tungsten heavy alloy due to the increase in matrix volume fraction and decrease in W/W contiguity. Dynamic torsional tests of the two-step sintered tungsten heavy alloys showed reduced shear strain at maximum shear stress than did the sintered tungsten heavy alloys using the conventional liquid phase sintering.     

Electrochemical behavior of copper-nickel alloys in acidic chloride solutions

The electrochemical behavior of Cu-Ni alloys in acidic chloride medium was investigated. Commercial Cu-Ni alloys were investigated using potentiodynamic techniques, complemented by electrochemical impedance spectroscopy. The influence of alloy composition, chloride ion concentration and immersion time on the electrochemical response of the alloys was analyzed. Results of present investigations with pure metals (Cu and Ni) are also considered in this paper for the sake of comparison. Potentiodynamic measurements reveal that the increase in nickel content decreases the corrosion rate of the alloy and when the nickel content exceeds 30%, an increase in the corrosion rate was recorded. Also, the corrosion current density increases with increasing the concentration of chloride ions up to 0.6 M.The experimental impedance data were fitted to an equivalent circuit model representing the electrode/electrolyte interface. The relevance of the proposed model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.     

Electrodeposition of Zn-Co and Zn-Co-Fe alloys from acidic chloride electrolytes

The electrodeposition operating conditions for Zn-Co and Zn-Co-Fe alloys from chloride baths were studied. The electrodeposition was performed on a high strength steel substrate, under galvanostatic conditions, for a range of current densities at varying Co²⁺ and Fe²⁺ bath concentrations and at different temperatures. A transition current density was noticed above which a transition from normal to anomalous deposition took place. Below the transition current density electrodeposition of alloys with a higher amount of Co was obtained. Above the transition current density (i.e. in the anomalous range), both Zn-Co and Zn-Co-Fe alloys were deposited with a Co content lower than the composition reference line. This transition current density that resulted in normal to anomalous deposition was attributed to the shift in cathodic potential or polarization. However, it was found that under certain conditions the transition occurred from very high wt.% Co to almost equal to the amount of Co in the electrolyte. The increase of Fe²⁺ ions in the electrolyte assisted in increasing the Co content and decreasing the Zn content in the deposits. In addition, the increase of Fe²⁺ resulted in shifting the transition current density to a lower value. However, the cathodic current efficiency decreased with the addition of Fe²⁺ ions in the electrolyte.     

电铸制备Ni-Fe合金的居里温度研究

磁性材料因其居里温度特征而可以用来感知周围温度并应用于控制或报警。采用电铸工艺制备了Ni-Fe合金磁性材料,对其成分和居里温度进行了测试。结果表明,电铸Ni-Fe合金中的Fe的质量分数随电解液中硫酸亚铁浓度的增加而增加;依电铸Ni-Fe合金中Fe的质量分数的高低,其磁热重曲线呈现两种不同的形式;Fe的质量分数在0~70%的范围内增加,电铸Ni-Fe合金的居里温度先上升后下降,居里温度值约在358~633℃的范围内。     

A Study into the Electrodeposition Mechanisms of Zinc-Nickel Alloys from an Acid-Sulphate Bath

Zinc-nickel alloys were electrodeposited under galvanostatic conditions from a sulphate based electrolyte. The effect of deposition current density on alloy composition was determined for an electrolyte containing 0.58 mol/l nickel and 0.92 mol/l zinc (as sulphates). At current densities exceeding 0.01 A/dm², a transition from normal deposition to anomalous co-deposition (ie where the less noble metal deposits preferentially) was observed and alloys rich in zinc were obtained. The transition current density was observed to increase with an increase in electrolyte temperature or a decrease in electrolyte pH.

The electrodeposition mechanism for zinc-nickel alloys in the transition regions was studied in detail using potentiodynamic cathodic polarisation techniques. The results were consistent with the suppression of nickel deposition due to the precipitation of zinc hydroxide on the cathode surface. This was supported by pH measurements made in the vicinity of the cathode where a rise in pH was detected as the transition current density was approached and exceeded the critical pH for zinc hydroxide precipitation.     

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.