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.     

Mechanical properties of nanocrystalline nickel films deposited by pulse plating

This paper reports the mechanical properties of Ni films fabricated by pulse electrodeposition. Transmission electron microscope revealed that the prepared films had an average grain size of 25 nm with a narrow size distribution and the absence of dislocations. Small grain size leads to an increasing hardness as high as 7.8 GPa while Young's moduli keep a constant bulk value of 215 GPa, resulting in an increasing ratio of hardness (H) to elastic modulus (E). Interestingly, the wear resistance was also improved significantly. Under a constant normal load of 500 μN, the penetration depths of indenter slightly increased from 25 nm to 30 nm and the coefficient of friction varied from 0.12 to 0.20, depending on sliding scans. Depth sensing instrumented indentation experiments performed at different loading rates on specimens revealed an increasing rate-sensitivity of hardness, which concerns with a significantly small activation volume for plastic flow.     

Evolution of grain structure in nickel oxide scales

In systems such as the oxidation of nickel, in which grain-boundary diffusion in the oxide can control the rate of oxidation, understanding of the factors governing the grain structure is of importance. High-purity mechanically polished polycrystalline nickel was oxidized at 700°C, 800°C, and 1000°C for times up to 20 hr in 1 atm O₂. The scale microstructures were examined by parallel and transverse cross section transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Texture coefficients were found by X-ray diffraction (XRD). Each grain in the transverse section grain boundary networks was systematically analyzed for width parallel to the Ni-NiO interface and perpendicular length, for boundary radius of curvature and for number of sides. The variation of these parameters with depth in the scale was examined. In particular, grains were increasingly columnar (i.e., with ratio of grain length to width >1) at higher temperatures and longer times. Columnar grain boundaries tended to be fairly static; the columnar grain width was less than the rate controlling grain size predicted from the oxidation rate. The mean boundary curvature per grain provided a guide to the tendency for grain growth, except in the region of the Ni-NiO interface, where the boundaries were thought to be pinned.     

Two-phase nanostructured carbon nitride films prepared by direct current magnetron sputtering and thermal annealing

Two-phase nanocrystalline/amorphous carbon nitride films have been successfully prepared by direct current magnetron sputtering and the following thermal annealing at 1000 K. The analysis of Raman spectra supports the existence of sp³-hybridized C-N bonds in the films. The results obtained from X-ray photoelectron spectroscopy (XPS) indicate that the fractional concentration of the tetrahedral bonded crystalline phase in the carbon nitride films is 40%, and the ratio of N:C in the tetrahedral bonded crystalline phase is 1.12:1. Transmission electron microscopy (TEM) investigations indicate that the films contain a very dense and homogenous distribution of nanocrystalline grains, and the lattice parameters of these crystalline phases are in good agreement with the theoretically predicted β-C₃N₄ lattice constant. The films deposited on Si substrates have a high hardness of 40 GPa, and the correlations between the microstructure of the films and their mechanical properties are discussed.     

Regeneration and decontamination of a nickel citrate complex in spent electroless nickel plating solutions

The possibility of citrate precipitation by excess metal ions in alkaline solutions suggests the use of Ni(II) together with OH^? to precipitate a Ni(II)-citrate complex from spent electroless plating solutions. After treatment of the precipitate with acid, excess Ni(II) can be removed in the form of insoluble Ni(OH)₂. The solution of the Ni(II)-citrate complex can then be reused for electroless nickel plating. During this procedure the additive adipate is not regenerated. For decontamination of spent electroless nickel plating solutions Fe(III) can be used as Ni(II)-citrate complex precipitant.     

Effect of plating time on electrodeposition of thick nanocrystalline permalloy foils

Thick foils of nanostructured permalloy were electrodeposited by applying a current density of 100?mA?cm^?2 for 48 hours. The bath contained nickel sulphate, iron sulphate, a complex agent, a grain refiner, a stress reducing agent, a buffer and a wetting agent. The bath pH was 3·8. Different parameters were controlled to get thick (approximately 860?µm), uniform permalloy coatings. To investigate the effect of electroplating time on the surface morphology, thickness and structure of foils, scanning electron microscopy, optical microscopy and X-ray diffraction were used. Chemical compositions of foils and the bath were investigated by quantometry and ultra violet–visible spectroscopy. The composition of the coatings was constant during the long period of electroplating, which was attributed to the bath stability. The cathode current efficiency of the electroplated permalloy foils increased slightly on increasing the plating time. Existence of chloride ions, complex agent and saccharin in the bath influenced efficiency.     

Boric acid free nickel electrolyte for plating of electrical contacts

Prior to plating of electrical contacts with noble metals such as palladium or gold often an intermediate layer of nickel is applied. Owing to reasons of occupational safety and environmental protection a boric acid free nickel electrolyte for ‘High-Speed’-applications has been developed by HARTING. It was shown by examination in laboratory and pilot plant scale that the newly developed electrolyte generates layers of equal quality to layers generated with a conventional boric acid buffered Watts electrolyte. Single characteristics of the layer generated with the new electrolyte that are in particular important for connectors, e.g. corrosion and abrasion resistance, residual stress, compatibility with contaminants and buffer stability, are very good compared to those of the layers generated with the conventional Watts electrolyte.     

脉冲电沉积纳米晶体镍的耐蚀性能

采用脉冲电沉积工艺制备不同晶粒尺寸的纳米晶体镍,用浸泡法和电化学极化法研究了粗晶镍和纳米晶体镍在10%HCl溶液及20%NaOH溶液中的腐蚀行为。结果表明,在HCl溶液中,纳米晶镍的耐蚀性较粗晶镍差,随着晶粒尺寸的降低腐蚀速率升高,腐蚀过程以镍的活性溶解为主;在NaOH溶液中,纳米晶镍的耐蚀性优于粗晶镍,且随晶粒尺寸的降低腐蚀速率降低,钝化膜的存在是其耐蚀性提高的主要原因。     

Preparation of nickel nanoparticles in emulsion

The nickel nanoparticles with different sizes and spherical shape were prepared by the reduction of nickel sulfate with sodium borohydride in the water-in-oil emulsions of water/SDBS（sodium dodecylbenzene sulfonate）/n-pentanol/n-heptane. The effects of aging time, molar ratio of water to SDBS（R） and the concentration of nickel sulfate on the size of particles were studied. The samples were characterized by transmission electron microscopy（TEM） and inductively coupled plasma spectrometry（ICP）. The results show that the average particle size changes from 20 to 40 nm by adjusting aging time （15-30 min） and R （9-11.5）. The concentration of nickel sulfate of 1.0 mol/L is the favorite condition.     

High speed nickel sulphamate plating of connector strip

High deposition rates and low internal stress of the deposit from nickel sulphamate electrolytes without the use of addition agents, offset the greater cost compared to the conventional Watts nickel solution. Chloride or bromide ions can be added to the electrolyte to improve conductivity and aid dissolution of the nickel anode with little to no anode polarisation. Anodes can be either sulphur activated or pure nickel forms. These choices have been studied for a high speed nickel sulphamate solution used in reel-to-reel plating of connector strip for the electronics industry. The results provide guidance about the influence of halides and anode form on maintaining consistently low tensile stress, while presenting the opportunity for power savings and reducing the need for regular anode cleaning to remove insoluble residue from sulphur activated nickel. Over 6 years of industrial practice, pure electrolytic nickel anodes with nickel chloride added to the electrolyte have provided cost effective operating conditions combined with satisfactory deposit properties in more than 30 reel-to-reel plating lines in Asia.     

Evaluation of nanocrystalline TiN films prepared by arc ion plating

Monolayer and multilayer TiN films were synthesized on a SKD 11 steel sheet by an arc ion plating technique and the correlation between the microstructure and properties of the TiN films was comparatively investigated. The results indicated that the main phase was fcc-TiN, showing a (200) preferred orientation in the film under 2.0 × 10⁻¹ torr N₂ partial pressure, whereas a gradual transition to (111) preferred orientation was observed with decreasing N₂ partial pressure to 1.4 × 10⁻¹ torr. The (200) and (111) textures in the film under an arc current of 80 A were found to be competitive orientations, but the (200) texture became stronger as the arc current was increased. Compared to the optimal monolayer TiN films, the multilayer TiN film possessed high hardness of up to 20.3 ± 1.3 GPa and excellent wear resistance. These features are attributed to the presence of dense microstructures that are mainly composed of TiN phase and are around 1.7 μm to 1.8 μm in thickness.     

Phase field crystal simulations of nanocrystalline grain growth in two dimensions

We study two-dimensional grain growth at the nanoscale using the phase field crystal (PFC) model. Our results show that for circular grains with large misorientations the grain area decreases linearly with time, in good agreement with classical grain growth theory. For circular grains with small initial misorientations, grain rotation occurs as a result of the coupled motion between the normal motion of the grain boundary and the tangential motion of the adjacent grains. Despite this rotation and its effect on the grain boundary energy, the grain area decreases linearly with time. In addition, for intermediate initial grain misorientations, we find a repeating faceting-defaceting transition during grain shrinkage and a different relationship between the grain area and time, which suggests a different grain growth mechanism than that for small and large misorientations. For a circular grain embedded between a bicrystal with a symmetric tilt boundary, we find that the evolution of the embedded grain closely depends on dislocation reactions at triple junctions.     

镁合金在镀液中的腐蚀行为

摘要：通过腐蚀实验和阳极极化曲线研究了硫酸镍主盐配制的化学镀镍液成分和温度对AZ91D镁合金的腐蚀行为的影响，比较了碱式碳酸镍主盐和硫酸镍主盐两种镀镍液的腐蚀性以及施镀后的镀层质量。结果表明：硫酸镍镀液的腐蚀性比碱式碳酸镍镀液大，在低温下，镁合金在硫酸镍镀液中表面的氟化镁膜不致密，镀液对基材的腐蚀性高；而在高温下，Mg^2 与F^-的反应性增强，氟化反应完全，形成的氟化镁钝化膜致密性高，可保护镁合金基体免遭镀液的腐蚀。在施镀温度下，镀液中F^-的缓蚀作用，可使SO4^2-离子对镁合金的腐蚀速率大大降低。     

The growth and structure of thin oxide films on ceria-sol-coated nickel

The influence of 14-nm thick ceria ceramic coatings deposited by the sol-gel technique on the early-stage oxidation of polycrystalline nickel at 973 K was studied by analytical electron microscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry and X-ray diffraction. The size of the ceria particles in the coating was modified prior to oxidation by vacuum annealing. It was found that ceria particle size is a crucial factor affecting the oxidation kinetics, oxide microstructure, and distribution of cerium within the oxide film. Coarse ceria particles applied to the nickel surface were ineffective in the inhibition of oxidation and were spread throughout the whole oxide. Coatings with small ceria particles markedly improved the oxidation resistance. After oxidation such particles were present in the surface region of nickel oxide, acting as the sources of cerium ions segregated at the nickeloxide grain boundaries. The stereological analysis of oxide microstructure as well as microchemical examination supported the predominant role of grain-boundary segregation of cerium ions decreasing the oxidation rate. The results are discussed in terms of reactive-element effect on the development of microstructure of nickel oxide film during initial stages of oxidation.     

Cavitation erosion of electroplated nickel composite coatings

The cavitational wear resistance of electroplated nickel composite layers was tested following ASTM G32. Particles of different hardness (titania and silicon carbide) and different sizes from micro-scale to nano-scale were incorporated up to 30 vol.% into a nickel matrix. Martens hardness is improved by grain refinement via particle incorporation. Compared to pure electroplated nickel films the composite layers strengthened by submicro-scale silicon carbide particles exhibit a decreased mass loss of one order of magnitude after 8 h testing time. Remarkably, layers with nano-scaled titania particles show a similar performance.

Apart from particle adherence failures, reduced mass loss of the composite layers correlate with improved hardness of the composite due to grain refinement of the matrix and dispersion hardening effects.     

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.     

In-situ monitoring of nickel electrodeposit structure using electrochemical noise technique

The nickel electroplating process was investigated by means of electrochemical noise（EN）, cyclic voltammetry in conjunction with the scanning electron microscopy（SEM） technique. The results show that, in the experimental conditions and with the increase of current density, the growth mechanism of nickel crystallites changes from 2-D to 3-D with the potential turning point of about - 1.15 V, and the potential for the onset of diffusion control of the ensemble nickel electroplating process was about --1.4 V. In the case of activation-control, the two-dimensional （2-D） nucleation / growth process of nickel often results in the electrocrystallization EN features of only slowly small positive potential drift and the corresponding compact layer-by-layer deposit structure, and the maximum relative energy of the RP-EDP （re-plotted relative energy distribution plot）, which is obtained from wavelet analysis, defmed in the region with smaller scales. While under the diffusion-control, the three-dimensional （3-D） nucleation / growth process of nickel, often results in the electrocrystallization EN features of both the fast positive potential drift and subsequent remarkable negative potential drift and the corresponding dentritic/large conglomerate structure of nickel deposit, and the maximum relative energy of the RP-EDP defined in the region with larger scales. The electroplating time affects the nickel deposit structure mainly through its influence on the growth rate of crystallites and the Ni^2＋ ions diffusion process around each crystallite.     

Diffusion bonding of a superplastic inconel 718SPF superalloy by electroless nickel plating

Although intimate contact can be obtained for diffusion bonding of a superplastic Inconel 718SPF superalloy under a low pressure of 7 MPa, the precipitates formed at the interface retarded achievement of a sound joint. The shear strength was only 41.5 MPa for an overlap length of 12 T (T=1.3 mm, sheet thickness). The diffusion bondability of this Inconel 718SPF superalloy was enhanced by electroless nickel plating. In this situation, the bonding shear strength increased to 70.4 MPa for the same overlap length of 12 T under the same bonding condition, regardless of the roughness of the surface to be bonded. Upon decreasing the overlap length from 12 to 6 T, the bonding strength remained constant.