Microstructure and depositional mechanism of Ni-P coatings with nano-ceria particles by pulse electrodeposition

Nano-CeO2 （RE） particles were co-deposited into Ni-P binary composite coatings by applying pulse current （PC） under ultrasonic （U） field. Morphology, chemical content and crystal microstructure were characterized by environmental scanning electron microscopy （E-SEM） with energy dispersive X-ray analysis （EDXA）, XRD diffractometry and transmission electron microscopy （TEM）. Experimental results show that Ni-P coating reinforced with 15g/L nano-CeO2, in amorphous state and with compact structure, can be improved in the microhardness from HV0.2580 to HV0.2780 by annealing at 600 °C for 2 h. The highest content of codeposited Ce and deposition rate can reach 2.3% and 68 μm/h, respectively. Furthermore, the effect of RE adsorption and pulse overpotential on depositional mechanism was investigated. n-CeO2 particles or Ce4＋ ions with strong adsorption capacity acted as the catalytic nucleus to improve densification effectively. During annealing at 600 °C for 2 h, n-CeO2 particles will uniformly adsorb on crystal grain to preferentially pad and heal up gaps of cracking Ni boundaries, promoting dispersion strengthening with refiner-grained structure.

Microstructure and properties of nanocrystalline nickel coatings prepared by pulse jet electrodeposition

The fabrication of nanocrystalline nickel coatings was conducted by pulse jet electrodeposition on the substrate of 45# carbon steel.The effects of average current density on the surface morphology,microstructure,average grain size and microhardness of nickel coatings were investigated by scanning electron microscopy(SEM),X-ray diffractometry(XRD)and microhardness measurement.In addition,the corrosion resistances of coating and substrate were compared.It is revealed that the nickel coatings prepared by pulse jet electrodeposition exhibit a fine-grained structure with a smooth surface and a high density,although some pores and defects are still present in coatings.With the increase of average current density,the average grain size of nickel coatings is reduced at first and then increased.The coating with the optimum compactness,the smallest average grain size(13.7 nm)and the highest microhardness are obtained at current density of 39.8 A/dm2.The corrosion resistance is obviously increased for the coatings prepared by pulse jet electrodeposition;however,the corrosion rate is increased after a certain period due to the penetration of the corrosive media.

Novel Nanostructured MnO_2 Prepared by Pulse Electrodeposition:Characterization and Electrokinetics

Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample （pcMD） were carried out by different techniques： Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, Raman spectroscopy, and atomic force microscopy （AFM）. SEM image revealed that pulse current could improve the current distribution. This was confirmed by AFM images showing a decrease in surface roughness of pcMDs in comparison to amorphous samples, which were deposited by direct current （dcMD）. Higher distortion of MnO6 octahedral environment of dcMD was detected by FTJR and Raman spectroscopy. Cyclic voltammetric （CV） measurements showed a generally higher energy level drained from the second electron discharge of pcMD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcMD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcMD grains.

Electrodeposition and characterization of nanocrystalline Fe-Ni-Cr alloy coatings synthesized via pulse current method

The nanocrystalline Fe-Ni-Cr coatings were electrodeposited by using the pulse current technique.The SEM results showed that the coatings had a mixed morphology of small nodules and fine cauliflower structures at low current densities.Also,the Cr content was increased at expense of Fe and Ni contents at high current densities.XRD patterns confirmed that the pulse current density had a positive effect on the grain refinement.The results of vibrating sample magnetometer(VSM)measurements demonstrated that by increasing the current density,the saturation magnetization was decreased and the coercivity was increased due to the enhancement of Cr content and the reduction of the grain size.The friction coefficient and wear rate values were decreased by increasing the pulse current density.Also,both the adhesive and abrasive wear mechanisms were observed on the worn surfaces.The abrasive grooves and the amount of wear debris were decreased by increasing the pulse current density.

Effect of bath composition and pulse electrodeposition condition on characteristics and microhardness of cobalt coatings

Nanocrystalline cobalt coatings were produced from cobalt sulfate based electrolytes by using pulse current electrodeposition technique.The effects of bath composition and electrodeposition condition on current efficiency,morphology,structure and hardness of the coatings were investigated and the optimum deposition condition was determined.It was found that increment of cobalt sulfate concentration and sodium dodecyl sulfate(SDS)concentration in the bath had a negligible effect on microhardness of the coatings,while they were effective on electrodeposition current efficiency.Adding saccharin to electrodeposition bath decreased crystallite size of hexagonal close-packed(hcp)cobalt films and increased their microhardness without significant effect on current efficiency.Smoother and less defective coatings were also obtained from baths containing SDS and saccharin.The results revealed that both the current efficiency and microhardness were changed by variation of peak current density and duty cycle.Besides change of smooth morphology of the coatings to needle-shaped one,crystallite sizes and preferred orientation also varied with increasing the current density and duty cycle.

Influence of SiO_2 nano-particles on microstructures and properties of Ni-W-P/CeO_2-SiO_2 composites prepared by pulse electrodeposition

Ni-W-P base composites containing CeO2 and SiO2 nano-particles were prepared on common carbon steel surface by pulse co-deposition of Ni,W,P,CeO2 and SiO2 nano-particles.The influence of SiO2 concentrations in bath on microstructures and properties of Ni-W-P/CeO2-SiO2 composites was studied,and the characteristics were assessed by chemical compositions,element distribution,surface morphologies,deposition rate and microhardness.The results indicate that when SiO2 concentration in bath is controlled at 20 g/L,the composites possess the fastest deposition rate,the highest microhardness,compact microstructures,smaller crystallite sizes and uniform distribution of W,P,Ce and Si within Ni-W-P matrix metal.Increasing SiO2 concentration in bath from 10 to 20 g/L leads to the refinement in grain size and the inhomogeneity of microstructures.While when SiO2 concentration is increased to 30 g/L,the crystallite sizes increase again and some bosses with nodulation shape appear on the surface of composites.

In vitro biodegradability and biocompatibility of porous Mg-Zn scaffolds coated with nano hydroxyapatite via pulse electrodeposition

The biodegradability and biocompatibility of porous Mg-2Zn（mass fraction, %） scaffolds coated with nano hydroxyapatite（HAP） were investigated. The nano HAP coating on Mg-2Zn scaffolds was prepared by the pulse electrodeposition method. The as-deposited scaffolds were then post-treated with alkaline solution to improve the biodegradation behavior and biocompatibility for implant applications. The microstructure and composition of scaffold and nano HAP coating, as well as their degradation and cytotoxicity behavior in simulated body fluid（SBF） were investigated. The post-treated coating is composed of needle-like HAP with the diameter less than 100 nm developed almost perpendicularly to the substrate, which exhibits a similar composition to natural bone. It is found that the products of immersion in SBF are identified to be HAP,（Ca,Mg）3（PO4）2 and Mg（OH）2. The bioactivity, biocompatibility and cell viabilities for the as-coated and post-treated scaffold extracts are higher than those for the uncoated scaffold. MG63 cells are found to adhere and proliferate on the surface of the as-coated and post-treated scaffolds, making it a promising choice for medical application. The results show that the pulse electrodeposition of nano HAP coating and alkaline treatment is a useful approach to improve the biodegradability and bioactivity of porous Mg-Zn scaffolds.

Study on the Structures and Properties of Ni-W-B-CeO_2 Composite Coatings Prepared by Pulse Electrodeposition

The aim of this research is to pulse co-deposit nano-CeO2 particles into Ni-W-B alloy coatings in order to improve the surface properties. The influence of pulse frequency and duty circle on deposition rate, microhardness and microstructures, and the influence of heat treatment temperature on phase structures, microhardness and abrasivity of Ni-W-B-CeO2 composite coatings were investigated. The results indicated that the pulse co-deposition of nickel, tungsten, boron and nano-CeO2 particle from the bath which nano-CeO2 particle was suspended by high speed mechanical stirring led to the Ni-W-B-CeO2 composite coatings, possessing better microhardness and abrasion resistance when heat-treated at 400 ℃ for 1 h. The microhardness as-deposited with 636 Hz and the deposition rate with 0.0281 mm·h-1 was the highest at pulse frequency with 1000 Hz and pulse duty circle with 10%. Microstructures analysis displays that decreasing pulse duty cycle leads to refinement in grain structures and the improvement of microstructures. X-ray diffraction shows that the composite coating as-deposited was mainly in the amorphous state and partially crystallized, but when heat treated at 400 ℃, the crystallization trend was strengthened further.

Effect of Rare Earth on Microstructure and Corrosion Resistance of Pulse Reversal Current Electrodeposition Ni-Co Alloy Coatings

The effect of adding RE to plating bath on microstructure and corrosion resistance of Ni-Co alloy coatings prepared by pulse reversal current electrodeposition was studied by means of SEM/EDS, electrochemical analysis and corrosion mass loss etc. The results show that adding proper RE to plating solution can promote the microstructure of coatings compacter, the surface smoother and the crystal finer, and improve the corrosion resistance. The coatings exhibite the highest corrosion resistance when the concentration of RE reaches 0.25 g·L -1. The reason of increasing corrosion resistance by adding RE was also investigated.

Electrodeposition of Gold to Conformally Fill High-Aspect-Ratio Nanometric Silicon Grating Trenches: A Comparison of Pulsed and Direct Current Protocols

Filling high-aspect-ratio trenches with gold is a frequent requirement in the fabrication of X-ray optics as well as micro-electronic components and other fabrication processes. Conformal electrodeposition of gold in sub-micron-width silicon trenches with an aspect ratio greater than 35 over a grating area of several square centimeters is challenging and has not been described in the literature previously. A comparison of pulsed plating and constant current plating led to a gold electroplating protocol that reliably filled trenches for such structures.

Pulsed electrodeposition of hydroxyapatite on titanium substrate in solution containing hydrogen peroxide

Hydroxyapatite(HAP) coatings were prepared on the titanium substrate in the electrolyte containing H2O2 by the pulse electrodeposition. The introduction of H2O2 restrains the evolution of H2 and improves the adhesive strength between coatings and substrate. The results of pulse electrodeposition show that the relaxation time of the pulse is beneficial to growth of HAP because it makes ions diffuse from bulk to the surface of electrode and reduces concentration polarization in the next pulse time. It is beneficial to the increase of the duty circle of the pulse for deposition of HAP, but the result is not good if it is increased excessively. With increasing potential, it is good for the growth of HAP coatings. If the potential is too high, it is easy for HAP coatings to drop off during the process of electrodeposition under too intensive polarization, such as -1.0 V (vs SCE), and there is not many coatings on the substrate. The combination of pulse electrodeposition and addition of hydrogen peroxide can assuredly improve the physico-chemical properties of hydroxyapatite coatings.

Pulse Electrodeposition and Nanoindentation Test of ZrO_2/Ni Nanocomposite

ZrO2/Ni nanocomposite was produced via pulse electrodeposition using a nickel sulfmate bath. The effects of main factors including pH value, temperature T, current density Dk and ZrO2 content p on the electrodeposit were dealt with by the Taguchi method. Experimental results show that the current density and ZrO2 content affect the electrodepositing process significantly. Nanocomposite with an average grain size of about 50 nm and ZrO2 content of up to 0.4 wt% was produced under the optimal condition. The Young＇s modulus of the achieved composite is similar to that of polycrystalline Ni. The microhardness is much higher than that of common pure Ni, primarily due to the ultrafine grains of Ni matrix by the Hall-Petch mechanism. The homogeneous dispersion of stiff ZrO2 particles in the Ni matrix acting as dislocation pinning and microcrack pinning also results in the strengthening effect.

Process of pulse electrodeposition nanocrystalline chromium from trivalent chromium bath

Nanocrystalline chromium coating was prepared by pulse electrodeposition from trivalent chromium bath containing carboxylate-urea as complexing agent. The effects of electrodeposition parameters such as current density,bath temperature and solution concentration on the thickness and electrodeposition velocity of Cr deposited films were investigated. The crystallographic structures,morphology and chemical composition of Cr deposited films were analyzed by means of XRD,SEM and EDS. The results indicate that the deposited films with thickness up to 11.2 μm possess a smooth and clean appearance,and the grain size is less than 100 nm. The coating is pure chromium and the Cr deposit has face-centered cubic(fcc) structure and exhibits a(210) growth preference. Both the electrodeposition velocity and thickness exist maximum under different concentration complex agents,ureas,acetates,different temperatures and current densities. Compared with direct current electrodeposition,the thicker coating and finer grains can be obtained at lower temperature and current density by pulse electrodeposition. The electrodepostion velocity is about 0.24 μm/min,which is faster than that by direct current electrodeposition. In 1 mol/L H2SO4,3.5% NaCl and 10% NaOH solution,corrosion potential of Cr pulse-deposited film is about 100 mV higher than that of direct current. Corrosion and passivation current densities are lower and the nanocrystalline exhibits better corrosion resistance.

Pulse-plating electrodeposition and annealing treatment of CuInSe_2 films

CuInSe2 (CIS) thin film was prepared on molybdenum substrate using pulse-plating electrodeposition in aqueous solution. The most suitable pulse potential range for co-deposition is found to be from -0.55 to -0.75 V (vs SCE) from linear potential scanning curve. The electrodeposited films were characterized by X-ray diffractometry (XRD), scanning electron microscopy(SEM) and energy dispersive X-ray analysis (EDS). The annealing effects on electrodeposited precursors were investigated. And the influence of pulse parameters on film quality was studied. The chalcopyrite phase CuInSe2 films with smooth surface and stoichiometric composition are obtained at a pulse potential from -0.65 to -0.7 V (vs SCE), a pulse period of 1-9 ms with a duty cycle of 33% and annealing treatment.

Effects of pulse current on properties of electrodeposited RE-Ni-W-P-SiC composite coating

Effects of pulse current on properties of electrodeposited RE-Ni-W-P-SiC composite coating were studied. The results show that hardness of the pulse current electrodeposited composite coatings is higher than that of the direct current electrodeposited composite coatings while other parameters are the same. Otherwise, the deposited velocity is higher, and wear resistance and corrosion resistance of the pulse current electrodeposited composite coatings are also improved when the average current density is 10 A/dm2 , pulse frequency is 800 Hz and duty ratio is 1: 5. The hardness of the coating as-deposited is HV500 - 700, and it reaches HV1300 after heat treatment at 400 ℃ for 1 h.

Composition and Morphology of Zn-Co Alloy Coatings Deposited by Means of Pulse Plating Containing Reverse Current

The influence of bath constituents and pulse parameters on cobalt content, surface morphologies and grain size of Zn-Co alloy deposits was studied using a pulse plating technique with a square- wave current containing reverse pulse, It is found that Zn-Co alloy coatings obtained from the bath with the cobalt ion concentration over 60 wt% have a higher cobalt content in deposits. The results of pulse plating show that the average current density and reverse anodic current density amongst the variables investigated have very strong effects on the cobalt content in the Zn-Co alloy deposits. It is possible to electrodeposit Zn-Co alloy coatings with 10-90 wt% cobalt by modulating pulse parameters. The grain size, surface appearance and internal stress in the deposit were improved significantly by introducing the reverse current.

Microstructure,tribological behavior and magnetic properties of Fe−Ni−TiO_(2) composite coatings synthesized via pulse frequency variation

The Fe−Ni−TiO_(2) nanocomposite coatings were electrodeposited by pulse frequency variation.The results showed that the nanocomposite with a very dense coating surface and a nanocrystalline structure was produced at higher frequencies.By increasing the pulse frequency from 10 to 500 Hz,the iron and TiO_(2) nanoparticles contents were increased in expense of nickel content.XRD patterns showed that by increasing the frequency to 500 Hz,an enhancement of BCC phase was observed and the grain size of deposits was reduced to 35 nm.The microhardness and the surface roughness were increased to 647 HV and 125 nm at 500 Hz due to the grain size reduction and higher incorporation of TiO_(2) nanoparticles into the Fe−Ni matrix(5.13 wt.%).Moreover,the friction coefficient and wear rate values were decreased by increasing the pulse frequency;while the saturation magnetization and coercivity values of the composite deposits were increased.

Pulse Plating of Zn-Co Alloy Coatings

Pulse plating of Zn-Co alloys was studied using square pulse containing reverse current.The surface morphologies of Zn-Co alloy deposits were examined using scanning elecron microscopy （SEM）, and an attendant energy dispersive X-ray analyzer （EDA） was used to analyze the composition of Zn-Co alloy deposits. Results obtained showed that the average current density and reverse current density amongst all the variables investigated had very strong effects on the cobalt content and surface morphologies of Zn-Co alloy deposits. It is possible to elecrodeposit Zn-Co alloy coatings with a very wide cobalt content range of 10-90 wt% by modulating pulse parameters.

Effect of Duty Cycle on Properties of Pulse-electro-deposited SnS:Ag Thin Films

SnS∶Ag thin films were deposited on ITO glasses by pulse electro-deposition. By studying the effect of duty cycle on the properties of SnS∶Ag thin films, the optimum off-time(toff) is obtained to be 5 s, namely, the optimal duty cycle is about 67%. The primary phase of SnS∶Ag films deposited on optimum parameters condition is SnS compound with good crystallization, and the films prefer to grow towards (111) plane. The films are dense, smooth and uniform with good microstructure, and the grains in the films are densely packed together, and their direct bandgap is about 1.40 eV. In addition, the bandgap of the films first rises and then drops with the increase of the duty cycle.

Pulse electroforming of nickel under perturbation of hard particles

Nickel deposits were prepared by pulse electroforming, in which an aluminium alloy cylinder mandrel rotated in hard particles filling between the electrodes. The microstructure and properties of the deposits were studied by contrasting with electroforming using direct current. The results show that the surface of the deposits obtained by pulse electroforming displays more obvious abrasion marks and (200) preferred orientation to that electroformed using direct current at the same average current density. Besides, the deposits represent higher microhardness and better high-temperature corrosion resistance. It is also found that the orientation index of plane (200) and microhardness significantly increase with the reduction of duty cycle of pulse current. During pulse electroforming, the longer off-time and higher peak current density are helpful to strengthening the hard particles’ polishing effect on the surface of deposits and perturbing effect on crystal nucleation of atoms.