Zn Ni Alloy Coatings Research Articles

Magnetically induced electrodeposition of Zn–Ni alloy coatings and their corrosion behaviors

The less magnetic features of Zn–Ni alloy compared to Fe–Ni and Fe–Co alloys made it interesting to develop them under the influence of applied magnetic field. In this regard, the effects of a magnetic field (B) applied in a direction parallel and perpendicular to the nominal current, during electrodeposition process of Zn–Ni alloy have been investigated by means of X-ray diffraction and EDX analysis. The modification of crystal orientation by superimposition of a varying magnetic field is studied for alloys of constant nickel content (8a %.), deposited at optimal current density (j) of 3.0Adm−2. The effect of magnetic field on crystallographic orientation and hence the corrosion behaviors of the coatings were studied. The preferential orientations (101) and (002) of the zinc phase and (330) γ-Ni5Zn21 phase are always favored to exist with parallel and perpendicular magnetic field. The preferential (321) γ-Ni5Zn21 orientation is found to be the characteristic of perpendicular magnetic field. Further, Zn (100) orientation is found to be non-responsive to the effect of parallel magnetic field. The coatings developed using perpendicular magnetic field is more corrosion resistant compare to that for parallel magnetic field. This is attributed to the additional (321) γ-Ni5Zn21 orientations. The changes in the phase structure of the coatings deposited at different magnetic field are attributed to the effect caused by the magnetic convection induced in the electrolytic solution, called MHD effect (magneto-hydrodynamic effect). The chemical composition of the alloy was found to be same in both natural and magnetically induced deposition due to constant Ni content in the bath. The variation in the surface morphology of the coatings was studied by scanning electron microscopy (SEM). The Zn–Ni alloy coating deposited at 0.8T perpendicular B showed the highest corrosion resistance (with corrosion rate=0.26×10−2mmy−1) compared to the one with no B (corrosion rate=14.46×10−2mmy−1). The improved corrosion resistance of the coatings was discussed in the light of magnetic field effect on crystallographic orientation.

Influence of Thermal Treatment on the Structure and the Corrosion Resistance of Zn-Ni Alloy Coatings

Electrolytic Zn-Ni alloy coatings were obtained on the steel substrate under galvanostatic conditions, and then, subjected to thermal treatment in argon atmosphere. The influence of thermal treatment on the surface morphology, phase composition and corrosion resistance of the electrodeposited coatings has been studied. Surface morphology was examined using a scanning electron microscopy. Chemical composition was determined by a X-ray fluorescence spectroscopy. Structural studies were carried out using a X-ray diffraction method. Corrosion resistance tests were carried out in 3% NaCl solution using open circuit potential method and potentiodynamic measurements. It was found that after thermal treatment, the value of polarization resistance increases, the value of the corrosion current decreases, and the value of corrosion potential is shifted towards anodic potentials. This suggests a positive effect of thermal treatment of the Zn-Ni alloy coatings on their corrosion resistance.

Characterization of corrosion resistance of electrodeposited Zn–Ni Zn and Cd coatings

The corrosion behavior of electrodeposited Zn–Ni alloy coatings was studied with a view to replace Zn and Cd coatings. A three electrode electrochemical cell was utilized to understand corrosion of the coatings in 3.5% NaCl solution by measuring the open circuit potentials (OCPs), polarization curves and electrochemical impedance spectroscopy (EIS). EIS was performed at intermittent time intervals to understand the extent of dezincification in Zn–Ni alloys and to determine the polarization resistance change with respect to time. Coatings were examined with SEM and XRD to correlate the corrosion behavior with the surface/interface morphology and residual stresses and to understand the nature of corrosion products. The effect of heat treatment and trivalent chrome passivation on the corrosion behavior of Zn–Ni coatings is also reported. Zn–Ni coatings studied here have higher polarization resistance, lower corrosion currents and the corrosion products offer additional protection in increasing the life of the coatings compared with Zn and Cd coatings. Based on these results Zn–Ni coatings are an attractive alternative to Cd and Zn coatings.

The effect of Aeromonas eucrenophila on microbiologically induced corrosion of nickel–zinc alloy

The corrosion behavior of NiZn alloy coatings in nutrient broth medium and in the presence of Aeromonas eucrenophila, isolated from a corroded water treatment system, was studied using electrochemical techniques such as polarization curves, electrochemical impedance spectroscopy (EIS), and mass change of the electrode using a quartz crystal microbalance (QCM). The presence of bacterial attachment on the surfaces, biofilm layer, and corrosion was characterized with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Polarization curves showed that the corrosion current and corrosion current density exhibited a cathodic shift after inoculation that verified an increase in the corrosion rates for NiZn alloy coatings. The QCM experiments showed the mass loss and corrosion effect of A. eucrenophila. Furthermore, FTIR analyses showed the composition and growth of extracellular polymeric substances (EPS) after 5 h, 24 h, and 7 days. The bacterial biofilm that formed on the alloy disc surface increased in coverage and heterogeneity with increased incubation time, resulting in the deterioration of the NiZn alloy coatings below the biofilm in the form of pits and crevices corrosion as shown with SEM images.

Tribocorrosion behavior of Zn, Zn–Ni, Cd and Cd–Ti electrodeposited on low carbon steel substrates

The tribocorrosion behavior of electrodeposited Zn–Ni alloy coatings was investigated with a view to assessing their suitability to replace Zn, Cd and Cd–Ti coatings. A modified pin on flat tribometer in an electrochemical cell was utilized to understand wear induced corrosion of the coatings in 3.5% NaCl solution. Wear tests were conducted at open circuit potentials, and impressed anodic potentials of the coatings to determine the corrosion resistance of coatings before, during and after the wear test. Electrochemical impedance spectroscopy was utilized to understand the polarization resistance of the coatings before and after the wear tests. Wear tracks were analyzed with SEM and XRD to determine the nature of corrosion products and surface morphology changes during the tribocorrosion tests. Zn–Ni coatings had higher polarization resistance after wear test as compared to zinc and cadmium coatings. The mass loss due to wear enhanced corrosion was less with Zn–Ni than with Zn and Cd coatings. Zn–Ni coatings are a suitable replacement to Cd coatings when the surfaces are subjected to simultaneous wear and corrosion.

Preparation Ce(III) conversion coatings on electrodeposited Zn–Ni alloy and comparison of their corrosion performance and morphology with Cr(VI) conversion coatings

Zn–Ni alloy coatings were electroplated on steel after an appropriate pretreatment from tartrate cyanide free alkaline bath. Zn–Ni coatings were obtained with a derivative of imidazol as a brightener agent to form fine grain particles. The Zn–Ni alloy coatings were analysed for phase structure by X-ray diffraction. A cerium based chemical conversion process was developed as an alternative to the chromate process. The cerium conversion coatings improved the corrosion performance. The corrosion behaviour of bare and treated Zn–Ni alloy coatings on steel was evaluated during exposure to 0·5 N NaCl using Tafel polarisation and electrochemical impedance spectroscopy measurements. The morphology and corrosion performance of conversion coatings generated on Zn–Ni alloy coatings in Cr(VI) and Ce(III) treatments were studied and compared. This process may be useful as primer for paints and polymer coatings on steel.

Effect of phosphorus doping on some properties of electroplated Zn–Ni alloy coatings

Zn–Ni alloys were electrodeposited on carbon steel plates and their morphology, composition and structure were evaluated as a function of the amount of Na2H2PO2 added in the plating bath. The presence of phosphorus in Zn–Ni alloys, even in very small amounts, showed effectively a remarkable performance in comparison with the corresponding P-free alloy coating. In fact, Na2H2PO2 added in the plating bath offered a way of optimizing the Ni content in the deposit. Meanwhile, the microhardness was observed to increase. Conversely, these coatings showed smaller crystallite size. Data of XRD had shown that the quantity of η-phase decreased. An inhibitory effect of phosphorus co-deposition was also observed in 3% NaCl solution. Corrosion properties of Zn–Ni alloy coatings were evaluated by means of potentiodynamic polarization and electrochemical impedance spectroscopy. The doped coatings exhibited considerably enhanced corrosion resistance and barrier properties.

Effect of heat treatment on structure and properties of multilayer Zn-Ni alloy coatings

Composition modulated multilayer alloy (CMMA) coatings of Zn-Ni were electrodeposited galvanostatically on mild steel (MS) for enhanced corrosion protection using single bath technique. Successive layers of Zn-Ni alloys, having alternately different composition were obtained in nanometer scale by making the cathode current to cycle between two values, called cyclic cathode current densities (CCCD’s). The coatings configuration, in terms of compositions and thicknesses were optimized, and their corrosion performances were evaluated in 5 % NaCl by electrochemical methods. The corrosion rates (CR)’s of multilayer alloy coatings were found to decrease drastically (35 times) with increase in number of layers (only up to 300 layers), compared to monolayer alloy deposited from the same bath. Surface study was carried with SEM, while XRD was used to determine metal lattice parameters, texture and phase composition of the coatings. The effect of heat treatment on surface morphology, thickness, hardness and corrosion behaviour of multilayer Zn-Ni alloy coatings were studied. The significant structural modification due to heat treatment is not accompanied by any decrease in corrosion rate. This effect is related to the formation of a less disordered lattice for multilayer Zn-Ni alloy coatings.

Structural and corrosion characterisation of pulse plated Zn and Zn–Ni alloy coatings

The effects of pulse plating on the phase and chemical composition, preferred orientation and surface morphology of Zn and Zn–Ni (12 wt-%) electrodeposited coatings have been investigated using atomic force microscopy, scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy and electrochemical techniques. It has been established that pulse current plating with respect to direct current (dc) conditions resulted in ∼50% reduction in the grain size dimensions and in fourfold and twofold reduction in the corrosion current densities of Zn and Zn–Ni coatings respectively. Under all the pulse plating conditions applied the deposited alloy consisted of the single γ-Zn21Ni5 phase, while, according to the XRD measurements both coatings possessed inclusions of the oxide phase. The analysis of the protective properties and the thickness of the oxide films formed on the surface of investigated coatings revealed the fact that the surfaces of pulse plated samples were favourable for the formation of thinner oxide films which at the same time exhibited higher protective properties. Pulse plating increased the amount of non-metallic inclusions in Zn and Zn–Ni coatings, however, these amounts were not high, as the O concentration in the deposits did not exceed 1·5 and 0·2 wt-% for Zn and Zn–Ni respectively.

Microbiologically influenced corrosion of NiZn alloy coatings by Delftia acidovorans bacterium

In this study, Delftia acidovorans was isolated from water treatment pipe system and used to demonstrate microbiologically influenced corrosion of NiZn alloy coatings using electrochemical techniques. The surface morphologies and the corrosion products were determined using scanning electron microscopy (SEM) and energy dispersive X-ray spectra (EDS) analysis. Results showed that when the metabolic activity reached maximum level, corrosion activity of NiZn alloy coatings significantly increased in correlation with Ecorr, Icorr, QCM and Rct. Furthermore, crevice corrosion which has been seen due to bacterial adhesion confirms that D. acidovorans plays an important role in corrosion of NiZn alloy coating.

Tribological behavior of electrodeposited Zn, Zn–Ni, Cd and Cd–Ti coatings on low carbon steel substrates

The tribological behavior of electrodeposited Zn–Ni alloy coatings was investigated for its suitability to replace Zn- and Cd-based coatings. An in situ tribometry technique with a transparent sapphire hemisphere as a counter face on a pin on flat tribometer was utilized to examine the contribution of third bodies in friction and wear behavior. Wear mechanisms and tribo/transfer film morphology were also studied with the X-ray diffraction and electron microscopy. In situ tribometry and additional ex situ analyses revealed that Zn–Ni coatings had superior resistance to adhesive wear compared to cadmium coatings. Microhardness of Zn–Ni coatings was higher than Zn and Cd coatings. Hardness on the wear track of Zn–Ni coatings showed the formation of a strain hardened tribo layer.

Effect of diethanolamine and triethanolamine on the properties of electroplated Zn–Ni alloy coatings from acid bath

AbstractIn the present work, zinc–nickel alloy coatings have been produced under direct current conditions from an acid bath with different concentrations of diethanolamine (DEA) and triethanolamine (TEA). The produced coatings were analysed through chronopotentiometry, microhardness, X‐ray diffraction and MEB techniques. The compositional analysis of the films showed that the Zn–Ni electrodeposition is anomalous for all the systems. Ethanolamines augmented the anomalous behaviour. The hindering in the Ni (II) reduction will be more effective due to complexation of Ni (II) catalyst with ethanolamines. Electrochemical and structure analysis of deposits indicated the presence of γ and highly Zn‐enriched phases. The presence of these additives resulted also in coatings with finer grains. The behaviour of modified Zn–Ni alloy coatings in corrosion solution of 3% NaCl was investigated through potentiodynamic polarisation and electrochemical impedance spectroscopy. It was found that the obtained Zn–Ni/3 mM TEA alloy exhibited better corrosion resistance compared to pure Zn–Ni alloy electrodeposited at similar conditions. © 2012 Canadian Society for Chemical Engineering

Study of corrosion performance of electrodeposited nanocrystalline Zn–Ni alloy coatings

The corrosion performance of nanocrystalline Zn–Ni alloy coatings electrodeposited from an alkaline bath using direct current has been investigated using EIS and polarization curves technique. Performance of these nanocrystalline alloy coatings with various Ni content was compared to that of microcrystalline Zn–Ni alloy. The corrosion product formed on the nanocrystalline Zn–Ni alloy coatings is stable and protective which proves to be better compared with microcrystalline. The nanocrystalline Zn–Ni alloy with 17.62wt.% Ni and grain size 37nm gives the best performance of the Zn–Ni alloy coatings tested. The corrosion resistance of nanocrystalline alloy coatings depends on the chemical compositions.

Formation of compositionally modulated Zn–Ni alloy coatings on steel

The results of experiments involving the compositionally modulated multilayer Zn–Ni alloy coatings obtained by electrochemical method are presented. The determination of morphology, corrosion resistance and surface roughness of obtained coatings and their hardness by Vickers method were described. It was found that coatings consisting of the highest number of sublayers (50) were characterised as having the best anti-corrosion properties, which arise from the alternating (anodic/cathodic) mechanism of the corrosion process and from the influence of the formed corrosion products. The multilayer structure of the obtained coatings also influenced coating morphology and the hardness of the obtained system.

Study of Zn-Ni Alloy Coatings Modified by Nano-SiO2Particles Incorporation

The aim of this research work was to codeposit nano-SiO2particles into Zn-Ni alloy coatings in order to improve some surface properties. It had been investigated the effect of loading the plating bath with nanoparticles on composition, morphology, phase structure of deposits, and their subsequent influence on the corrosion process in corrosive solution of 3% NaCl and the thermal stability of deposits at200°C. It was found that Zn-Ni alloy composites contain a higher percentage of Ni with incorporation in the deposit of 1.54% of silica. X-ray diffraction measurements revealed that the alloys consisted of two phases, pure zinc andγphase. Electrochemical characterization of the composites had been carried out through potentiodynamic polarization and electrochemical impedance spectroscopy. The composites exhibited higher values of microhardness and better corrosion resistance in corrosive media.

Corrosion behaviour of zinc–nickel alloy coatings electrodeposited in additive free chloride baths

Corrosion behaviour of nanocrystalline Zn–Ni alloy coatings (with 3 to 18 at-%Ni) electrodeposited on steel substrate from additive free chloride baths by DC plating has been investigated by measurement of open circuit potential with time and neutral salt spray test. The alloy coatings containing up to 16 at-%Ni exhibited an increase in resistance to the appearance of white and red rust with increasing Ni content. The resistance to the appearance of white rust and ability to protect the underlying steel substrate decreased with further increasing Ni content. This has been considered to be due to reduced passivating ability of the alloy coating with a significant rise in the grain size above 50 nm.

Corrosion stability of electrodeposited cyclic multilayer Zn–Ni alloy coatings

This paper reports on a study of electrodeposition and characterisation of cyclic multilayer coatings of Zn–Ni alloy from a sulphate bath. Cyclic multilayer alloy coatings were deposited on mild steel through the single bath technique by appropriate manipulation of cathode current densities. The thickness and composition of the individual layers of the CMA deposits were altered precisely and conveniently by cyclic modulation of the cathode current during electrodeposition. Multilayer deposits with sharp change in composition were developed using square current pulses, using thiamine hydrochloride and citric acid as additives. Laminar deposits with different configurations were produced and their corrosion behaviours were studied by AC and DC methods in 5%NaCl solution. It was observed that the corrosion resistance of the CMA coating increased progressively with the number of layers (up to certain optimal numbers) and then decreased. The decrease in corrosion resistance at high degree of layering was attributed to interlayer diffusion due to less relaxation time for redistribution of metal ions at cathode during deposition. The coating configurations have been optimised for peak performance of the coatings against corrosion. It was found that CMA coating developed at cyclic cathode current densities of 3·0/5·0 A dm−2 with 300 layers showed the lowest corrosion rate (0·112×10−2 mm/year) which is ∼54 times better than that of monolithic Zn–Ni alloy, deposited from the same bath. The protection efficacy of CMA coatings is attributed to the difference in phase structure of the alloys in successive layers, deposited at different current densities, evidenced by X-ray diffraction analysis. The formation of multilayers and corrosion mechanism were examined by scanning electron microscopy.

Electrodeposition of nanocrystalline Zn–Ni alloy from alkaline glycinate bath containing saccharin as additive

Nanocrystalline Zn–Ni (crystallite sizes 13–68 nm) alloy coatings were produced from an alkaline glycinate bath containing saccharin as additive. X-ray diffraction (XRD) was used to determine the phase composition and average crystallite size of nanocrystalline Zn–Ni alloy coatings. The average grain size of a deposit was also studied by transmission electron microscopy (TEM). The effects of saccharin concentration and current density on the crystallite size and surface roughness of the coatings were studied. Crystallite size and average surface roughness were diminished as a result of increasing saccharin concentration. Scanning electron microscopy (SEM) examination showed that coatings had a colony-like morphology and the colony size was increased with increasing current density. Microhardness testing was carried out in order to determine the degree of dependence of this mechanical property on the crystallite size. It was found that microhardness did not depend on crystallite size (Hall–Petch).

Corrosion Protection of Steel Parts in Aircraft by Zn-Mn Alloy Electrodeposits

Electrodeposited Zn-Fe, Zn-Co and Zn-Ni alloy coatings are widely used for corrosion protection of steel nowadays. Several authors have reported that in aggressive environments, such as atmosphere containing SO2 and chloride compounds, Zn-Mn alloy coatings can have even better corrosion resistance. Besides, these alloys possess high hardness and they can easily be painted. Good characteristics of Zn-Mn alloys suggest their possible application in protection of steel parts, especially in automobile and aircrafts. In the last ten years, three new types of electrolytic solutions for electrodeposition of Zn-Mn alloys were proposed, namely acidic chloride and sulphate and alkaline pyrophosphate solution. The scope of this work was to compare the corrosion protection ability of Zn-Mn alloy coatings electrodeposited under various parameters, such as type of electrolytic solution, concentration of metal ions in solution and deposition current density. Recording of corrosion potential and salt spray chamber measurements were used to investigate the corrosion stability of Zn-Mn coatings. It was concluded that Zn-Mn alloy had better corrosion resistance than pure Zn, due to the formation of compact protective-passive layer in chloride containing media. Among various Zn-Mn electrodeposits, the best corrosion behavior was obtained for the ones deposited from chloride solution, at current densities between 3 and 8 A dm-2.

Development of nano-structured cyclic multilayer Zn-Ni alloy coatings using triangular current pulses

Cyclic multilayer alloy (CMA) deposits of Zn-Ni were developed on mild steel from sulphate bath having thiamine hydrochloride (THC) and citric acid (CA) as additives. CMA coatings were developed galvanostatically using triangular current pulses, under different conditions of cyclic cathode current density (CCCD’s) and number of layers. The corrosion behaviors of the coatings were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy methods, and were compared with that of monolayer Zn-Ni alloy of same thickness. At optimal configuration, CMA coating represented as, (Zn-Ni)2.0/5.0/300 was found to exhibit ∼40 times better corrosion resistance compared to monolayer alloy, (Zn-Ni)3.0. Cyclic voltammetry study demonstrated that THC and CA have improved the appearance of the deposit by complexation with metal ions. The corrosion protection efficacy of CMA coatings was attributed to the difference in phase structure of the alloy in successive layers, evidenced by XRD analysis. The formation of multilayer and corrosion mechanism was analyzed by Scanning Electron Microscopy (SEM) study.