Influence of Zn-Ni alloy electrodeposition techniques on the coating corrosion behaviour in chloride solution

The aim of this research work is to optimize the plating conditions during electrodeposition of Zn-Ni alloys. Electrodeposits of Zn-Ni alloys have been synthesized from sulphate bath using cyclic voltammetry and chronopotentiometry techniques under different conditions. X-ray diffraction measurements reveal that the alloys consisted of <gamma>-Ni₅Zn₂₁ and pure zinc phases. The composition and morphology of the deposits have been also studied and discussed. The surface analyses indicate that the deposition took place with the formation of Zn-Ni alloy coatings, containing at least 10 wt.% Ni. In order to obtain better barrier properties and corrosion resistance, coated steel samples have been immersed in 3% NaCl solution and studied using potentiodynamic stripping and electrochemical impedance spectroscopy. The process of dezincification is reduced when the coated steel is electroplated by chronopotentiometry (5 mA and 10 mA). In addition, these samples exhibit an improved morphology and fine grain size as compared with deposits electroplated by cyclic voltammetry.     

Corrosion study of Ni/Zn compositionally modulated multilayer coatings using electrochemical impedance spectroscopy

Ni/Zn compositionally modulated multilayer (CMM) coatings were deposited using dual bath technique. Coatings corrosion performance was evaluated using electrochemical impedance spectroscopy (EIS) during extended immersion times up to 48 h. The results of electrochemical impedance spectroscopy showed that Ni/Zn CMM coatings had better corrosion resistance compared to that of the zinc single layer coating. The modified corrosion product which is formed on the Ni/Zn CMM coatings during extended exposure times and also a good barrier effect of the nickel layer against aggressive species in these coatings can be two important reasons for high corrosion performance and so protection performance of the Ni/Zn CMM coatings.     

Electrochemical studies on the electrodeposited Zn-Ni-Co ternary alloy in different media

The electroplating of ternary Zn-Ni-Co alloy, surface morphology and corrosion resistance were investigated and contrasted with the characteristics of Zn-Ni electrodeposits. The investigation of electrodeposition was carried out using cyclic voltammetry and galvanostatic techniques, while potentiodynamic polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Under the examined conditions, the electrodeposition of the alloy was of anomalous type. It was found that the obtained Zn-Ni-Co alloy exhibited more preferred surface appearance and better corrosion resistance compared to Zn-Ni alloy that electrodeposited at similar conditions. During the cathodic scan of cyclic voltammetry, a cathodic peak at − 574 mV is appeared and correlated with the deposition of sulfur liberated from the reduction of sulphate group in the presence of H⁺. Up to four anodic peaks were obtained by cyclic voltammetry technique, two correlated with zinc oxidation from pure deposited Zn and γ-Ni₅Zn₂₁ phases and two correlated with oxidation of cobalt and nickel, were observed. The phase structure, surface morphology and chemical composition of the deposits were characterized by means of X-ray diffraction analysis, scanning electron microscopy and atomic absorption spectroscopy, respectively.     

Electrodeposition of Zn-Ni, Zn-Fe and Zn-Ni-Fe alloys

Zn-Fe, Zn-Ni and Zn-Ni-Fe coatings were electrodeposited galvanostatically on mild steel from acidic baths (pH 3.5) consisted of ZnCl₂, NiCl₂, FeCl₂, gelatin, sulfanilic (p-aminobenzenesulfonic) acid and ascorbic acid. Cyclic voltammetry showed that the effect of gelatin was more pronounced than that of sulfanilic acid, and that the deposition of the ternary alloy behaved differently from the deposition of the binary alloys. In all three systems, the Faradaic efficiency was higher than 88%, the rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, and the deposition was of anomalous type. For each applied current density, the concentrations of Ni and Fe in the ternary alloy were higher than the corresponding concentrations in the binary alloys. The hardness of Zn-Ni coatings was the highest, while that of Zn-Fe coatings was the lowest. The Zn-Ni-Fe coatings were the smoothest, had distinguished surface morphology, and contained ZnO in the bulk, not just on the surface. The lowest corrosion rate in each alloy system (214, 325 and 26 μm year⁻¹ for Zn-Ni, Zn-Fe and Zn-Ni-Fe, respectively) was characteristic of coatings deposited at 30, 30 and 40 mA cm^− 2, respectively. The higher corrosion resistance of the ternary alloy was also reflected by a higher corrosion potential, a higher impedance and a higher slope of the Mott-Schottky line. The enhanced corrosion behavior of the ternary alloy was thus attributed to its chemical composition, phase content, roughness and the synergistic effect of Ni and Fe on the n-type semiconductor surface film.     

Effect of electrodeposition conditions on the composition, microstructure, and corrosion resistance of Zn-Ni alloy coatings

The formation, composition, and structure of electrodeposited zinc-nickel alloys were investigated. It has been shown that both anomalous and normal codeposition of zinc and nickel can be realized by changing the bath composition and deposition conditions, with the nickel content in the resultant deposit being varied in a wide range (from 2 to 90 at.%). It has been also shown that the ammonical diphosphate electrolyte allows deposition of Zn-Ni coatings with a homogeneous phase structure (Ni₅Zn₂₁ and Ni₃Zn₂₂ intermetallides, a solid solution of Zn in Ni, or a solid solution of Ni in Ni₅Zn₂₁), whereas the weak acid chloride electrolyte produces two-phase coatings consisting of Ni₅Zn₂₁ with the admixture of polycrystalline Zn or Ni. The Zn-Ni coating with a nickel content of 19 at.% consisting of Ni₅Zn₂₁ intermetallic phase exhibits the highest corrosion resistance.     

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.     

Corrosion resistance of Zn–Ni/Ni and Ni/Zn–Ni compositionally modulated multilayer coating

Zn–Ni/Ni and Ni/Zn–Ni compositionally modulated multilayer (CMM) coatings were prepared by dual‐bath technique. The effects of layers number and sublayers order were studied. Specially, the effect of different sublayers thickness ratios with the same multilayer period (λ) on the corrosion resistance of the CMM coatings was investigated in detail. Results showed that the corrosion resistance of Ni/Zn–Ni (Zn–Ni alloy sublayer as the top layer) CMM coating was better than that of Zn–Ni/Ni (Ni sublayer as the top layer) CMM coating. The 6‐layer CMM coating with the layer thickness ratio of Ni/Zn–Ni = 0.8:1.2 (λ = 2 µm) has the best corrosion resistance.     

Fabrication of Zn?Ni/Ni?P compositionally modulated multilayer coatings

Zn? Ni/Ni? P compositionally modulated multilayer (CMM) coatings which have a novel three‐dimension (3d) latticed multilayer structure were prepared by dual‐bath technique. The formation of the special 3d latticed structure was investigated. The adhesion and corrosion resistance of the CMM coatings were studied. The results showed that the special 3d latticed multilayer structure, which was different from the structure of traditional CMM coatings, was formed during Ni? P electroless plating. The 3d latticed structure benefited the adhesion and corrosion resistance of the novel CMM coatings. The barrier effect of the 3d latticed structure is enhanced.     

Corrosion stability of electrodeposited cyclic multilayer Zn–Ni alloy coatings

Abstract

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.     

Comparison of corrosion-resistance and hydrogen permeation properties of Zn-Ni, Zn-Ni-Cd and Cd coatings on low-carbon steel

Zn-Ni-Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion and hydrogen permeation characteristics of Zn-Ni-Cd alloy coatings electrodeposited from alkaline bath were studied and compared with those of Cd and Zn-Ni coatings obtained using commercial baths. Zn-Ni-Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion potential of this Zn-Ni-Cd coating was −0.62 V vs. SCE, which is still negative potential compared to iron. The corrosion rate of Zn-Ni-Cd coated steel was 0.073 mm y⁻¹, which is estimated in a solution at a pH of 7. This value is much lower than the corrosion rate of Zn-Ni alloy (0.502 mm y⁻¹) and Cd (0.306 mm y⁻¹) coatings deposited from commercial baths. Zn-Ni-Cd alloys are also demonstrated to have superior hydrogen permeation inhibition properties compared to Cd and Zn-Ni coatings. Kinetic parameters of hydrogen permeation such as the transfer coefficient, α, the modified exchange current density, i₀^′, thickness dependent adsorption-absorption rate constant, k^″, recombination rate constant, k₃, surface hydrogen coverage, θ_s, were evaluated by applying a mathematical model to analyze experimental results.     

Tribological behaviour and residual stress of electrodeposited Ni/Cu multilayer films on stainless steel substrate

In the present study, [Ni (4.5 nm)/Cu (t_Cu = 2, 4 and 8 nm)] multilayers were pulse electrodeposited on stainless steel (AISI SS 304) substrate from sulphate based single bath technique. X-ray diffraction (XRD) was used to investigate the structure and stress of the Ni/Cu multilayer. The results from XRD analysis indicated that the deposited multilayers had a preferred crystal orientation of [111] and presence of satellite reflection suggested the formation of superlattice. The stress level within the deposited multilayers was found to be sensitive to the sublayer thickness. Sliding wear behaviour of electrodeposited Ni/Cu multilayer films has been investigated against a tungsten carbide (WC) ball as the counter body and compared with that of the constituents, Cu and Ni coatings. The wear tests were carried out by using a reciprocating ball-on-flat geometry at translation frequencies of 5 and 10 Hz, slip amplitude of 1 mm and at five different loads of 3, 5, 7, 9 and 11 N. Friction force was recorded on-line during the tests. At the end of the tests, the wear scars were examined by laser surface profilometry and scanning electron microscopy (SEM). Friction coefficient was found to be dependent on load and Cu layer thickness (t_Cu) and the values for multilayers were border between Ni and Cu. Among multilayers, sample with minimum t_Cu has shown the lowest friction coefficient and wear rate. With increasing t_Cu, the wear mechanism changes from pure abrasive wear at t_Cu = 2 nm, to particle entrapment at t_Cu = 4 nm to particle embedding at t_Cu = 8 nm. Detailed investigation of the wear scar morphology as well as wear rate measurement revealed that at low loads, (H/E) ratio and residual stress governed the wear rate and the principle wear mode was abrasive cutting. At intermediate loads, the role of residual stress became insignificant while wear was governed by (H/E) ratio and plastic deformation. However, at higher loads, plastic deformation played the major role.     

Ni-TiO2 nanocomposite coating with high resistance to corrosion and wear

Ni-TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were prepared by electrodeposition in a Ni plating bath containing TiO₂ nanoparticles to be codeposited. The influences of the TiO₂ nanoparticle concentration in the plating bath, the current density and the stirring rate on the composition of nanocomposite coatings were investigated. The composition of coatings was studied by using energy dispersive X-ray system (EDX). The wear behavior of the pure Ni and Ni-TiO₂ nanocomposite coatings were evaluated by a pin-on-disc tribometer. The corrosion performance of coatings in 0.5 M NaCl, 1 M NaOH and 1 M HNO₃ as corrosive solutions was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy methods (EIS). The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO₂ nanoparticle content in the coating. With increasing of TiO₂ nanoparticle content in the coating, the polarization resistance increases, the corrosion current decreases and the corrosion potential shifts to more positive values.     

TiN/Cr/Al2O3 and TiN/Al2O3 hybrid coatings structure features and properties resulting from combined treatment

New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al₂O₃ coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H₂SO₄, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al₂O₃ sub-layers mixing).     

Influence of deposition conditions on mechanical and tribological properties of nanostructured TiN/CNx multilayer films

Nanostructured TiN/CN_x multilayer films were deposited onto Si (100) wafers and M42 high-speed-steel substrates using closed-filed unbalanced magnetron sputtering in which the deposition process was controlled by a closed loop optical emission monitor (OEM) to regulate the flow of N₂ gas. Multilayers with different carbon nitride (CN_x) layer thickness could be attained by varying the C target current (0.5 A to 2.0 A) during the deposition. It was found that the different bilayer thickness periods (i.e. the TiN layer thickness Λ_TiN was fixed at 3.0 nm while the CN_x layer thickness Λ_CNx was varied from 0.3 to 1.2 nm) significantly affected the mechanical and tribological properties of TiN/CN_x multilayer films. These multilayer films were characterized and analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), Rockwell-C adhesion test, scratch test, pin-on-disc tribometer, and nanoindentation measurements. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN_xO_y and TiO_2, existed in a TiN layer. Nanoindentation results showed that the hardness was highly dependent on the bilayer thickness. A maximum hardness of ~ 41.0 GPa was observed in a multilayer film at bilayer thickness Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm. All multilayer films exhibited extreme elasticity with elastic recoveries as high as 80% at 5 mN maximum load. The compressive stresses in the films (in a range of 1.5-3.0 GPa) were strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. By scratch and Rockwell-C adhesion tests, the multilayer films with smaller bilayer thicknesses (Λ_TiN = 3.0 nm, Λ_CNx = 0.3 and 0.6 nm) exhibited the best adhesion and cohesive strength. The critical load value obtained was as high as ~ 78 N for the films with Λ_TiN = 3.0 nm, Λ_CNx = 0.9 nm. The friction coefficient value for a multilayer at Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm was found to be low 0.11. These adhesive properties and wear performance are also discussed on the basis of microstructure, mechanical properties and tribochemical wear mechanisms.     

The effects of niobium and nickel on the corrosion resistance of the zinc phosphate layers

In this investigation the viability of nickel substitution by niobium in zinc phosphate (PZn) baths has been studied. Samples of carbon steel (SAE 1010) were phosphated in two baths, one containing nickel (PZn + Ni) and the other with niobium substituting nickel (PZn + Nb). Potentiodynamic polarization curves (anodic and cathodic, separately) and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion resistance of the phosphated carbon steels in a 0.5 mol L^− 1 NaCl electrolyte. The phosphate layers obtained were analysed by X-ray diffraction and it was found that they are composed of Zn₃(PO₄)₂.4H₂O (hopeite) and Zn₂Fe(PO₄)₂.4H₂O (phosphophylite). Surface observation by scanning electron microscopy (SEM) showed that the PZn + Ni layer is deposited as needle-like crystals, whereas the PZn + Nb layer shows a granular morphology. The electrochemical results showed that the PZn + Nb coating was more effective in the corrosion protection of the carbon steel substrate than the PZn + Ni layer. The results also suggested that nickel can be replaced by niobium in zinc phosphate baths with advantageous corrosion properties of the layer formed.     

Characterization of electroless Ni-based alloys for use in bipolar plates of direct methanol fuel cells

In this study, an electroless Ni-P deposit is employed as an anodic coating layer to protect the metallic bipolar plate of a direct methanol fuel cell (DMFC). An inductively coupled plasma-mass spectrometer, grazing incidence X-ray diffractometer, and potentiodynamic polarization measurements were used to study changes in the composition, crystalline structures and corrosion resistance of the Ni-P deposits at various bath pHs and temperatures. The crystalline structure of the Ni-P deposits was observed to change from crystal to amorphous as the P content increased, thus enhancing the corrosion resistance of the plate. The optimal conditions for obtaining the highest P content were found to be at pH 4.3 and 70 °C. Furthermore, the potentiostatic test for the Ni-P deposits prepared under the optimal condition was performed in a simulated anode working environment (0.5 M H₂SO₄ + 10 vol.% methanol), with the test showing that a negative corrosion current was observed at all times, therefore indicating that cathodic protection was employed throughout. Even after 10 h of potentiostatic treatment, no metal ions were found in a test solution. In addition, the result of a DMFC performance test demonstrated that bipolar plates using an anticorrosion coating of Ni-P deposits obtained a lower bulk resistance and an enhanced cell performance when compared to commercially available plates. Hence, the low-cost electroless Ni-P deposit demonstrates high potential for use as a corrosion protection layer in a DMFC bipolar plate with a Cu interlayer.     

The corrosion behaviour of Fe-15Mn-7Si-9Cr-5Ni shape memory alloy

The corrosion behaviour of Fe-15Mn-7Si-9Cr-5Ni (mass%) shape memory alloy at 25 °C in 0.5 M H₂SO₄ and 3.5% NaCl solutions has been studied using potentiodynamic polarization and electrochemical impedance techniques. Three different microstructures viz., single-phase γ, γ-δ and γ-Fe₅Ni₃Si₂, were produced by heat-treating the alloy in different equilibrium phase fields. The corrosion behaviour in 0.5 M H₂SO₄ solution is almost same for all three microstructures, barring a slight difference in the passivation range. Although, the passivation current in 0.5 M H₂SO₄, is in the same range as that of SS 304, the critical current required for onset of passivation is almost three orders higher and the passivation range is much shorter. In 3.5% NaCl solution the corrosion behaviour of all three microstructures of the Fe-15Mn-7Si-9Cr-5Ni shape memory alloy was that of general dissolution without passivity or localized attack (pitting). The best corrosion resistance in both H₂SO₄ and NaCl solutions is shown by the single-phase γ microstructure.     

Study of surface roughness and corrosion performance of Ni/Zn–Fe and Zn–Fe/Ni compositionally modulated multilayer coatings

Compositionally modulated multilayer coatings consisting alternative layers of nickel and zinc–iron alloy were electroplated using dual bath technique. The coating's surface morphology was studied using a scanning electron microscope. The effects of coatings configuration, i.e., order and the number of layers on the coatings surface roughness was investigated. It was observed that as the number of layers increases in the different Ni/Zn–Fe CMM coatings, 2 and 4-layer Zn–Fe/Ni CMM coatings the final surface roughness is decreased due to the lower grain growth of zinc–iron individual layers. The coatings corrosion protection performance was evaluated using Tafel extrapolation, anodic polarization and salt spray tests. The results of corrosion study showed that all Ni/Zn–Fe and Zn–Fe/Ni CMM coatings, except the 8-layer Zn–Fe/Ni coating, had a better corrosion protection performance compared to the single layer zinc–iron alloy coating or nickel coating.     

Nanofabricated multilayer coatings of Zn-Ni alloy for better corrosion protection

As an effort to increase the corrosion resistance of conventional monolayer Zn-Ni alloy coating, the multilayer Zn-Ni alloy coating have been done electrolytically on mild steel (MS), using gelatin and glycerol as additives. Multilayered, or more correctly composition modulated multilayer alloy (CMMA) coatings have been developed using square current pulse. Successive layers of alloys, in nanometric scale having alternately changing composition were fabricated by making the cathode current to cycle between two values, called cyclic cathode current densities (CCCD’s). The coatings having different configuration, in terms of composition and thicknesses of individual layers were developed and their corrosion performances were evaluated by electrochemical methods. The corrosion rate (CR)’s were found to decrease drastically with progressive increase in number of layers (up to 300 layers), and then increased. The coating configurations have been optimized for best protection against corrosion. The CMMA Zn-Ni coating having 300 layers was found to be about 37 times more corrosion resistant than corresponding monolayer alloy, developed from same bath for same time. High protection efficacy of the coatings were attributed to alternate layers of alloys having different surface structure and composition, supported by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) study, respectively. Optimization procedure has been explained, and results are discussed.     

Evaluation of the corrosion protection properties of multilayer Cu/Ni/Cr deposits

Investigations of multilayer Ni/Cr deposits with conventional and with microporous chromium, in some cases incorporating bright copper sublayers, are reported.The microporosity of the chromium deposit is determined by the Dubpernell test. The polarity, the potential differences and the thicknesses of the individual nickel deposits are determined using the simultaneous thickness and electrochemical potential (STEP) test. Accelerated corrosion determinations are carried out using the Corrodkote method.The superposition of the duplex nickel (semibright nickel (SBNi) or bright nickel (BNi) and nickel seal (Ni_s)), microporous chromium and bright copper (BCu) sublayer on nickel strike (Ni_str) in the system Ni_str(2 μm)/ BCu(20 μm)/SBNi(9 – 12 μm)/Ni_s(3 – 5 μm)/Cr(0.3 μm) leads to the formation of multilayer protective and/or decorative plates with the best corrosion protection properties.It is possible to use the fast STEP test in combination with the Dubpernell method to forecast the corrosion behaviour of multilayer Cu/Ni/Cr deposits.