Zn Ni Coatings Research Articles

Controlled Compositions in Zn–Ni Coatings by Anode Material Selection for Replacing Cadmium

Cadmium-based coatings have long been used to protect high-strength steel in aerospace, but due to cadmium’s toxic and carcinogenic nature, its use is increasingly restricted. Zinc–nickel coatings, containing 10–14 wt% Ni, offer superior corrosion resistance compared to pure zinc, making them a promising alternative. However, Zn–Ni coatings are prone to cracking, which can compromise their protection. This study investigates how different anode materials influence crack formation and coating properties during electrodeposition. Zinc and nickel anodes produced coatings with consistent thicknesses of 13–15 µm, while 1020 steel and stainless steel resulted in thicker coatings of up to 33 µm. Notably, coatings deposited with nickel anodes demonstrated strong adhesion and consistent interface quality. Zinc anodes achieved a high Ni content of about 13.5 wt%, whereas 1020 steel and stainless steel produced lower Ni content, around 7 wt%. Additionally, zinc and nickel anodes led to fewer defects and minimal porosity, in contrast to the higher porosity observed with 1020 steel and stainless steel anodes. Furthermore, zinc anodes maintained stable voltages (~0.5 V), contributing to more uniform coatings. In terms of corrosion resistance, zinc anodes exhibited a lower corrosion rate of 0.44 mm/year compared to 1.54 mm/year for nickel anodes. This study highlights the importance of anode selection in reducing cracking and optimizing Zn–Ni coatings, presenting them as a safer and more effective alternative to cadmium-based coatings.

Physicochemical, Morphological and Anticorrosive Properties of Electrodeposited ZnNi Alloy Coating

Corrosion in its many forms is a major problem for many types of materials, extending from machining to manufacturing and daily use. In fact, it affects practically all engineering projects, from the biggest to the smallest: energy production, construction, transport, medical sector, electronics, etc. Consequently, corrosion generates both economic and environmental problems. To prevent corrosion and preserve materials' durability, several protection methods can be applied. These included protection by applying a coating on the metal surface. In this context, Zinc based alloy coatings have attracted much interesting scientific community because of their excellent mechanical and anti-corrosive properties. In the present work, ZnNi coatings were electrodeposited on steel substrates using a chloride bath containing ammonium salts. The effect of some experimental parameters, namely, potential and metal ion concentration ratio on the deposition kinetics of ZnNi system as well as on its physicochemical, morphological and anticorrosive properties has been investigated. For this purpose, an appropriate experimental work was performed by using both electrochemical (cyclic voltammetry, chronoamperometry, open circuit potential, potentiodynamic polarization) and nonelectrochemical (SEM-EDX) analysis methods. Based on the obtained results, it has been revealed that simultaneous codeposition of both elements Zn and Ni is possible in our experimental conditions. However, deposition kinetics exhibited a strong dependence on explored parameters. Also, morphological aspect and chemical composition of deposits are strongly influenced by metal ion concentration ratio. Investigation of corrosion behaviour confirms the protective effect of coatings acted as a sacrificial anode. Furthermore, increasing Ni content in the deposits induces a significant enhancement in corrosion resistance. Thus, Zn-Ni alloy coatings prepared from the Ni(II)-rich bath exhibited better corrosion resistance.

Effect of complexing agent on iron base zinc-nickel alloy coating

The influence of four complexing agents on corrosion resistance of Zinc-Nickel (Zn-Ni) alloy coating was investigated. The current density and plating time were determined by Hull and rectangular tank experiments. The effects of triethanolamine, potassium sodium tartrate, tetraethylenepentamine and sodium citrate on the properties of iron-based Zn-Ni alloy coatings were studied under the same electroplating process. The surface morphology, structure, elemental composition and corrosion resistance of Fe-base Zn-Ni alloy coatings with different complexing agents were analyzed. The surface and morphology of the coating were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The anticorrosive properties of the coating were evaluated by electrochemical electrode and electrochemical impedance spectroscopy (EIS). The self-corrosion current density of triethanolamine is 2.927e-005A·cm−2, the rate of corrosion is minimal, rendering the material highly resistant to corrosion; the surface remains flat and exhibits a dense texture. The content of potassium, sodium, Zn and Ni in tartrate increased, thus reducing the corrosion resistance and flatness of the coating. The self-corrosion current density was 9.400e-005A·cm−2. The surface was rough and uneven, and there were a large number of large concave and convex defects. The complexing agent enhances the adhesion and corrosion resistance of the coating, improves the optical and mechanical properties of the coating, adjusts the durability and stability of the coating, increases the crystal packing density, increases the coating thickness, improves the adhesion with the substrate interface, and optimizes the uniformity of grain distribution. These factors are the key factors that determine the corrosion behavior of Zn-Ni coatings. In the process of electroplating, the addition of complexing agent can improve the quality of the coating, and suitable complexing agent can obtain smooth and bright coating at the same time, make the corrosion resistance of the coating higher.

Effect of ultrasound assistance on the mechanical performance and corrosion resistance of Zn-Ni coatings produced by cathode plasma electrolysis deposition

Zn-Ni coatings were fabricated via ultrasonic-assisted cathodic plasma electrolysis deposition (US-CPED) technology. The results demonstrate that ultrasonic assistance can significantly affect the deposition and growth process of Zn-Ni coatings, which is attributed to ultrasonic vibration reducing the diameter of bubbles and inducing a more uniform distribution of the vapor gaseous envelope (VGE) on the surface of the substrate. The Zn-Ni coatings with more homogeneous microstructure were formed due to the more uniform plasma discharge process on the surface of the substrate based on the VGE uniform distribution. Compared to the Zn-Ni coatings without ultrasonic assistance, the thickness and roughness of Zn-Ni coatings with ultrasonic assistance increased by >80 % and decreased by over 40 %, respectively. Better Zn-Ni coating quality brings higher corrosion resistance. In addition, ultrasound can accelerate the iteration of bubbles in VGE to enhance the work-hardening effect, improving the mechanical properties of the Zn-Ni coatings. This work introduces a novel insight into the controllability of the CPED process and paves the way for exploring other methods to stabilize the CPED process.

Effect of Different Passivation Treatments on Alkali Zn-Ni Coatings: Corrosion Resistance and Adhesion Performance of Geomet 321 and ML Black Coatings

This study aims to improve the corrosion properties of (AISI 1040) materials used in the automotive industry. For this purpose, two different coating techniques were applied to the same surface. As part of the research, different passivation processes (transparent, blue, yellow, and black) were applied to alkaline Zn-Ni coatings. Geomet 321 and Geomet ML Black coatings were deposited on the passivation layer to form a double-layer coating. In order to investigate the adhesion and corrosion effects of these coatings, a dry adhesion test, a water test, a humidity test, and a salt spray test were carried out, and cross-cut adhesion tests were carried out after each corrosion test. After all these tests, rust formation was analysed by visual analysis, and atomic weight percentages and coating thicknesses were examined by X-ray. The transparent passivation after the Zn-Ni coating fully satisfied both adhesion and corrosion protection requirements for 321 and ML Black coatings. No red rust formation was observed on the coating samples after the test; only partial white rust formation was observed, and no peeling of the coating layer was detected in the adhesion tests. As a result, the optimum result of the passivation processes used for Geomet 321+ML Black coatings applied after the Zn-Ni + passivation process was obtained with transparent passivated Zn-Ni coatings. Even after 1200 hours, no red rust was observed in passivated Zn-Ni coating+ Geomet 321+ Geomet ML Black.

Introduction of Heavy Micro‐Titanium‐Carbide Particles into Zn–Ni Coatings on Steel During In Situ Brush Electroplating

The heavy micro‐titanium‐carbide (TiC) particles are first introduced into brush‐electroplated Zn–Ni coating (TiC‐0 coating) by using some surfactants here. The effect of TiC concentration of brush‐electroplating solution on the properties of Zn–Ni–TiC coatings is investigated. It is found that the coating hardness and corrosion resistance are enhanced significantly due to the co‐deposition of TiC and an optimal coating with a thickness of 71 μm and adhesive strength of 37.2 MPa is obtained when TiC concentration was 40 (g L−1) (TiC‐40 coating). The pencil hardness of TiC‐0 and TiC‐40 is 2 H and 5 H, respectively. The corrosion resistance time to hot NH4NO3 solution (or inferred neutral salt spray) of TiC‐0 and TiC‐40 are 40 and 240 min (or 321 and 1995 h), respectively. Many pores appear on the coating due to the incomplete overlap of many batch layers. The TiC content is the factor dominating the coating hardness and corrosion resistance by changing the structure, contact angle, and pore diameter of coating, thereby changing the linear polar resistance Rp from potentiodynamic polarization curves, charge‐transfer resistance Rct or |Z|0.01 Hz, or polarization resistance from electrochemical impedance spectroscopy. The content of Zn–Ni alloy is the factor dominating the adhesive strength of Zn–Ni–TiC coating.

Exploring the Effect of Microstructure and Surface Recombination on Hydrogen Effusion in Zn–Ni‐Coated Martensitic Steels by Advanced Computational Modeling

Ultrahigh‐strength steel (UHSS) structures are plated with Zn–Ni coatings because of their excellent corrosion resistance properties, but the plating process is accompanied by the production of hydrogen. The presence of hydrogen in steel results in hydrogen embrittlement. Hence, during the production of UHSS parts, dedicated outgassing steps are employed to remove the diffusible hydrogen from the steel. In a production environment, the real effect of the outgassing process and the outgassing efficiency is unknown for parts coated with Zn–Ni. Hence, a finite element model is developed to capture the evolution of the hydrogen concentration profile in coated UHSS parts during outgassing to study the influence of coating morphology and microstructural features of steel. In order to develop the geometry of the model, scanning electron microscope images are analyzed to understand the microstructure and morphology of the coating. Numerical samples are generated by combining different coating morphologies with steel substrates of varying microstructural features to attain a series of samples with varying features. The results of the outgassing simulations clearly demonstrate the major role of the coating morphology on the hydrogen flux.

Response surface analysis of Zn–Ni coating parameters for corrosion resistance applications: a Plackett–Burman and Box–Behnken design of experiments approach

AbstractThe development of cost-effective coatings with exceptional corrosion resistance is an ongoing challenge in the field of materials science. Among the promising coatings, zinc–nickel (Zn–Ni) coatings have shown great potential, especially when produced using economical electroplating technology. However, achieving optimal performance while minimizing coating thickness remains a complex task. In this study, the behavior of the responses was investigated according to the coating standards and levels, focusing on eight variables including temperature, time, cathodic current density, nickel concentration, substrate hardness, roughness, cathode–anode distance, and magnetic stirring speed. Four responses were investigated: coating thickness, roughness, microhardness, and corrosion rate with potentiodynamic polarization, using two design of experiments (DOE) methods: Plackett–Burman design (12 runs) and response surface methodology with Box–Behnken design (15 runs). The results show the degree of influence of each variable on the responses and their contribution to changing the responses. Additionally, response surfaces have been determined and it is shown that large response values can be achieved with small thicknesses. The morphological study using SEM, EDX, and XRD techniques revealed that the deposition conditions play an important role in the surface morphology. Some samples showed microcracks, while others had small grain size and were free of cracks and pores. Overall, this study provides new insights into the improvement of Zn–Ni coatings with exceptional corrosion resistance and cost-effectiveness.

Nickel partitioning in ZnNi coatings (Ni less than 4 wt.%) and its effect on the coating corrosion behaviour

ABSTRACT ZnNi alloy coatings with low Ni content (1–4 wt.% Ni) were electrodeposited over mild steel. Ni addition changed the coating morphology from faceted to hillock, decreased the crystallite size, and shifted the basal plane texture to higher energy (011) texture. Zn-1.5 wt.% Ni coating exhibited significantly improved corrosion resistance, even better than the pristine Zn coating. The corrosion resistance properties, however, degraded considerably as the Ni content increased (2.7 and 3.7 wt% Ni). The high corrosion resistance of the Zn-1.5 wt.% Ni coatings was due to the presence of nearly basal texture, low coating strain and evolution of stable γ-phase in the Zn matrix. The corrosion rate for higher Ni addition increased due to high energy surface texture and higher coating strain.

Effect of Deposition Potential on ZnNi Coating Corrosion Behaviour

ZnNi coatings were deposited using the electrochemical deposition method. In this study, the effect of potential electrodeposition on deposited properties, morphology, and size of ZnNi alloy nanoparticles was investigated in detail. The as-synthesized products were characterized by ZnNi coating properties is characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). The result indicated that the electrodeposition processes of ZnNi were governed by a nucleation process controlled by diffusion. XRD results showed that the phase structure of both alloy and composite coatings was single ZnNi phase. Potential increase influences the larger crystal size and the surface of coating was compact and uniform, the Rct increase, and greater the icorr so that the possibility of corrosion is higher.

Quantitative power spectral density analysis of nano/microstructured Ni-Zn electrodeposit and its correlation with superhydrophobicity

This paper aims to establish a quantitative relationship between wettability and surface morphology. The wettability of surfaces is highly dependent on surface morphology, and this relationship will be explored using either conventional roughness parameters or power spectral density (PSD) derived parameters. To investigate the effect of surface morphology on wettability, various Ni-Zn coatings with different hierarchical surface morphologies were electrodeposited on copper substrates. The coatings exhibited hydrophobic behavior with apparent contact angles ranging from 105° to 155°, depending on the shape, size, and arrangement of their surface features. Although conventional roughness parameters like Sq and Spc influenced the wettability of the coatings, their absolute values could not accurately predict superhydrophobic behavior. Therefore, the PSD analysis was used as an alternative approach to predict the wettability behavior of the coatings by distinguishing between nano- and micro-features. The results revealed that a superhydrophobicity (SH) index could be obtained from the PSD model to predict superhydrophobic properties. Coatings with an SH index below 0.32 exhibited a contact angle greater than 150°, regardless of their deposition parameters. The findings suggest that surface roughness plays a significant role in controlling the wettability of Ni-Zn coatings, and the SH index is a useful tool for predicting the superhydrophobic properties of these coatings.

Effects of niobium pentoxide nanoparticles on the tribological properties of electrodeposited ZnNi coatings

Electrodeposited ZnNi coatings are widely used to improve the corrosion resistance of steel substrates, but their tribological properties are also relevant for loaded contacts under relative motion. This work investigates the hypothesis of improving tribological properties of electrodeposited ZnNi coatings via dispersion of niobium pentoxide nanoparticles (1 g l−1) in the electrolytic bath. The niobium pentoxide nanoparticles were produced via hydrothermal synthesis assisted by microwave. The surface morphology and chemical composition of the coatings were analysed by scanning electron microscopy coupled with x-ray dispersive energy, X-ray diffraction and x-ray photoelectron spectroscopy. The tribological performance of the coatings was assessed using dry reciprocating ball-on-flat tests at normal loads between 3 and 6 N. The use of niobium pentoxide nanoparticles resulted in significantly denser coatings, with some Nb incorporated in the coated surfaces. Under the lowest normal load, all coated specimens showed relatively low friction (∼0.2) and negligible damage. As the normal load increased, the coating produced using niobium pentoxide nanoparticles showed stronger adherence, while conventional ZnNi coating showed increased friction and spalling for the highest load. It is believed that the Nb2O5 nanoparticles increased the number of sites for heterogeneous nucleation, refining the microstructure, so that tougher and more adherent coatings were produced.

The Performance of Zn-Ni Alloy Coating Electrodeposited from Stabilized Bath

A metallic part corrodes when it undergoes electrochemical reactions which cause the surface and structural deterioration of the metal. Through electroplating, metallic components can be protected from corrosion by coating them with Zn-Ni alloys. This study examined the electrodeposition of a Zn-Ni alloy film on a steel substrate from a chloride bath containing ethylene-diamine-tetraacetic acid (EDTA). A Pourbaix diagram using the OLI software was used to determine the stability of the Zn-Ni plating bath and the suppression of hydrogen evolution reaction (HER). Comparing the composition of Zn-Ni coating deposited in the EDTA bath with the pure Zn-Ni coating, the EDTA bath yielded higher deposition thickness and an average crystallite size reduction. The Zn-Ni coating deposited from the EDTA bath has a lower dissolution rate and better corrosion resistance properties than the non-EDTA bath. Polarization tests exhibited that the Zn-Ni alloy deposited from 0.119 mol/l EDTA bath at 20 mA/cm2 current density showed lower corrosion current (Icorr) and more positive corrosion potential (Ecorr). Atomic force microscopy (AFM) and Vickers microhardness testing were used to characterize the morphological properties, topographic structures, and microhardness of Zn-Ni coatings.

Effect of Ni Concentration on the Surface Morphology and Corrosion Behavior of Zn-Ni Alloy Coatings

This research work aims to develop electrodeposited Zn-Ni alloy coatings with controlled dissolution tendencies on a mild steel substrate. The varying Ni concentration in the electroplating bath, i.e., 10, 15, 20 and 25 g·L−1, affected the surface morphology and electrochemical properties of the deposited Zn-Ni alloy coatings. SEM and EDS analysis revealed the resulting variation in surface morphology and composition. The electrochemical behavior of different coatings was evaluated by measuring the open circuit potential and cyclic polarization trends in 3.5 wt.% NaCl solution. The degradation behavior of the electrodeposited Zn-Ni coatings was estimated by conducting a salt spray test for 96 h. The addition of Ni in the coating influenced the coating thickness and surface morphology of the coatings. The coating thickness decreased from 38.2 ± 0.5 μm to 20.7 ± 0.5 μm with the increase in Ni concentration. Relatively negative corrosion potential (<−1074 ± 10 mV) of the Zn-Ni alloy coatings compared to the steel substrate (−969 mV) indicated the sacrificial dissolution behavior of the Zn-rich coatings. On the other hand, compared to the pure Zn (26.12 mpy), ~4 times lower corrosion rate of the Zn-Ni coating (7.85 mpy) was observed by the addition of 25 g·L−1 Ni+2 in the bath solution. These results highlighted that the dissolution rate of the sacrificial Zn-Ni alloy coatings can effectively be tuned by the addition of Ni in the alloy coating during the electrodeposition process.

Influence of laser surface structuring of steel sheets on the mechanical properties of electrodeposited ZnNi coatings

The influence of laser surface structuring on the formation and the internal strength of electrodeposited ZnNi coatings on steel sheets was investigated. Surface structuring by extended direct laser interference patterning (xDLIP) was used to modify the cohesive strength in the ZnNi layer. An SEM analysis of the crystal structures shows perpendicular nucleation during ZnNi layer formation and areas of crosslinked crystalline structures, which results in an interlocking of crystal structures within the layer. The interlocked crystalline structure leads to an increase of the cohesive strength in the ZnNi layer, which was observed in roller peel tests according to DIN 1464 for adhesively bonded joints.

Hydrogen absorption rate and hydrogen diffusion in a ferritic steel coated with a micro- or nanostructured ZnNi coating

This study investigates the effect of the microstructure of electrodeposited ZnNi coatings, in particular pores and microcracks, on hydrogen diffusion characteristics at room temperature. The hydrogen permeation behavior and thermal desorption spectra of electrodeposited ZnNi micro- and nanostructured coatings were studied and compared. The microstructures of the coatings were observed using a scanning electron microscope. The results showed that the presence of microcracks significantly influences the hydrogen diffusion behavior: in microstructured ZnNi hydrogen can diffuse along the microcracks due to the large number of microcracks present, leading to higher hydrogen absorption during electrochemical charging. Also, the high grain boundary density in the nanostructured coating leads to the presence of a larger number of strong H traps, and thus lower diffusible H content.

Sacrificial Zn–Ni coatings by electroplating and hydrogen embrittlement of high-strength steels

Abstract A review of sacrificial Zn–Ni electroplating coatings on high-strength steels is presented. These steels are used for heavy structural applications such as landing gears, etc., that are subjected to high stresses and corrosive environments in service. The electroplating process involving aqueous electrolytes invariably produces hydrogen. The emitted hydrogen can diffuse into substrate steel, contributing to the delayed failures by hydrogen embrittlement. Microstructural inhomogeneities arising from the heat treatments and defects produced during coatings and those inherently present in the steels can trap hydrogen emitted during plating. Dissolved and trapped hydrogen can slowly diffuse to the stress concentrations or crack tips, contributing to the delayed structural failures. Baking after plating helps to eliminate hydrogen to some extent, though it may introduce some thermomechanical stresses at the bimaterial interfaces. This review discusses a) the current state of sacrificial Zn–Ni coatings, b) their protection against corrosion of the substrate, c) the associated hydrogen embrittlement predominately under cyclic loads, and d) recent advances in terms of the compositionally modulated coatings for enhanced protection.

Fatigue Analysis of Threaded Components with Cd and Zn-Ni Anticorrosive Coatings

The influence of the electrodeposition of cadmium and zinc-nickel and the stress concentration effect on the fatigue behavior of AISI 4140 steel threaded components were studied. Axial fatigue tests at room temperature with a stress ratio of R = 0.1 were performed using standard and threaded specimens with and without nut interface under base material, cadmium, and zinc-nickel-coated conditions. Finite element analysis (FEA) was used, considering both elastic and elastoplastic models, to quantify the stress distribution and strain for threaded specimens with and without a nut interface. The numeric results were correlated to the experimental fatigue data of threaded components with and without the nut interface, to allow the oil & gas companies to extrapolate the results for different thread dimensions, since the experimental tests are not feasible to be performed for all thread interfaces. Scanning electron microscopy (SEM) was used to analyze the fracture surfaces. The stress concentration factor had a greater influence on the fatigue performance of threaded components than the effect of the Cd and Zn-Ni coatings. The fatigue life of studs reduced by about 58% with the nut/stud interface, compared to threaded components without nuts. The elastoplastic FEA results showed that studs with a stud/nut interface had higher stress values than the threaded specimens without a nut interface. The FEA results showed that the cracks nucleated at the regions with higher strain, absorbed energy, and stress concentration. The substitution of Cd for a Zn-Ni coating was feasible regarding the fatigue strength for threaded and smooth components.

Effect of brush plating process variables on the microstructures of Cd and ZnNi coatings and hydrogen embrittlement

Brush plated ZnNi coating is evaluated for replacement of Cd coating during repair of sacrificial coatings on high strength steel components. Plating parameters such as deposition voltage, surface preparation and type of anode for coating deposition are used to study the risk of Internal Hydrogen Embrittlement (IHE). Coating characterization using Transmission Electron Microscopy (TEM) is correlated with Incremental Step Load (ISL) testing, permeation measurements and Thermal Desorption Spectroscopy (TDS) to evaluate the effect of microstructure and crystallographic defects within the coating on the risk of internal hydrogen embrittlement (IHE) of the substrate steel. It is observed that the coating microstructure plays an important role in mitigating IHE. Brush plated ZnNi coatings at 6 V deposition voltage with grit blast method of surface preparation and graphite anode, or deposition at 12 V with scotch-brite™ method of surface preparation and either of platinized Ti or graphite anode can suitably replace Cd coating. Presence of twin boundaries within the coating proved to be beneficial to decrease the risk of IHE by minimizing the H diffusion to the substrate. On the other hand, stacking faults and dislocations within the ZnNi coating do not sufficiently trap hydrogen and therefore do not mitigate the IHE risk when plated at 10 V and 12 V. Coating deposited at 6 V generates low amount of hydrogen, and does not cause IHE irrespective of the microstructure. TDS measurements performed to quantify the hydrogen desorption from different plating conditions indicate a direct correlation between the amount of hydrogen generated during plating and degradation of mechanical strength by IHE cannot always be established, principally because of the influence of microstructure.

Anodic degradation of Zn-Ni coatings in moderately alkaline NaCl solution

Carbon steel samples covered with initially crack-free zinc-nickel coatings were polarized with a small anodic overpotential in moderately alkaline NaCl solution. Along with zinc dissolution, the coatings developed a mud-crack pattern due to tensile stress release, allowing the electrolyte to access the underlying steel surface. Simonkolleite grew on both the zinc-nickel coating and the steel substrate. The resulting current density, that was first strongly anodic, switched to small cathodic values when the coating surface was almost fully covered by a compact simonkolleite layer.