Fabrication of Ni–ZrO₂ nanocomposites through a new electroforming bath and Assessment of their morphology, wear, and corrosion resistance

Abstract

Nowadays, researchers are looking for ways to produce complex tools and pieces with high precision at a low cost. In recent decades, electroforming has been an important and stable technique for producing composite parts. In this research, Ni–ZrO₂ nanocomposite foils were fabricated by using a nickel-chloride bath through electroforming, a bath not previously utilized for this purpose. In this study, the effects of ZrO₂ concentration and direct current density on the volume percentage of ZrO₂ nanoparticles and the grain size of the nickel matrix of foils are also investigated. The sample with 13.65 vol % nanoparticles had the highest volume percentage and the minimum nickel grain size of 516.9 nm, which is almost 46 % smaller than the grain size of pure nickel foil. The wear and corrosion behavior of the foils were examined using a pin-on-disk wear test, potentiodynamic polarization, and impedance spectroscopy analysis. The results showed considerable improvement in the wear and corrosion resistance of the Ni–ZrO₂ samples compared to the pure electroformed nickel. The nanocomposites exhibit a lower friction coefficient than pure nickel, with a maximum reduction of 44 %. A composite specimen of Ni–ZrO₂ had 2.5 % lower corrosion density and 596 % higher charge transfer resistance compared to pure nickel. It was concluded that the nickel-chloride bath has an excellent potential to produce composite nickel foils with acceptable brightness, satisfactory wear, and corrosion resistance.

Graphical abstract

Highlights

• •A new, economically simple electroforming bath (nickel-chloride) was used successfully to fabricate Ni–ZrO₂ composites.
• •Higher ZrO₂ vol. % and finer nickel crystals in the Ni-matrix were directly related to the amount of ZrO₂ in the bath and the direct current density.
• •The increase in current density led to more uniformity of the nano-particle distribution and smaller nickel crystals.
• •Adding ZrO₂ nanoparticles to nickel composite foils increased wear resistance, reduced friction coefficient, and changed the wear mechanism to more abrasive behavior.
• •The addition of ZrO₂ nanoparticles resulted in lower corrosion current density, a less negative corrosion potential, and higher charge transfer resistance.

1. Introduction

As society and industry grew, researchers realized that existing materials could not meet all demands. To address this, they began creating composites by combining the properties of different materials in a way that mimics nature. It's worth noting that composite materials have been used throughout human history, but only recently has scientific analysis of their foundations become more accurate. A composite is a material made by combining different components with varying properties to achieve a final product with specific different properties. The production and development of new composite materials with high hardness, wear resistance, and favorable corrosion behavior have gained considerable attention in various industrial applications, such as aerospace, automotive, biomedical, nuclear reactors, catalysts, and others [[1], [2], [3]]. Particle-reinforced composites in a metallic matrix that consist of two or more components with different properties can create or enhance new heterogeneous characteristics in the resulting material [4,5]. One of the most effective types of this kind of material is nickel-matrix composites which can be fabricated by various methods such as powder metallurgy, stir and squeeze casting, friction stir processing, and co-deposition electroplating [5,6]. Among these methods, electroforming which is based on the principles of electrodeposition has several advantages compared to other methods, such as low process costs, adequate control in particle distribution, the ability to produce highly detailed parts with complex shapes and fine details without the requirement for high temperature or pressure [[7], [8], [9]]. The co-deposition of nanoparticles in the electrodeposition process is a complex phenomenon influenced by various factors. While recent models have been developed to better describe the co-deposition of nanoparticles, the Guglielmi model [10] provides a fundamental framework for understanding the co-deposition of particles. One of the recent models is the "kinetic model" [11]. This model takes into account the thermal action of laser radiation on the electrodeposition process, which enhances the co-deposition of nanoparticles. It is reported that composite electrolytic coatings produced with laser stimulation of the deposition process are obtained by a higher concentration of particles in a coating of finer size due to the presence of a temperature gradient, which provides an additional supply of metal ions in the irradiation region. Another model is the mathematical-based approach [12]. This model uses a combination of theoretical and experimental approaches to describe the growth of layered double hydroxide (LDH) nanomaterials through electrodeposition. The model incorporates factors such as the electrolyte composition, the electrode potential, and the temperature to predict the growth kinetics and the structural properties of the deposited layers.

In this process, inert particles are suspended in an electrolyte solution and are embedded in the nickel matrix during electrolysis. The incorporated particles can be SiC, TiO₂, Al₂O₃, W, ZrO₂, WS_2, etc., which have been used so far [[13], [14], [15], [16], [17], [18]]. Literature suggests that incorporating Zirconia (ZrO₂) into nickel is an excellent choice, as it can improve nickel properties due to its chemical stability, high melting temperature, and resistance to corrosion and wear [19,20]. Additionally, to achieve good mechanical properties and surface morphology, it is crucial to adjust the electroforming operation parameters, such as bath composition, current density, ZrO₂ particle size and concentration, temperature, and pH [7,20,21]. Gul et al. [22] showed that the electrodeposition method can significantly affect the microstructure and tribological behavior of Ni–Al₂O₃ nanocomposite coatings. Xiong et al. [23] studied the microhardness and wear properties of nanocomposite Ni–ZrO₂ electroplated coatings with different ZrO₂ concentrations. He found that as the concentration of ZrO₂ powder in the solution raised, there was an initial reduction followed by an increase in the width of the wear track. Conversely, the hardness initially increased and then fell. Also, the mechanical characteristics of the Ni–ZrO₂ coatings were at their best when the concentration of ZrO₂ was maintained at 10 g/L. Arghavanian and Parvini [18] investigated the particle distribution and corrosion resistance of Ni–ZrO₂ composite Coatings. Also, they expressed that evaluation of corrosion behavior with increasing ZrO₂ content in the coating caused the corrosion potential to shift towards noble and positive values. Parida et al. [2] studied the wear resistance of Ni–ZrO₂ coating with different strengthening mechanisms obtained due to different deposition parameters in the watts bath. Jun et al. [7] produced the Ni-PSZ1 composite using the electroforming technique in a nickel-sulfamate bath. They concluded that the PSZ particle content in the composite coatings had a strong effect on the integrity of the nickel matrix and wear resistance.

Despite numerous investigations in this area, a good image of the effect of electroforming parameters on the microstructure and properties of the produced composites has yet to be established. The novelty of this study is producing Ni–ZrO₂ nanocomposite foils using an electroforming method and a cost-effective nickel-chloride bath [24] by Sodium Dodecyl Sulfate in the absence of commercial and expensive dispersant surfactants for the first time. The direct current density and ZrO₂ nano-particle concentration were varied to optimize the composite's properties. The main goal of the presented method and bath is to be used in manufacturing industrial components. Therefore, their mechanical properties and chemical resistance should be evaluated and found in the optimum possible condition. Thus, the study also investigated the corrosion behavior and wear resistance of pure nickel and Ni–ZrO₂ electroformed foils, along with the distribution and incorporation mechanism of ZrO₂ nano-particles.

2. Material and methods

The nickel-chloride bath which had been presented in previous research [24], was used for the electroforming of Ni–ZrO₂ composited foils in this work. The electroforming bath composition and process parameters to fabricate composited products are shown in Table 1. The process was carried out by using a direct current system. Cleaned and passivated 304 stainless steel samples of size 4 × 2.5 × 0.05 cm³ were used as the cathode and a nickel plate with a purity of 99.9 % with the size of size 4 × 2.5 × 0.05 cm³ was used as the anode. As shown in Table 2, the current density and concentration of nano ZrO₂ particles with average diameters of 70 nm were determined as variable parameters and they were varied from 1 to 3 A/dm² and from 0 to 3 g/L, respectively.

Table 1.

Electroforming bath composition and process parameters.

Nickel chloride (NiCl2·6H2O)	80 g/L	Merck company
Boric acid (H3BO3)	4 g/L	Merck company
Saccharine	0.3 g/L	Sigma-Aldrich
ZrO2nanopowder	0–3 g/L	Merck company
SDS	5.52 × 10−3 g/L	Merck company
Deionized Water	0.1 L
pH	4.5
Electroforming time	6 h
Current density	1–3 A/dm2
Temperature	45 °C
Magnetic stirring speed	200 rpm

Table 2.

Volume percentage of ZrO₂, Thickness of deposits, and nickel grain size of samples in different amounts of ZrO₂ content and current density.

	Volume percentage of ZrO2 (vol. %)	Nickel grain size (nm)	ZrO2 Nano-powder (g/L)	Current density (A/dm2)	Thickness (μm)
Ni-0	0	1127.4	0	1	75
Ni-1	5.165	1059	1	1	76
Ni-2	6.286	737.7	2	1	77
Ni-3	7.139	663.52	3	1	85
Ni-4	13.65	634.4	2	2	139
Ni-5	11.91	516.9	2	3	227

Preparation of the co-deposition bath was started by adding ZrO₂ nano-particles into the nickel-chloride bath and homogenizing for almost 10 min with an ultrasonic homogenizer. Then, a certain amount of Sodium Dodecyl Sulfate (SDS) as an anionic surfactant was added subsequently and mixed for 20 min. This step was intended to improve the uniformity and stability of nano-particle suspension in the bath. After dispersing the particles, the magnetic heater stirrer was applied to homogenize the bath continuously for 6 h until the end of the process. It is worth mentioning that the bath was prepared fresh for each electroforming process. The pH of the electroforming bath should remain constant. Accordingly, it was measured during the deposition and adjusted by adding Boric acid. After each process, the removed composite foils were dipped and cleaned ultrasonically in Acetone 96 % for 5 min. Fig. 1 illustrates the main production steps of the co-deposition electroforming procedure.

Fig. 1.

Schematic of the electroforming process steps to produce Ni– ZrO₂ composite,

(a) preparation of electroforming bath, (b) ZrO₂ dispersion mechanism with SDS surfactant, and (c) co-electrodeposition process.

2.1. Study on morphology and microstructure

A section of each sample was cut from the middle of each cross-section and their thicknesses (shown in Table 2) were measured by using Optical Microscope Images. The uniformity of reinforcement phase distribution and surface morphology of composite foils were examined using SEM TE-SCAN model Vega3 and FESEM model MIRA3 images. Also, the presence of Zr in the depositions was determined by the energy dispersive analyzer system (EDX) coupled with SEM. The average volume fraction of the nanoparticles in each composite sample was calculated using SEM images from the surface and cross-section of the samples and Image J analysis software. Moreover, X-ray diffraction analysis with Cu-kα radiation and Xpert High Score software was taken to confirm the presence of ZrO₂ particles and identify the microstructure phases and nickel grain size in each sample. The analysis was performed using a PHILIPS X-ray diffractometer model PW1730 under an angle range of 10–80°. The grain size was determined by using the Scherrer equation (1) Where D is the grain size, λ is the incident radiation, β is the corrected peak width at the half-maximum intensity and ϴ is the angular position [16].

$$D=\frac{0.9\lambda }{\beta \mathit{COS}\theta }$$ (1)

2.2. Wear test

The study on wear behavior was accomplished by pin-on-disk test based on the ASTM G99-05 standard [[21], [25]] and repeated three times for each specimen to determine the friction coefficient and wear resistance of pure electroformed nickel and Ni–ZrO₂ composite foils. The tests were performed at a constant load of 3 N with a chrome steel AISI 52100 pin, by rotational speed of 20 m/s, in a circular path with a 200 m total distance and 6 mm diameter. Before and after each wear process, the samples were ultrasonically cleaned in Acetone 96 % for 5 min. Also, their initial and final mass and density were measured to calculate the normalized volume loss percentage that was independent of the initial density. Finally, the worn surfaces of pure nickel and composite foils were analyzed by SEM images to investigate the influences of the process on surfaces and study the wear mechanism.

2.3. Electrochemical tests

The electrochemical behavior of pure electroformed nickel and Ni–ZrO₂ foils was studied in a 3.5 % NaCl electrolyte at the ambient temperature by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) based on ASTM G4 standard [26]. Both tests were performed by AUTOLAB device and their experimental data (including corrosion potential (E_corr), corrosion current density (i_corr), polarization resistance (R_p), solution resistance (R_s), charge transfer (R_ct), and n as an experimental parameter) were calculated and analyzed by Nova 1.7 and ZView analyzer software. The measurements were accomplished by Ag/AgCl reference electrode, platinum electrode, and electroformed samples as working electrodes. Before each test, the open circuit potential (EOCP) was investigated for a time of 1800 s. The potential sweep rate of the potentiodynamic polarization test, in anodic and cathodic direction was 1 mV/s and it was scanned from −0.3 to 0.3 vs OCP. The employed amplitude of impedance tests was 10 mV. The EIS test was performed at 50 frequencies in the frequency range of 10 mHz–100 KHz. The Nyquist curves were fitted and analyzed employing ZView software.

3. Results and discussion

Table 2 and Fig. 2 show the relationship between the ZrO₂ particle content in the electroforming bath and the volume percentage of ZrO₂ as a reinforcement in the nickel substrate. As Fig. 2 illustrates, the volume percentage of ZrO₂ in the nickel matrix increased with increasing ZrO₂ concentration in the bath from 0 to 3 g/L. Several studies have confirmed this result, stating that as the inert particle content increases in the electrolyte, more particles are absorbed on the cathode surface [27]. However, this rapid increase process continues until the particle concentration reaches a saturation point, where the suspended particles in the bath become agglomerated and the number of embedded particles in the substrate decreases [27].

Fig. 2.

The relationship between the volume percentage of ZrO₂ in Ni– ZrO₂ composites

(a) ZrO₂ particle content and (b) current density.

According to the literature [10,28,29] and based on Guglielmi's theory, the process of inert particle distribution into a metallic matrix takes place in three steps (1) loose adsorption, (2) strong adsorption and (3) embedding into the metal substrate. According to this mentioned theory, dispersed ZrO₂ nano-particles were transferred from the bulk of the suspension to the surface of the cathode, by mechanical movement due to the stirring of the solution. In the second step, the particles were absorbed into the nickel matrix due to the strong electrical attraction force of the Helmholtz double layer on the cathode surface. Finally, the absorbed particles were embedded between reduced metal grains. In a direct current field, charged particles in the solution migrated electrophoretically and were drawn to the opposite electrode. In addition, empirical evidence has demonstrated that ZrO₂ nano-particles with negative surface charge exhibit superior incorporation efficiency into the metal matrix than those with positive charge [27].

Fig. 3 illustrates the mechanism of the co-deposition process of Ni–ZrO₂ composited foil in the presence of SDS as an anionic surfactant. When the co-deposition process began, primary Ni²⁺ preferred to transfer and absorb onto the cathode, while some Ni²⁺ surrounded the negatively charged ZrO₂ particles which had been modified by the ionic SDS while the negative charge of SDS causing repulsion between particles and dispersed them in the electroforming bath. Therefore, it was investigated that the main components of the suspension and incorporation process of ZrO₂ particles into the nickel substrate during the electroforming process were the following steps [28,30].

• -Transfer of the primary Ni²⁺ ions from the bulk of the solution to the cathode by Coulomb force;
• -Formation of anionic SDS clouds around some ZrO₂ particles;
• -Transfer and adsorption of charge-free and modified particles to the nickel substrate by mechanical action and electrophoretic migration, respectively;
• -Incorporation of nano-particles into the reduced nickel atoms by random entrapment or Van der Waals forces.

Fig. 3.

Schematic representation of the co-deposition mechanism of Ni–ZrO₂ composite

during the electroforming process.

The electroformed composites of ZrO₂ were achieved under the condition of 45 °C temperature, 4.5 pH, 6 h electroforming time, and 5.52 × 10⁻³ g/L SDS as the constant and optimal parameters while the ZrO₂ content and the current density were varied according to Table 2. Also, the average grain size of the nickel matrix and the ZrO₂ volume percentages were determined based on these mentioned variables. It was mentioned that the volume percentage of ZrO₂ nano-particles in the electroformed nickel increased rapidly when the concentration of ZrO₂ in the bath increased. In another hand, based on Fig. 2-b, an increase in current density had the same effect [27,31] on the volume percentage of ZrO₂, from 6.286 vol % to 13.65 vol % by using 1 A/dm² and 2 A/dm² current densities, and then decreased slightly to 11.91 vol % in further amounts. At the current density of 3 A/dm², the electrical attraction between the surface of the cathode and Ni²⁺ improved. In other words, the tendency and mobility of nickel ions towards the cathode were higher and faster than those of nano-particles, as their migration from suspension towards the cathode was mainly carried out by the mechanical stirring force. Therefore, increasing the rate of reduction and deposition of nickel led to a decrease in the chance of integrating nano-particles into the nickel substrate [28,32,31]. Fig. 4 displays the appearance and shape of pure and Ni–ZrO₂ composite foils. Pure nickel foil had a smoother and brighter surface compared to the foil containing nano-particles which had a white/silver color due to the suspended ZrO₂ particles.

Fig. 4.

The appearance and shape of nickel electroformed products were achieved

under different conditions of ZrO₂ content and the current density.

The results in Fig. 5-b indicate that the grain size of the nickel substrate decreased due to an increase in the current density and the ZrO₂ volume percentage in the composite foils. The largest grain size belonged to pure nickel, which was 1127.4 nm, and it decreased to 516.9 nm in the composite sample that was produced by 2 g/L ZrO₂ concentration and 3 A/dm² of current density. The current density had an important and complex effect on the nickel grain size, which depended on various factors related to the electroforming process. Some of these factors were the different bath compositions, which determined the concentration and mobility of nickel ions and additives in the solution, the electrochemical reactions that took place at the cathode surface, such as the reduction of nickel ions and the evolution of hydrogen bubbles, and the surface condition of the cathode [[29], [30], [32], [31]]. In general, these factors affected the availability of nickel ions for nucleation and growth of clusters, as well as the morphology and structure of the electroformed layers. As shown in Table 2 and Fig. 5, at high current densities, the grain size of nickel deposits decreased due to the mass transfer limitation of nickel ions from the bulk of solution to the cathode surface, which could not keep up with the high reduction rate of Ni²⁺. This increased the nucleation rate and decreased the growth rate of nickel grains. Also, the changes in the surface energy and growth mechanism in the presence of hydrogen bubbles evolution caused a decrease in the nickel grain size by increasing current density [20]. Moreover, the presence of nano-particles had a similar effect on the nickel grain size. The surfaces of ZrO₂ acted as nucleation sites for nickel grains and provided new regions for nucleation in the co-deposition process, compared with pure nickel deposition [33,34]. Therefore, by reducing nickel ions on the cathode surface, ZrO₂ particles simultaneously existed at the nickel grain boundaries, stopped their growth, and made the nickel grain size smaller.

Fig. 5.

The relationship between nickel grain size in Ni– ZrO₂ composites

(a) ZrO₂ particle content and (b) current density.

Fig. 6-(a) shows the surface morphology of a pure nickel electroformed sample, and Fig. 6-(b to f) shows the surface structure and ZrO₂ incorporation content of composited foils with different ZrO₂ concentrations and current densities. As shown in Fig. 6-(a), the pure nickel foil had a smooth, uniform surface with larger and more compact grains than the Ni–ZrO₂ electroformed foils. In contrast, the composited samples had fewer uniform surfaces with spherical and smaller-sized grains, as well as some micro-cracks and voids that resulted from the distortion and strain fields around the embedded nano-particles. Moreover, it is important to note that the surface grain size is related to the grain size, but it is usually bigger than the grains. In other words, each spherical or columnar grain is composed of several smaller metallic grains [35].

Fig. 6.

SEM and FE-SEM micrographs of (a) pure nickel foil at 5000x, (b) Ni-1 at 10000x, (c) Ni-2 at 10000x, (d) Ni-3 at 10000x, (e) Ni-4 at 50000x and (f) Ni-5 at 50000x, and (h) EDX result of sample Ni-3, the yellow circles were some points where the Zr was detected. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 7 shows the XRD patterns of pure nickel and composited sample Ni-3, which was produced by 1 A/dm² of current density and contained 7.139 vol % ZrO₂ nano-particles. the XRD patterns of pure nickel and composited sample Ni-3. The presence of ZrO₂ nano-particles in sample Ni-3 was confirmed by XRD patterns which was consistent to the EDX result, as recorded in Fig. 5-h. The XRD peaks of the composited foil were more intense than those of pure nickel, due to the incorporation of ZrO₂ nano-particles into the nickel substrate, as reported in other works [16,20]. The calculated results also indicated that the nickel texture orientation was along (111), (200), and (220) crystallographic planes, while the Ni–ZrO₂ foil exhibited additional orientations of (002), (220) and (−111), which corresponded to ZrO₂ nano-particles on the nickel matrix.

Fig. 7.

XRD pattern of electroformed pure nickel and Ni–ZrO₂ sample Ni-3.

3.1. Wear behavior

Table 3 shows the wear test data, the mean friction coefficient, and the volume loss percentage for pure and composite nickel foils in each wear test. The importance of the wear test is that Wear-resistant components can maintain their structural integrity and functionality even under high-stress conditions, ensuring consistent performance and reliability. This is particularly important in industries where downtime can result in significant losses, such as aerospace, energy, high-speed machinery, or critical infrastructure. The results indicated that the pure electroformed nickel had the highest friction coefficient [[36], [37], [38], [39]] and it was decreased in Ni–ZrO₂ composites due to the addition of ZrO₂ nano-particles. This reduction of friction coefficient in composite foils showed an improvement in wear resistance because of a significant change in the wear mechanism and an increase in the hardness and strength of the nickel matrix [19,40,41]. However, despite the enhanced wear resistance of composite samples due to the presence of ZrO₂ nano-particles, the mass loss percentages in samples Ni-1, Ni-2, and Ni-3 were higher than that of pure nickel. Part of the volume loss was due to the wear of ZrO₂ particles, not just nickel deposits. Fig. 8 illustrates the relationship between the mean friction coefficient and ZrO₂ content (vol. %). The composite sample Ni-5, reinforced with 11.91 vol % of ZrO₂ particles, exhibited the lowest mean friction coefficient (1.056) and volume loss percentage (0.52 %), and the highest wear resistance. Above 11.91 vol %, ZrO₂ nano-particles (sample Ni-4 with 13.65 vol % of ZrO₂) tended to agglomerate and reduce the mechanical properties of the nickel substrate against the wear process. Conversely, the highest friction coefficient (2.399) and volume loss percentage (2.23 %) belonged to the pure nickel sample Ni-0 and the composite sample Ni-1, respectively. Many studies have investigated the effect of nano-particle dispersion on the strengthening mechanism in wear conditions. It was observed that the incorporation of ZrO₂ particles into the Ni matrix made a change in the wear mechanism from adhesive to abrasive form [32,40,41].

Table 3.

Variation of average friction coefficient and average volume loss percentage in pure and Ni–ZrO₂ composites affected by volume percentage of ZrO₂.

	Volume percentage of ZrO2 (vol. %)	Average Friction coefficient	Average Volume loss (%)
Ni-0	0	2.399	1.4
Ni-1	5.165	2.104	2.23
Ni-2	6.286	1.867	1.55
Ni-3	7.139	1.581	2.02
Ni-4	13.65	1.208	0.55
Ni-5	11.91	1.056	0.52

Fig. 8.

Variation of friction coefficient of pure Ni and Ni–ZrO₂ composites with different

volume percentages of ZrO₂.

According to the literature, the wear behavior of particle-reinforced composites during the pin-on-disk wear test consists of four steps [32]. In the first step, the initial and soft interaction between the reinforcing particles on the surface of the composite and the abrasive pin occurs. Then, the contact area between the composite and the steel pin increases, which exposes the metallic matrix. Meanwhile, due to the damage on the surface of the pin, the wear process intensifies. The third step involves both adhesive and abrasive mechanisms that occur simultaneously. However, the proportion of each mechanism depends on the percentage of the reinforcing phase and the grain size of the matrix. In the abrasive mechanism, the wear process continues with the complete or partial removal of the particles from the surface of the composite.

Fig. 9 shows removed particles and wear tracks of composite sample Ni-3. The removed particles can move freely on the substrate or be embedded on the pin surface and create shallow grooves on the composite surface along with the pin movement. On the other hand, adhesive wear occurs by embedding and pressing particles into the matrix, which leads to the connection between the surface of the matrix and the abrasive pin. In this situation, the pin movement causes plastic deformation, deep grooves, ploughing, spalling pits, and delamination of the matrix. These two mechanisms proceed layer by layer on the composite surface and when the initial surface is smoothed, the wear of the subsequent layer begins. Fig. 10 shows the morphology of pure nickel and Ni–ZrO₂ composites which illustrate abrasive and adhesive wear effects.

Fig. 9.

Removed ZrO₂ particles (the size of some particles has been mentioned) and wear tracks of worn composite sample Ni-3.

Fig. 10.

SEM morphologies of the wear tracks of (a) pure nickel and composite samples (b) Ni-3, (c) Ni-4, and (d) Ni-5. (The mentioned numbers indicate (1) adhesive wear, (2) ploughing, (3) delamination, (4) peeling of particles, (5) plastic deformation, (6) abrasive wear, (7) row of grooves, (8) wear track and (9) removed particle.).

The wear resistance of Ni–ZrO₂ samples was found to be higher than pure nickel due to less destructive wear and plastic deformation by the adhesive wear mechanism and more shallow tracks and grooves by abrasive wear. The results showed that the hardness of the samples, surface morphology, ZrO₂ content, and distribution influenced the wear mechanism and resistance. This is supported by Fig. 10.

Fig. 11 presents the friction coefficient curves versus sliding distance for pure nickel and Ni–ZrO₂ foils. The friction coefficient curve of pure electroformed nickel had a higher amplitude of fluctuation than composited foils which proved that pure nickel was more destructive and had lower wear resistance.

Fig. 11.

Plot of wear distance versus friction coefficient of (a) pure Ni, (b) Ni-1 (5.165 vol % of ZrO₂), (c) Ni-2 (6.286 vol % of ZrO₂), (d) Ni-3 (7.139 vol % of ZrO₂), (e) Ni-4 (13.65 vol % of ZrO₂) and (f) Ni-5 (11.91 vol % of ZrO₂).

3.2. Corrosion behavior

The electrochemical corrosion tests were taken to evaluate the corrosion resistance behavior of the deposits. Table 4, Table 5 show data calculated from potentiodynamic polarization curves and electrochemical impedance spectrum, respectively. Fig. 12 shows the potentiodynamic polarization curves of pure Ni and Ni–ZrO₂ composited electroformed foils, and Tofel plots show an active-passive transition for all electroformed samples. Based on these results, it is clear that the presence of ZrO₂ particles in the nickel matrix caused a shift in corrosion potentials towards positive values, a decrease in corrosion current densities, and an improvement in corrosion resistance of composited foils compared to pure nickel. The corrosion behavior of the composite materials is mainly determined by their chemical and phase constitution and microstructural features such as grain size and surface topography. Also, the homogeneous distribution of inert particles and their interfaciality with the metallic matrix significantly influence the corrosion characteristics [42]. Therefore, the corrosion potential of the obtained composites varied with the ZrO₂ content (vol. %) and nickel grain size.

Table 4.

Parameters derived from potentiodynamic polarization curves for pure Ni and Ni–ZrO₂ electroformed samples.

	icorr (μA/cm2)	Ecorr (V vs Ag/AgCl)	Rp (kΩ.cm2)
Ni-0	5.27	−0.446	2.154
Ni-1	2.85	−0.432	4.654
Ni-2	0.201	−0.165	125.61
Ni-3	0.130	−0.131	111.96
Ni-4	0.441	−0.319	49.19
Ni-5	0.465	−0.308	36.49

Table 5.

Parameters derived from electrochemical impedance spectrum and Nyquist diagram for pure Ni and Ni–ZrO₂ electroformed samples.

	Rs (Ω.cm2)	Rct (Ω.cm2)	CPEdc (μF.cm−2)	n
Ni-0	11.68	9135	22.48	0.965
Ni-1	11.75	14471	21.50	0.863
Ni-2	19.3	48504	2.494	0.954
Ni-3	14.76	54499	2.482	0.850
Ni-4	11.12	23913	10.65	0.862
Ni-5	10.79	33211	10.79	0.865

Fig. 12.

Potentiodynamic polarization curves for pure Ni and Ni–ZrO₂ composites in various volume percentages of incorporated ZrO₂.

Sample Ni-3 had the lowest corrosion current density (0.130) and the least negative corrosion potential (−0.131), which was produced under 1 A/dm² with 7.139 vol % of ZrO₂ and 663.52 nm of grain size. Higher ZrO₂ content than 7.139 vol % and finer nickel grain than 663.52 nm raised the corrosion current density and worsened the corrosion resistance in samples Ni-4 and Ni-5, as shown in Fig. 13. The incorporated ZrO₂ contents as inert sites and physical barriers exhibited good resistance behavior to the corrosive chloride environment [[42], [43]]. However, higher values of ZrO₂ (especially in agglomerated form) could act as high energy and corrosion active sites [30,41]. Also, as mentioned before, the larger amount of ZrO₂ content and direct current density resulted in smaller nickel grain size and broad grain boundary, which played a prone path for corrosion [31]. In addition, Liu et al. [44] reported that a considerable decrease in grain size can lead to initiating unstable sites on the surface of the samples which raises the possibility of local corrosion and caused to make pits. Although some observations indicate that whenever the position of pitting is on the boundaries of an oxide particle, or it grows up directly to be stopped by an inert oxide particle, subsequently the dissolution of the sample can be limited [44,45].

Fig. 13.

Variation of corrosion current density of pure nickel and Ni–ZrO₂ composites with (a) different

volume percentage of ZrO₂ and (b) different nickel grain sizes.

The corrosion behavior of Ni–ZrO₂ electroformed samples was also examined using the EIS technique for the same immersion time and open circuit potential. The impedance data in the form of Nyquist curves are presented in Fig. 15. The impedance data of all samples can be described using the electrical equivalent circuit model (EEC) consisting of a resistor and a capacitor connected parallel, illustrated in Fig. 14. The resistor stands for the charge transfer resistance and the capacitor represents the electrochemical double layer. The calculated amounts of all EIS parameters, the double layer constant phase element (CPE_dc), charge transfer resistance (R_ct), electrolyte resistance (R_s), and n value as an experimental parameter that indicates the surface roughness of the working electrode, are tabulated in Table 5.

Fig. 15.

Nyquist impedance curves for pure Ni and Ni–ZrO₂ composites in various volume percentages of incorporated ZrO₂.

Fig. 14.

Model of the equivalent circuits propose for curve fitting of the EIS data for electroformed pure Ni

and Ni– ZrO₂ samples.

The amount of n is between 0 and 1 and as the surface roughness of the work electrode increases, the n value tends to 0. As seen in Fig. 15 all the Ni–ZrO₂ composites exposed higher charge transfer resistances compared to pure nickel. The results indicated that charge transfer resistance (R_ct) values raised and double layer capacitance (CPE_dc) values decreased with the increase of ZrO₂ vol. % to 7.139 vol % in Ni-3 sample and the higher amounts of nano-particle showed the opposite effect [27]. Therefore, there was good agreement between the results derived from potentiodynamic polarization and impedance spectroscopy analysis.

4. Conclusions

This study aimed to develop a co-deposition electroforming method to produce Ni–ZrO₂ composite parts, effectively enhancing the wear and corrosion resistance of the Ni-matrix. The potential of the economic and novel simple nickel-chloride electroforming bath for producing nickel composites was also investigated, and it was completely successful. The research analyzed the effect of direct current density and ZrO₂ nano-particle concentration on composited samples' morphological properties, corrosion, and wear resistance compared to pure nickel. In summary, the following conclusions were drawn.

• •The addition of more ZrO₂ powder into the bath and the increase in current density resulted in a higher volume percentage of ZrO₂ nano-particles in Ni-matrix. The increase in current density led to more uniformity of the nano-particle distribution and smaller nickel grains.
• •Regarding ZrO₂ volume percentage, it was observed that the more incorporated ZrO₂ in the matrix, the more ununiform surface, the more agglomerated particles, and the smaller nickel grains. The highest volume percentage of ZrO₂ size was detected in Samples Ni-4 by amounts of 13.65 vol % and 516.9 nm of nickel grain size.
• •Adding ZrO₂ particles to nickel composite foils increased wear resistance, reduced friction coefficient, and changed the wear mechanism to more abrasive behavior. The composite sample Ni-5 exhibited a 44 % lower friction coefficient than pure nickel.
• •The addition of ZrO₂ resulted in lower corrosion current density, a less negative corrosion potential, and increased corrosion resistance. This was confirmed by impedance spectroscopy analysis, which showed an increase in charge transfer resistance of the composited foils.

Data availability Statement

The data supporting this study's findings are available from the corresponding author upon reasonable request. The data are not publicly available due to restrictions, as the data were used under license for the current study and are not publicly available.

CRediT authorship contribution statement

Naghme Elahi Haghighi: Writing – original draft, Visualization, Validation, Software, Resources, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Mohammad Jafar Hadianfard: Writing – review & editing, Supervision, Project administration, Methodology, Conceptualization.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Naghme ElahiHaghighi reports equipment, drugs, or supplies was provided by Shiraz University. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.