Next Article in Journal
Interlayer Adhesion of Coating System in Analogue and Digital Printing Technologies Formed on Lightweight Honeycomb Furniture Panels
Previous Article in Journal
Enhancing Flame-Retardant Properties of Polyurethane Composites Using N-β-(Aminoethyl)-γ-aminopropyl Trimethoxysilane and Carbon Black Co-Modified Ammonium Polyphosphate
Previous Article in Special Issue
Microstructure and Wear Performance of TaC and Ta/TaC Coatings on 30CrNi2MoVA Steel
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Coatings
Volume 14
Issue 9
10.3390/coatings14091125
coatings-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Optimization of Black Nickel Coatings’ Electrodeposit onto Steel

by
Gabriel Santos
1,
Zohra Benzarti
1,2,*,
Diogo Cavaleiro
1,
Luís Figueiredo
3,
Sandra Carvalho
1 and
Susana Devesa
1,*
1
CEMMPRE, ARISE, Department of Mechanical Engineering, University of Coimbra, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal
2
Laboratory of Multifunctional Materials and Applications (LaMMA), Department of Physics, Faculty of Sciences of Sfax, University of Sfax, Soukra Road km 3.5, B.P. 1171, Sfax 3000, Tunisia
3
SRAMPORT Lda., Rua António Sérgio 15, 3025-041 Coimbra, Portugal
*
Authors to whom correspondence should be addressed.
Coatings 2024, 14(9), 1125; https://doi.org/10.3390/coatings14091125
Submission received: 2 August 2024 / Revised: 27 August 2024 / Accepted: 30 August 2024 / Published: 2 September 2024
(This article belongs to the Special Issue Oxidation, Wear, Corrosion Behaviors and Activated Bonding Properties of Coatings Deposited on Metals)
Browse Figures
Versions Notes

Abstract

:
Coatings can be created using various technologies and serve different roles, including protection, functionality, and decorative purposes. Among these technologies, electrodeposition has emerged as a low-cost, versatile, and straightforward process with remarkable scalability and manufacturability. Nickel, extensively studied in the context of electrodeposition, has many applications ranging from decorative to functional. The main objective of the present work is the electrodeposition of double-layer nickel coatings, consisting of a bright nickel pre-coating followed by a black nickel layer with enhanced properties, onto steel substrates. The influence of deposition parameters on colour, morphology, adhesion, roughness, and coefficient of friction was studied. The effects of cetyltrimethylammonium bromide (CTAB) and WS2 nanoparticles on the coatings’ properties and performance were also investigated. Additionally, the influence of the steel substrate’s pre-treatment, consisting of immersion in an HCl solution, prior to the electrodeposition, to etch the surface and activate it, was evaluated and optimized. The characterization of the pre-coating revealed a homogeneous surface with a medium superficial feature of 2.56 μm. Energy dispersive X-ray spectroscopy (EDS) results showed a high content of Ni, and X-ray diffraction (XRD) confirmed its crystallinity. In contrast, the black films’ characterization revealed their amorphous nature. The BN10 sample, which corresponds to a black nickel layer with a deposition time of 10 min, showed the best results for colour and roughness, presenting the lowest brightness (L*) value (closest to absolute black) and the most homogeneous roughness. EDS analysis confirmed the incorporation of WS2, but all samples with CTAB exhibited signs of corrosion and cracks, along with higher coefficient of friction (COF) values.

1. Introduction

Electrodeposition of nickel is part of a wide spectrum of electrodeposition branches, its first roots date back to the 19th century and spread over decades, with numerous obstacles and advancements, which made it thrive until nowadays. It is now relevant to do an extensive display of the most important achievements along the timeline, a brief representation of the most relevant advancements is shown in Figure 1.
The first steps were taken with work by Bottger, Bird, and Shore [1]. Unique contributions came to light, from patents on nickel nitrate solutions and former works on electrodeposition of nickel on platinum electrodes, to patents on effective formulations such as the Bottger one [1,2,3]. The Bottger formulation in 1843 comprised an aqueous solution of nickel and ammonium sulphate and was effectively recognised and used until the beginning of the next century, with some improvements along the way, marking this work as pioneering for nickel electrodeposition [1].
In this regard, Adams traced and patented the first improvements of these earlier formulations, and as the quality of the deposits increased, there was also an opportunity for business and consequently a boost of popularity regarding the wide use of nickel electrodeposition [4]. Objectively, Adams issued two main patents in 1869, the first one is related to a new formula with sulphite of nickel and sulphite or bisulphite of ammonia [5], and the other claimed two formulations with double sulphate of nickel and ammonia, and double chloride of nickel and ammonium, with a clear aim on the improvement of the bath’s performance [6]. It is important to note that the formulation claimed in the first patent is similar to Bottger’s, being the major improvement in regulating the pH of the bath and the mitigation of the damage provoked by nickel anodes contaminated with zinc, resulting in the quality enhancement of the deposits [1,5].
Alongside these avid innovations, Edward Weston also patented some of his work within the nickel electrodeposition scope in 1878. Objectively, Weston claims a relevant addition to the existing formulas, by introducing boric acid both in its free and combined state [7]. This work was quite important for the course of nickel electrodeposition since the addition of boric acid brought various improvements to this process. Hence, these advancements go from reducing the pitting and porosity of the deposits to boosting the velocity of the electrodeposition process, mainly because boric acid allows the use of more intense currents [7,8]. However, the advantages of using boric acid only bloomed years later when the patents ran out, given that there was apprehension for the violation of those. Consequently, competitors took advantage of this invention without paying Weston, so there is even documented use of acetic acid by the competition for similar outcomes [9].
Furthermore, there were some parallel works on anode performance and the influence of the bath on it. Thus, early work by Bancroft concluded that the use of chlorides influences the performance of the anode, more specifically that small amounts of it can reduce polarisation and boost the dissolution of the anode with 100% efficiency [4,8], this being ultimately important at the time, as a form of increasing the amount of nickel available in the bath. Therefore, there were even creations of baths that did not contain any nickel salts and relied only on the dissolution of the anode as a source of nickel, as Langbein described [10]. Additionally, the continuing development of nickel electrodeposition also encouraged scientists to go further into pH management and achieve better control of the quality and reproducibility of deposits. Brum’s work on the effect of boric acid and fluorites in nickel baths instigated the addition of boric acid as a pH buffer, which eventually turned on a light when it came to the addition of chemicals to control pH [4].
Moreover, one of the most relevant steps in the modern electrodeposition of nickel was made by Watts in 1916, with the contribution of an electrolyte made of nickel sulphate, nickel chloride, and boric acid, allowing higher speeds of deposition with the adjustment of optimum conditions [1]. In fact, this formula brought more advantages, such as higher efficiencies for the cathode and anode, more uniform and compact coatings with finer grains, and even energy savings [11], which all contributed to its wide use and dominance in the nickel industry until now, with some Watts-based formulas still being considered the easiest to use and maintain [1,12,13]. Nevertheless, some baths coexist and are counterparts of the Watts bath, such as the Sulfamate formulas used for electroforming [1,12] and the developing sulphate–gluconate solution [14].
However, the impetus for this technology was not only its functional aspect but also its decorative role, with many efforts to obtain shiny-looking coatings for a variety of decorative applications. Since Watts bath mainly leads to dull nickel films, all coatings had to be manually polished after electrodeposition, until a reflective finish was achieved, leading to the urging need for a bath that could create reflective and bright coatings without the need for extra operations [13,15]. As a result, researchers started to consider adding other components into the baths, being one of the most relevant works the inclusion of small amounts of naphthalene tri-sulfonic acid, naphthalene di-sulfonic acid and benzene by Schlotter in 1934 [16], and baths with coumarin, developed later by Du Rose [17]. Therefore, this led to the first formulas of bright and semi-bright nickel, respectively, opening the door to the inclusion of other kinds of brightening agents and additives. Nowadays, there is a long list of additives for bright nickel and many ways of categorizing it, but according to Schlesinger, the three main types are carriers, brighteners, and auxiliary brighteners [1]. It is still important to note that these brightening agents must be used in small concentrations, due to their impact on the internal stress and brittleness of the films, the reason why semi-bright nickel kept being relevant for functional applications, namely, when there is a need for more ductile coatings, being that semi-bright nickel is normally associated with lower use of additives [13,18]. Some even consider this class of nickel coatings a bridge between the bright nickel coatings and the later multilayer coatings, due to a better pairing and final result between the semi-bright nickel and the blooming bright chromium films at the time [18]. Ultimately, bright and semi-bright nickel have their own roles and are mostly obtained with the assistance of additives, being semi-bright nickel matte and less reflective than its bright counterpart, and more malleable [15].
On the other hand, and still in the decorative realm, some applications require coloured coatings beyond the white/greyscale offered by bright and semi-bright nickel, being the most frequent formulae for black films. Moreover, there is no actual disclosure about the invention of these black baths, but it is possible to find works and patents on the subject since the early 1950s. Particularly, in order to obtain black nickel coatings, these first baths all incorporate zinc chloride into the already-used formulas [19,20], which eventually developed into the use of standard baths like the Watts one for the same purpose, by adjusting deposition parameters, a practice still found nowadays [21]. Black nickel coatings are known for their weak corrosion and wear resistance and are generally thinner than their bright counterparts, which implies their use is heavily associated with pre-coatings of dull/bright/semi-bright nickel and it is scarcely on its own [1,22]. For this reason, most of the applications of these coatings are decorative and sometimes even partnered with a top film of lacquer or other organic finishes [22]. On the other hand, the first works on black nickel already report other kinds of applications, namely in the military industry due to these films’ low reflectivity and colour blending ability, and in optic and solar industries on account of its heat removal and light absorption efficiencies [19,22,23,24]. All this undoubtedly led to the niche usage of black nickel coating.
As technology developed, demanding applications came to light, and simple coatings such as bright and black nickel have struggled to perform. These developments did not just carry challenges, but also promising paths such as nanotechnology. Therefore, the benefits from the addition of suspended nanoparticles in the baths quickly bloomed, especially regarding the electrodeposition of a vast range of metals that some refer to as composite coating [25]. These advancements include the incorporation of numerous nanoparticles, such as Fe2O3, Al2O3, TiO2, SiO2, ZrO2, WC, WS2, and MoS2 [26]. The incorporation of these particles during the deposition of the coatings mainly aims at the improvement of the film’s properties. The morphology change of the films and refinement of grain size, provoked by these particles, lead to enhanced microhardness, wear and corrosion resistance and even the ability to become lubricated [25,27,28]. The ongoing development of nanotechnology is the main reason for the wide spectrum of available nanoparticles, so these composites may include nanoparticles of solid lubricants, hard oxides, nitrites, carbides and even particles of other metals [29]. As for tungsten disulfide, WS2, it can be classified as a solid lubricant, due to its specific layered structure that grants great lubrication properties. Additionally, these particles are inert and have high elasticity as a result of their morphology, which all labels them as promising, alongside other blooming and developing composite materials [30]. Ultimately, the addition of these particles also brings complexity to the electrodeposition process, with many challenges, from its concentration to the daring challenge of dispersing particles uniformly without great agglomeration, which is normally associated with the use of surfactants, ultrasound agitation and magnetic agitation [28].
Along those lines, is it now important to highlight another class of additives known as surfactants, not only as dispersing agents but also as a medium for coatings with enhanced surface properties. In this way, surfactants are mostly used as wetting agents, due to their chemical properties (specifically their hydrophobic and hydrophilic ends) that allow the reduction of surface tension between the liquid and the substrate, and ultimately prevent the interference of the hydrogen bubbles that form during the electrodeposition process [31]. These bubbles usually hold onto the surface of the pieces subject to coating and eventually lead to porosity and the formation of pits, this being the most frequent reason why surfactants are added to the baths [22]. On the other hand, the most relevant role of surfactants in this work happens to be the less frequent one, for instance, the way these agents improve the uniform distribution of solid and insoluble compounds, such as nanoparticles, and even prevent agglomeration and sedimentation of the same [31,32]. Thus, there are many wetting agents, and it is possible to classify them into different groups such as anionic, cationic, and non-ionic, being the surfactant subject to study in this work, cetyltrimethylammonium bromide (CTAB), classified as a cationic one. Nevertheless, as with any other surfactant, CTAB is a complex additive to work with, since it needs optimal concentrations to benefit from the above advantages, and when those concentrations are not met, it may compromise the electrodeposition process and the properties of the coatings [31,33].
Overall, the electrodeposition of nickel has come a long way, with many improvements and developments, which all led to its widespread use in the industry until today. Nonetheless, despite the progress made thus far, significant challenges remain to be addressed, and numerous barriers must be overcome. Additionally, new applications and opportunities continue to emerge.
All things considered, the main objective of this research is the development of chromium-free nickel-based films with enhanced tribological performance, that can compete with commonly used chromium coatings, both functional and aesthetically. The primary approach aims to avoid standard greyscale coatings and to achieve a black coating with enhanced mechanical properties. Therefore, the electrodeposition of black nickel poses an interesting trail to follow.
This study explores the influence of deposition parameters on the colour, morphology, adhesion, roughness, and coefficient of friction of dull and black nickel electrodeposited onto a steel substrate. Additionally, the effects of CTAB and WS2 nanoparticles on the black coating’s properties and performance were investigated. The pre-treatment of the steel substrate, which involved immersion in 25% V/V aqueous solution of HCl immediately before electrodeposition to etch and activate the surface, was also evaluated and optimized.

2. Materials and Methods

2.1. Electrodeposition

The electrodeposition was carried out in a polyethylene container, with an EA-PSI 9360-15 (Elektro-Automatik, Viersen, Germany) power supply and a 2831E digital multimeter (B&K Precision, Yorba Linda, CA, USA), installed as ammeter. The cathode was the substrate, a pretreated C35 steel plate with a deposition area of 3 cm2 and 1 mm thickness, and the anode was made of a rectangular piece of nickel (99.99%, Testbourne Ltd., Basingstoke, UK).
As displayed in Table 1, along with the deposition parameters, two different electrolytes, one for the deposition of the nickel pre-coating, and the other for the black nickel coating, were adopted. For the black nickel coatings, two different deposition times were evaluated, 5 and 10 min, giving rise to the reference samples, hereafter designated as BN5 and BN10, respectively.
Before the electrodeposition of the pre-coating, the substrate was chemically activated in a 25% V/V aqueous solution of HCl (Panreac, Barcelona, Spain).
Moreover, after establishing these parameters, the investigation followed the path of nanoparticle incorporation, aiming to study their adsorption and influence on the properties of the coatings. As stated before, tungsten disulfide nanoparticles have promising properties for composite coatings [27,30], so these were the selected ones for research.
The first challenge was the dispersion of said nanoparticles since magnetic agitation previously used was not enough. Some approaches were carried out, namely electrodeposition in an ultrasonic bath and the use of a surfactant. The use of an ultrasonic bath did not lead to promising results, with a total loss of adhesion. On the other hand, the use of CTAB proved to be effective in dispersing WS2 particles but also led to a partial loss of adhesion.
Being aware of the strict influence of CTAB on the stability of the bath, the concentration values used were conservative when compared to the ones found in the literature. Even with low concentrations, there was clear evidence of partial loss of adhesion.
Table 2 shows the content of CTAB and WS2 nanoparticles added to the black nickel electrolyte, resulting in the samples BN15A and BN15B. The deposition parameters were maintained, except the deposition time, which was increased to 15 min due to the lower deposition rate when these additives were included in the electrolyte.

2.2. Characterization Techniques

The 3D digital microscope RX-100 (Hirox, Tokyo, Japan) was used to examine the surface of the deposited coatings.
For the X-ray diffraction (XRD) analysis, the samples were investigated on a PANalytical X’Pert PRO diffractometer (PANalytical, Almelo, The Netherlands), with the following operation parameters: Cu Kα (λ = 1.54060 Å) radiation, 45 kV, 40 mA, and an incidence angle of 2°. Furthermore, the tests were carried out with a parallel beam geometry, with a range of 30° to 120° for parameter 2θ, a step size of 0.025°, and an exposure time of 1 s per step.
The surface and cross-section of the samples were characterized by scanning electron microscopy (SEM) on a SU3800 microscope from Hitachi (Tokyo, Japan) and a Zeiss Merlin microscope (Zeiss, Oberkochen, Germany), respectively, operating in secondary electrons mode. The analysis of the chemical composition of the films was made by energy dispersive X-ray spectroscopy (EDS), on a Bruker Nano (Berlin, Germany) equipment, with an accelerating voltage of 10 kV.
The colour of the coatings was measured on a Gretagmacbeth ColorEye® XTH spectrophotometer (Grand Rapids, MI, USA). This equipment measures the colour coordinates in the CIE-L*a*b* colour space, which is the most commonly used approach for human colour perception.
The surface topography was examined using atomic force microscopy (AFM) in tapping mode, using SiN tip with tip radius below 8 nm. AFM micrographs were taken over 10 × 10 μm2 and 2D and 3D profiles of each sample were generated after leveling and applying polynomial background filters. The average roughness (Sa) was obtained through the roughness subroutine of the AFM Innova (Veeco, Plainview, NY, USA) apparatus from four independent measurements.
In order to study friction and wear of the coatings, a tribological investigation was conducted. The equipment used for the purpose was a reciprocating ball-on-slab tribometer (SRV™ 2, Optimol Instruments, Munich, Germany), with an upper counter body made out of a 100Cr6 bearing steel ball with 10 mm of diameter, chrome plated. To carry out the tests, the following settings were used: 2 N load, 20 cycles, an oscillating frequency of 1 Hz, and a 4 mm stroke.

3. Results

3.1. Chemical Activation and Pre-Coating

The substrate surface properties are utterly important for the successful electrodeposition of coatings, so it is relevant to present a brief highlight of its composition and certain characterisation. Therefore, the substrate was a C35 carbon steel plate, a medium carbon steel that is frequently used in the marine, railway, and structural industries, due to its mechanical properties such as improved tensile and yield strength [34]. The composition of this carbon steel, given by ASTM A105 [35], shows an Fe content in the range of 98.25%–99.30%.
The XRD diffractogram for the substrate is presented in Figure 2. The stick pattern for metallic iron is also included (ICDD 04-007-9753 [36]), showing that all the substrate peaks correspond to cubic Fe peaks, which is well aligned with the high content of Fe.
The morphology of the steel substrate was also analysed by SEM, at two different magnification settings, ×500 and ×2 k, as shown in Figure 3. The surface is not smooth, with the presence of numerous imperfections, possible scratches and metallurgical defects [37], due to the fact that the steel was characterised as received. Some of these features are identified in Figure 3b.
Pre-coating is a crucial step in order to improve the adhesion of the subsequent black coating. Along those lines, the lack of adhesion was one of the most challenging problems when depositing both bright/dull and black nickel coatings.
Being important to enhance the adhesion of the pre-coating to the substrate, and making sure that the black coating has optimum conditions to be deposited, there was an extensive investigation on the chemical activation of the substrate, namely the influence of immersing the substrate in different chemical baths, specifically acetone, ethanol, sodium hydroxide, and hydrochloric acid [38,39,40].
The most promising results came from an aqueous solution of HCl (25% V/V, Panreac). The immersion in HCl solutions removes any organic residues and oxide layers that may be present on the steel surface. This promotes the chemical activation of the surface and consequently enhances the adhesion of the pre-coating to the substrate [1]. Therefore, Figure 4 displays the SEM micrographs of the substrate after the HCl activation, showing different surface morphology, with porosity and possible higher roughness, which is also part of the adhesion enhancement mechanism of HCl [1,41].
Various immersion times of the steel substrate in the 25% V/V aqueous HCl solution were studied, all leading to clean, good adhesion, and some influence on the surface appearance of the deposited pre-coatings. Higher times of immersion of the substrate lead to smoother-looking surfaces, with homogenous, uniform and compact films of bright/dull nickel.
Figure 5 shows the optical images of two pre-coatings, electrodeposited in the same conditions, on the same base substrate, but with different immersion times on HCl. So, the optimum time for chemical activation was set to 20 min, with a subsequent rinse with deionized water.
The electrolyte composition corresponding to the pre-coating, previously presented in Table 1, differs from the conventional Watts bath and was achieved through an extensive study, since not all baths described in the literature for producing dull or bright nickel coatings are suitable for creating films that can serve as a pre-coating for a black nickel layer, with the adhesion of the black layer being the primary challenge. Without the appropriate pre-coating, the deposited black nickel layer is partially or completely removed during the standard cleaning procedure with deionized water and a soft tissue. This challenge was overcome with a composition that does not offer significant environmental advantages compared to Watts-based baths but is much more cost-effective, an advantage that cannot be disregarded when the scale-up is considered.
The deposition parameters established for the pre-coating, also displayed in Table 1, were based on the 3D digital microscope observation, which confirmed a homogenous and pinhole-free surface.
The cross-section of the pre-coating was examined by SEM. Figure 6a displays the polished profile of the film, as well as a fractured area, which is presented with higher magnification in Figure 6b. It can be observed that the nickel film presents a columnar structure, which is well aligned with the literature since the grain structure of dull/semi-bright nickel deposits is usually columnar compared with the banded (laminar) structure of bright nickel [22].
This analysis also enabled the measurement of the film thickness, with the corresponding SD, which was (2.8 ± 0.1) μm.
Additionally, the thickness value allows for the evaluation of the deposition rate of the pre-coating, which is estimated to be ≈ 0.6 μm/min.
The XRD diffractogram of the pre-coating is presented in Figure 7. The stick pattern for metallic nickel (ICDD 04-010-6148 [42]) is also shown for comparison. Therefore, all the peaks can be assigned to cubic nickel, which suggests that the coating’s composition might be mostly crystalline nickel.
The generally accepted mechanism for metallic nickel electrodeposition involves two sequential one-electron charge transfers, and the participation of an anion, X−, with the formation of an adsorbed complex. This mechanism can be described by the following equations [43,44,45,46]:
Ni2+ + X− → Ni X+
Ni X+ + e− → Ni Xads
Ni Xads + e− → Ni + X−
Since the anions present in the electrochemical bath are OH− and Cl−, previous studies show that the anion X− is usually Cl−.
Figure 8 provides an insight into the morphology and superficial features of the electrodeposited nickel pre-coating, at three different magnification settings: 500×, 2000× and 5000×. This film shows a homogeneous and compact surface. The compactness is confirmed by the low porosity, and the absence of pinholes is verified. Additionally, the surface appears to be formed by superficial features with characteristic circular shapes, as in a nodular type of morphology, and delimited by clear and well-defined boundaries. Using ImageJ software (version 1.53m), four measurements were conducted for each surface feature, including the long and short axes. The average size of each surface feature was estimated based on these measurements. Therefore, considering 113 features, a histogram was built and is shown in Figure 9. This feature size ranges from 1.50 to 5.27 μm and the multiple measurements allowed us to estimate a medium size of 2.56 mm.
Furthermore, the EDS analysis allowed a better understanding of the coating’s composition. Thus, Table 3 shows that the pre-coating is predominantly made of nickel, with a low presence of oxygen, which is consistent with the XRD analysis.

3.2. Black Nickel Coatings

The black nickel coating was the focus of this work, with its colour, evenness, and adhesion being the primary targets. As shown in Table 1, the electrolyte formulation used for the black coating is similar to the one used for the pre-coating, except for the exclusion of boric acid.
Among the parameters considered, and also displayed in the same table, the time of deposition and current density were the most extensively explored. This is because agitation was set to avoid vortex formation; pH was monitored, but its control was avoided to keep the electrolyte as simple as possible; room temperature was used to save energy and costs when scaling up; and electrodes were fixed in position and distance, with no further study conducted since electrode positioning has minimal impact in an industrial setting.
Regarding the current density, low current densities (0.67–2.00 mA/cm2) led to flawed coatings, and higher current densities (>3.30 mA/cm2) did not promote the deposition of black films. Consequently, its optimal value was dictated by the sample with the best adhesion, colour, uniformity and absence of imperfections.
The investigation into the deposition time revealed that durations below 5 min were insufficient to coat the entire surface of the plate, while times exceeding 10 min resulted in decreased colour and uniformity quality. Therefore, deposition times of 5 to 10 min were established.
After establishing the most promising parameters, the investigation followed the path of nanoparticle incorporation, aiming to study their adsorption and influence on the properties of the coatings. As stated before, tungsten disulfide nanoparticles have promising properties for composite coatings [27,30], so these were the selected ones for research.
The first challenge was the dispersion of said nanoparticles, since magnetic agitation previously used was not enough. Some approaches were carried out, namely electrodeposition in an ultrasonic bath and the use of a surfactant. The use of an ultrasonic bath did not lead to promising results, with a total loss of adhesion. On the other hand, the use of CTAB proved to be effective in dispersing WS2 particles but led to a partial loss of adhesion.
Being aware of the strict influence of CTAB on the stability of the bath, the concentration values used were conservative when compared to the ones found in the literature. Even with low concentrations, there was clear evidence of partial loss of adhesion, which lead to a parallel study about the influence of CTAB, without nanoparticles in the bath. Therefore, it was possible to conclude that CTAB on its own lead to partial or total loss of adhesion, regardless of its concentration, being higher concentrations associated to a total loss. Considering the unfavorable conditions, the stablished deposition time had to be adjusted to 15 min.
Consequently, the most promising samples were selected for further characterization to better understand the influence of CTAB on the black nickel coatings and the potential incorporation of WS2 nanoparticles. The base electrolyte was the same as that used for previous black nickel samples, but with the addition of different concentrations of CTAB and WS2, as previously shown in Table 2, resulting in samples BN15A and BN15B.
The cross-section of the black coatings was examined by SEM, as shown in Figure 10. The measured thicknesses of samples BN5 and BN10 were (0.5 ± 0.1) μm and (1.1 ± 0.1) μm, respectively. Considering these values, the deposition rate of the black nickel can be estimated to be approximately 0.1 μm/min. For the samples with additives, BN15A and BN15B, the measured thickness was (1.7 ± 0.2) μm and (1.4 ± 0.1) μm, respectively, which also implies a deposition rate of ≈0.1 μm/min. These results allow us to infer that, at the adopted concentrations, the WS2 nanoparticles and the CTAB have a minor impact on the deposition rate of these black films.
Differing from the dull metallic nickel deposits, it is difficult to predict the chemical nature of these coatings. Nevertheless, black nickel electrodeposition involves multiple reduction processes along with oxidative processes, resulting in a complex composition that can contain α-Ni(OH)2, NiOOH, Ni2O3, NiO, water and metallic Ni, depending on different factors, such as surface pH, reagent concentrations and temperature [44,47].
Therefore, the XRD diffractograms of the black coatings are shown in Figure 11, along with the previously analyzed diffractogram of the pre-coating (PC). All the peaks in the black films correspond to the pre-coating’s peaks, confirming the amorphous nature of the black nickel films and showing consistency with the low thickness measured.
Morphological characterisation of the black nickel coatings was carried out with SEM, with the samples BN5, BN10, BN15A and BN15B being analyised with two different magnification settings: 500× and 5k×.
As shown in Figure 12, samples BN5 and BN10, both have similar morphology, a compact and reasonably homogeneous surface, with clear defects, again similar to the ones found before at the pre-coating surface. Considering that the coating adjusts to the morphology of the pre-coating as it deposits, this might indicate the thin nature of the black coatings [48]. At higher magnification, it is possible to confirm the homogenous and compact nature of the surface, as there are no visible pinholes or signs of high porosity. Additionally, there are punctual heterogeneities, some of them highlighted in Figure 12a,c, that may be either coating discontinuities, wider feature boundaries or even thickness irregularities, that tend to decrease with the increase in the deposition time.
As for samples BN15A and BN15B, Figure 13, there is a homogenous surface morphology even though there are signs of low compacity and indication of cracks. The low compacity is confirmed at further magnifications since the surface is extensively cracked. There are some possible reasons for the cracked surface, namely the loss of adhesion to the pre-coating. In fact, CTAB may affect negatively the mechanical properties of the coating, specifically enabling crack phenomena [49]. Additionally, it is possible to observe contrasting protrusions of various sizes, that appear to be on top of the coating’s surface, which are suspected as being related to corrosion.
Additionally, EDS analysis provided information about the composition of the coatings, specifically the incorporation of WS2, and confirmed the corrosion observations.
The EDS results revealed that all samples have similar Ni:O ratios being the specific values for BN5 and BN10 presented in Table 4. The proportion between Ni and O is neither 1:1 for NiO, nor 2:3 for Ni2O3, probably due to the low thickness of the black coatings, which possibly led to the detection of the pre-coating’s nickel. Although it is not possible to draw conclusions about specific compounds, previous studies have shown that the electrodeposition of black nickel from a nickel chloride and sodium chloride solution in a slightly acidic medium promotes the sequential formation of NiO and Ni2O3. NiO is the first oxide to form and is predominantly present at greater depths, while Ni2O3 can be found at the surface of the film [50,51].
An additional SEM image of the BN15A surface is shown in Figure 14, along with EDS spectra of three different regions. The EDS spectra revealed that the contrasting protrusions have a strong signal for iron, Figure 14c, which suggests the formation of an iron oxide. The same results were obtained for sample BN15B.
Furthermore, there are some signs of WS2 incorporation, since there are peaks of W and S in the spectrum, shown in Figure 14d, and even with the possibility of the formation of agglomerates since they are present in some protrusions, as can be seen in Figure 14b. It is still possible to see the presence of chlorine, implying its incorporation during electrochemical deposition.
For the AFM analysis, only the uncracked samples, BN5 and BN10, were investigated. The average roughness (Sa) was obtained through the roughness subroutine of the AFM apparatus from six independent measurements. The results are shown as roughness values summarized in Table 5 and as 2D and 3D images of the surface in Figure 15.
Hence, both coatings show considerable roughness, which is clearly visible in the 2D and 3D images. The standard deviation values indicate the evolution of the roughness along the surface. Therefore, it is clear that the time of deposition reduces roughness and heterogeneity.

3.3. Optical Properties

Evaluating the appearance of samples by observing them with the naked eye or even with an optical microscope may be misleading, as different light conditions lead to different perceptions of colour and even brightness. It is then important to characterise them objectively, being reflectivity and CIE L*a*b* colour coordinates the right tool for it. Moreover, even though the main focus of the present work is the appearance of the black nickel coatings, it is still relevant to characterise the dull nickel coating and understand if it poses any competition to chromium coatings when it comes to aesthetics.
The CIE L*a*b* colour diagram of the samples and its brightness are represented on Figure 16 and Table 6, respectively.
As for a* and b*, all samples fall on the red and yellow hue quadrant, except BN15B, which falls on the red and blue one. PC has the strongest yellow hue, and the pair BN15A/BN15B has the most neutral hue. Therefore, a higher time of deposition may have led to a slight increase in both the yellow and the red hue, at the same time that the introduction of the WS2 nanoparticles and the CTAB originated more neutral hue coatings.
Regarding the brightness (L*) values, the first remark is about the PC, which has an expected higher value that can be considered within the range of L* values for chromium coatings [52,53]. Sample BN15A has the highest L* value among the black coatings, and BN10 has the lowest one, indicating that BN10 is the closest to absolute black (0).

3.4. Tribological Properties

With regard to the tribological study, a wear test was carried out. The morphology of wear tracks for samples BN5 and BN10 is shown in Figure 17, and the values for the coefficients of friction (COF) for all samples are plotted in Figure 18. The SEM micrographs of the wear tracks were not investigated for BN15A and BN15B due to their previously confirmed corrosion problems, cracked surfaces, and higher COF values. Specific wear rates were not possible to measure due to the thin nature of the black coatings, in conjunction with its considerable roughness, which had the same order of magnitude as the track depth.
Therefore, the SEM images reveal similar plastic deformation on both coatings, with a fish-like appearance, which might be explained by the higher hardness of the ball. However, BN5 appears to have a less uniform track surface, which can be related to a thinner deposit, and there are signs of delamination wear [54]. EDS analysis did not detect any material from the ball, which may underline the hardness theory. It also confirmed that the composition of the tracks is similar to that of the coating, indicating that the wear did not reach the pre-coating layer.
As for the COF values, it is possible to note that BN15A and BN15B have particularly high jumps in the first cycles of the test. This is justified by the initial contact between the ball and the imperfections that may interfere in both surfaces, which eventually stabilize and translate as steadier COF values [55,56]. This explanation agrees with the heterogeneity of roughness revealed during the AFM analysis. The curve of BN10 has overall lower values, which may suggest the best COF. It is also the smoother one, regarding stabilisation, which is in accordance both with its lower roughness heterogeneity, studied previously, and with its smooth track surface.
The reference values for mild steel (COF ∈ [0.5;0.6]) and pure nickel (COF ∈ [0.55;0.8]) allow us to confirm that the wear did not reach the substrate [57]. It is also observable that BN5 and BN10 might have slightly better COF values than mild steel. The promising results for the pre-coating, when compared with pure nickel, might be justified by the fact that different parameters and bath compositions lead to different results. In fact, these results could translate as an optimized COF value for the pre-coating. In addition, according to Mahidashti [58], the use of CTAB and WS2 promotes the lowering of COF due to the lubricating nature of WS2 and CTAB’s influence on surface properties and WS2 incorporation. However, samples BN15A and BN15B did not present this enhancement, which may emphasise, once again, the disruptive behaviour of CTAB on these coatings.

4. Conclusions

The main objective of this investigation was the development of black coatings with enhanced properties using electrodeposition. Consequently, an emphasis was placed on the influence of deposition parameters on the appearance, colour quality, composition, adhesion, and overall surface properties of the coatings. The study also examined the effects of CTAB and WS2 on the coating properties.
The influence of substrate pre-treatment on coating adhesion was demonstrated, and the conditions for this chemical activation were optimised.
Regarding the pre-coating, SEM analysis showed a homogeneous surface with an average feature size of 2.56 μm. EDS and XRD investigations confirmed the high content of Ni and its crystallinity, respectively. The pre-coating proved essential for the adhesion of the black coating, which otherwise showed poor adhesion to the substrate. Additionally, its L* value is similar to reference values for chromium coatings.
For the black coatings, XRD analysis confirmed the amorphous nature of the black nickel films. SEM showed the homogeneous and compact nature of the reference coatings’ surfaces, with no visible pinholes or cracks. However, the samples with additives exhibited signs of corrosion, cracked surfaces, and adhesion problems. Their colour, brightness, and COF values were also less promising compared to the reference samples.
The reference sample BN10 had the lowest L* value and is, therefore, the closest to absolute black. This sample also had the least heterogeneous and smoothest surface, as well as a slightly lower COF.

Author Contributions

Conceptualization, G.S., S.C. and S.D.; methodology, G.S. and S.D.; validation, G.S. and S.D.; formal analysis, G.S. and S.D.; investigation, G.S., D.C. and Z.B.; resources, L.F. and S.C.; data curation, G.S. and S.D.; writing—original draft preparation, G.S.; writing—review and editing, D.C., L.F., Z.B., S.D. and S.C; visualization, G.S. and S.D.; supervision, S.D. and S.C.; project administration, L.F. and S.C.; funding acquisition, S.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research is sponsored by national funds through FCT—Fundação para a Ciência e Tecnologia, under projects UIDB/00285/2020 and LA/P/0112/2020. Also, this research is financed by PRR—Recovery and Resilience Plan and by the Next Generation EU Funds, following NOTICE N.º 02/C05-i01/2022, Component 5—Capitalization and Business Innovation—Mobilizing Agendas for Business Innovation under the AM2R project “Mobilizing Agenda for business innovation in the Two Wheels sector” (reference: 7253).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors upon request.

Conflicts of Interest

Author Luís Figueiredo was employed by SRAMPORT Lda. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Schlesinger, M.; Paunovic, M. Modern Electroplating, 5th ed.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2010. [Google Scholar] [CrossRef]
  2. Boettger, R. Ueber eine einfaclce Methode, Baumwollfaden in Leinengeioeben nachzuweisen. J. Prakt. Chem. 1843, 30, 257–275. [Google Scholar] [CrossRef]
  3. Bird, G.V. Observations on the electro-chemical influence of long-continued electric currents of low tension. Philos. Trans. R. Soc. Lond. 1837, 127, 37–45. [Google Scholar] [CrossRef]
  4. Dubpernell, G. The Story of Nickel Plating—Part I. Plat. Surf. Finish. 2006, 93, 34–43. [Google Scholar]
  5. Adams, I. Improved Mode of Electroplating with Nickel. US90332A, 25 May 1869. [Google Scholar]
  6. Adams, I. Improvement in the Electro-Deposition of Nickel. US93157, 3 August 1869. [Google Scholar]
  7. Weston, E. Improvement in Nickel-Plating. US211071, 17 December 1878. [Google Scholar]
  8. Thompson, J.G. Nickel and Its Alloys l; National Bureau of Standards Circular 592; United States Department of Commerce: Washington, DC, USA, 1958. [Google Scholar]
  9. Woodbury, D.O. A Measure for Greatness: A Short Biography of Edward Weston, 1st ed.; McGraw-Hill: New York, NY, USA, 1949. [Google Scholar]
  10. Langbein, G. A Complete Treatise on the Electro-Deposition of Metals, 3rd ed.; Henry Carey Baird & Co.: Philadelphia, PA, USA, 1898. [Google Scholar]
  11. Wesley, W.A.; Carey, J.W. The electrodeposition of nickel from nickel chloride solutions. Trans. Electrochem. Soc. 1939, 75, 209. [Google Scholar] [CrossRef]
  12. Azem, N.F.A.; Birlik, I. Influence of Bath Composition on the Structure and Properties of Nickel Coatings Produced by Electrodeposition Technique. J. Sci. Eng. 2018, 20, 689–697. [Google Scholar] [CrossRef]
  13. Hanson, D. Electroplating, 1st ed.; The Crowood Press Ltd.: Marlborough, UK, 2023. [Google Scholar]
  14. Rudnik, E.; Wojnicki, M.; Włoch, G. Effect of gluconate addition on the electrodeposition of nickel from acidic baths. Surf. Coat. Technol. 2012, 207, 375–388. [Google Scholar] [CrossRef]
  15. Nebiolo, W.P. The History of Electroplating and A Historical Review of the Evolution of NASF. NASF Surf. Technol. White Pap. 2022, 86, 11. [Google Scholar]
  16. Schlotter, M. Formation of Dense, Highly Lustrous and Impervious Deposits of Nickel. US1972693, 10 November 1932. [Google Scholar]
  17. Rose, A.H.D. Bright Nickel Plating. US2635076, 29 January 1947. [Google Scholar]
  18. Sellers, W.W. A Retrospective View of Nickel Plating. Surf. Technol. White Pap. 2013, 100, 14–23. [Google Scholar]
  19. Wesley, W.A.; Knapp, B.B. Black Nickel Plating. US2844530, 15 February 1957. [Google Scholar]
  20. Singler, J.C. Metal Blackening Composition and Method. US2679475, 21 January 1952. [Google Scholar]
  21. Zhou, J.; Zhao, G.; Li, J.; Chen, J.; Zhang, S.; Wang, J.; Walsh, F.C.; Wang, S.; Xue, Y. Electroplating of Non-Fluorinated Superhydrophobic Ni/WC/WS2 Composite Coatings with High Abrasive Resistance. Appl. Surf. Sci. 2019, 487, 1329–1340. [Google Scholar] [CrossRef]
  22. Nickel Institute. Nickel Plating Handbook—Knowledge for a Brighter Future; Nickel Institute: Toronto, ON, Canada, 2022. [Google Scholar]
  23. Gamburg, Y.D.; Zangari, G. Theory and Practice of Metal Electrodeposition; Springer: New York, NY, USA, 2011. [Google Scholar]
  24. Koltun, M.; Gukhman, G.; Gavrilina, A. Stable Selective Coating “Black Nickel” for Solar Collector Surfaces. Sol. Energy Mater. Sol. Cells 1994, 33, 41–44. [Google Scholar] [CrossRef]
  25. Aruna, S.; Bindu, C.; Selvi, V.E.; Grips, V.W.; Rajam, K. Synthesis and Properties of Electrodeposited Ni/Ceria Nanocomposite Coatings. Surf. Coat. Technol. 2006, 200, 6871–6880. [Google Scholar] [CrossRef]
  26. Wang, M.; Xue, Z.; Yan, S.; He, J.; Shao, Q.; Ge, W.; Lu, B. Pulse Electrodeposited Super-Hydrophobic Ni-Co/WS2 Nanocomposite Coatings with Enhanced Corrosion-Resistance. Coatings 2022, 12, 1897. [Google Scholar] [CrossRef]
  27. Low, C.T.J.; Wills, R.G.A.; Walsh, F.C. Walsh. Electrodeposition of Composite Coatings Containing Nanoparticles in a Metal Deposit. Surf. Coat. Technol. 2006, 201, 371–383. [Google Scholar] [CrossRef]
  28. Tudela, I.; Zhang, Y.; Pal, M.; Kerr, I.; Cobley, A.J. Ultrasound-Assisted Electrodeposition of Thin Nickel-Based Composite Coatings with Lubricant Particles. Surf. Coat. Technol. 2015, 276, 89–105. [Google Scholar] [CrossRef]
  29. Low, C.; Bello, J.; Wharton, J.; Wood, R.; Stokes, K.; Walsh, F. Electrodeposition and Tribological Characterisation of Nickel Nanocomposite Coatings Reinforced with Nanotubular Titanates. Surf. Coat. Technol. 2010, 205, 1856–1863. [Google Scholar] [CrossRef]
  30. García-Lecina, E.; García-Urrutia, I.; Díez, J.; Fornell, J.; Pellicer, E.; Sort, J. Codeposition of Inorganic Fullerene-like WS2 Nanoparticles in an Electrodeposited Nickel Matrix under the Influence of Ultrasonic Agitation. Electrochi. Acta 2013, 114, 859–867. [Google Scholar] [CrossRef]
  31. Kanani, N. Electroplating—Basic Principles, Processes and Practice, 1st ed.; Elsevier: Amsterdam, The Netherlands, 2004. [Google Scholar]
  32. Walsh, F.C.; Low, C.T.J.; Bello, J.O. Influence of Surfactants on Electrodeposition of a Ni-Nanoparticulate SiC Composite Coating. Trans. Inst. Met. Finish. 2015, 93, 147–156. [Google Scholar] [CrossRef]
  33. Zhang, H.; Zhang, N.; Fang, F. Synergistic Effect of Surfactant and Saccharin on Dispersion and Crystal Refinement for Electrodeposition of Nanocrystalline Nickel/Graphene Oxide Composite. Surf. Coat. Technol. 2020, 402, 126292. [Google Scholar] [CrossRef]
  34. Kumar, M.; Rana, M.; Kannan, M. Some Studies on the Performance of Activated-TIG Welding in Steel Weldments. Int. J. Mech. Prod. Eng. Res. Dev. (IJMPERD) 2019, 5–10. [Google Scholar]
  35. ASTM International. Standard Specification for Carbon Steel Forgings for Piping Applications 1; ASTM International: West Conshohocken, PA, USA, 2010. [Google Scholar]
  36. Ohba, S.; Saito, Y.; Noda, Y. A Measurement of Charge Aspherieity in Iron Metal. Acta Cryst. 1982, 38, 725–729. [Google Scholar] [CrossRef]
  37. Papaefthymiou, S.; Tzevelekou, T.; Antonopoulos, A.; Gypakis, A. Typical Defects in Plate and Long Steel Products. Int. J. Struct. Integr. 2016, 7, 645–655. [Google Scholar] [CrossRef]
  38. Wang, Y.; Zhang, G.; He, Z.; Chen, J.; Gao, W.; Cao, P. Superhydrophobic Ni Nanocone Surface Prepared by Electrodeposition and Its Overall Performance. Surf. Coat. Technol. 2023, 464, 129548. [Google Scholar] [CrossRef]
  39. Zhang, F.; Yao, Z.; Moliar, O.; Tao, X.; Yang, C. Nanocrystalline Ni Coating Prepared by a Novel Electrodeposition. J. Alloys Compd. 2020, 830, 153785. [Google Scholar] [CrossRef]
  40. Wahab, H.A.; Noordin, M.Y.; Izman, S.; Kurniawan, D. Quantitative Analysis of Electroplated Nickel Coating on Hard Metal. Sci. World J. 2013, 2013, 631936. [Google Scholar] [CrossRef]
  41. Liu, R.; Yuan, Y.; Wang, H.; Guo, X. Adhesion Performance of Electrodeposited Ni Films with Different Treating Methods. Coatings 2018, 8, 201. [Google Scholar] [CrossRef]
  42. Takeshita, H.T.; Oishi, T.; Kuriyama, N. Disproportionation of CaNi3 Hydride: Formation of New Hydride: CaNiH3. J. Alloys Compd. 2002, 333, 266–273. [Google Scholar] [CrossRef]
  43. Okonkwo, B.O.; Jeong, C.; Jang, C. Advances on Cr and Ni Electrodeposition for Industrial Applications—A Review. Coatings 2022, 12, 1555. [Google Scholar] [CrossRef]
  44. Estrella-Gutiérrez, M.; Lizama-Tzec, F.; Arés-Muzio, O.; Oskam, G. Influence of a Metallic Nickel Interlayer on the Performance of Solar Absorber Coatings Based on Black Nickel Electrodeposited onto Copper. Electrochim. Acta 2016, 213, 460–468. [Google Scholar] [CrossRef]
  45. Wang, P.; Cheng, Y.-L.; Zhang, Z. A Study on the Electrocodeposition Processes and Properties of Ni-SiC Nanocomposite Coatings. J. Coat. Technol. Res. 2011, 8, 409–417. [Google Scholar] [CrossRef]
  46. Oriňáková, R.; Turoňová, A.; Kladeková, D.; Gálová, M.; Smith, R.M. Recent Developments in the Electrodeposition of Nickel and Some Nickel-Based Alloys. J. Appl. Electrochem. 2006, 36, 957–972. [Google Scholar] [CrossRef]
  47. Lizama-Tzec, F.; Herrera-Zamora, D.; Arés-Muzio, O.; Gómez-Espinoza, V.; Santos-González, I.; Cetina-Dorantes, M.; Vega-Poot, A.; García-Valladares, O.; Oskam, G. Electrodeposition of Selective Coatings Based on Black Nickel for Flat-Plate Solar Water Heaters. Sol. Energy 2019, 194, 302–310. [Google Scholar] [CrossRef]
  48. Mennucci, M.M.; Montes, R.; Bastos, A.C.; Monteiro, A.; Oliveira, P.; Tedim, J.; Ferreira, M.G.S. Nanostructured Black Nickel Coating as Replacement for Black Cr(VI) Finish. Appl. Sci. 2021, 11, 3924. [Google Scholar] [CrossRef]
  49. Guo, C.; Zuo, Y.; Zhao, X.; Zhao, J.; Xiong, J. Effects of Surfactants on Electrodeposition of Nickel-Carbon Nanotubes Composite Coatings. Surf. Coat. Technol. 2008, 202, 3385–3390. [Google Scholar] [CrossRef]
  50. Duta, A.; Bogatu, C.; Chitanu, G.C.; Pelin, M.I. Electrochemical Deposition of Ni-based Thin Film Cermets Using Polymeric Additives. Phys. Status Solidi C 2008, 5, 3530–3534. [Google Scholar] [CrossRef]
  51. Wäckelgård, E. Characterization of Black Nickel Solar Absorber Coatings Electroplated in a Nickel Chlorine Aqueous Solution. Sol. Energy Mater. Sol. Cells 1998, 56, 35–44. [Google Scholar] [CrossRef]
  52. Leimbach, M.; Tschaar, C.; Zapf, D.; Kurniawan, M.; Schmidt, U.; Bund, A. Relation between Color and Surface Morphology of Electrodeposited Chromium for Decorative Applications. J. Electrochem. Soc. 2019, 166, 205–211. [Google Scholar] [CrossRef]
  53. Ponte, F.; Sharma, P.; Figueiredo, N.M.; Ferreira, J.; Carvalho, S. Decorative Chromium Coatings on Polycarbonate Substrate for the Automotive Industry. Materials 2023, 16, 2315. [Google Scholar] [CrossRef]
  54. Li, X.; Shen, Q.; Zhang, Y.; Wang, L.; Nie, C. Wear Behavior of Electrodeposited Nickel/Graphene Composite Coating. Diam. Relat. Mater. 2021, 119, 108589. [Google Scholar] [CrossRef]
  55. Castro, J.D.; Ans, M.; Cavaleiro, D.; Carvalho, S. Tribological and Mechanical Properties of ZrxNy Films Obtained by HiPIMS in DOMS Mode. Tribol. Int. 2023, 189, 108960. [Google Scholar] [CrossRef]
  56. Cardinal, M.; Castro, P.; Baxi, J.; Liang, H.; Williams, F. Characterization and Frictional Behavior of Nanostructured Ni-W-MoS2 Composite Coatings. Surf. Coat. Technol. 2009, 204, 85–90. [Google Scholar] [CrossRef]
  57. Surender, M.; Basu, B.; Balasubramaniam, R. Wear Characterization of Electrodeposited Ni-WC Composite Coatings. Tribol. Int. 2004, 37, 743–749. [Google Scholar] [CrossRef]
  58. Mahidashti, Z.; Aliofkhazraei, M.; Lotfi, N. Review of Nickel-Based Electrodeposited Tribo-Coatings. Trans. Indian Inst. Met. 2018, 71, 257–295. [Google Scholar] [CrossRef]
Coatings 14 01125 g001
Figure 1. Schematic of the most relevant achievements for nickel electrodeposition.
Figure 1. Schematic of the most relevant achievements for nickel electrodeposition.
Coatings 14 01125 g001
Coatings 14 01125 g002
Figure 2. (a) XRD diffractogram of the substrate and (b) stick pattern for iron (ICDD 04-007-9753).
Figure 2. (a) XRD diffractogram of the substrate and (b) stick pattern for iron (ICDD 04-007-9753).
Coatings 14 01125 g002
Coatings 14 01125 g003
Figure 3. Surface SEM micrographs of the substrate, with a magnification of (a) 500× and (b) 2000×.
Figure 3. Surface SEM micrographs of the substrate, with a magnification of (a) 500× and (b) 2000×.
Coatings 14 01125 g003
Coatings 14 01125 g004
Figure 4. Surface SEM micrographs of the substrate after 20 min of HCl bath, with a magnification of (a) 500× and (b) 2000×.
Figure 4. Surface SEM micrographs of the substrate after 20 min of HCl bath, with a magnification of (a) 500× and (b) 2000×.
Coatings 14 01125 g004
Coatings 14 01125 g005
Figure 5. Surface optical image of the pre-coating deposited in a substrate subject to an HCl activation for (a) 20 min and (b) 5 min.
Figure 5. Surface optical image of the pre-coating deposited in a substrate subject to an HCl activation for (a) 20 min and (b) 5 min.
Coatings 14 01125 g005
Coatings 14 01125 g006
Figure 6. Cross-section SEM image of the nickel pre-coating, with a magnification of (a) 1.25 kx and (b) 4.00 kx.
Figure 6. Cross-section SEM image of the nickel pre-coating, with a magnification of (a) 1.25 kx and (b) 4.00 kx.
Coatings 14 01125 g006
Coatings 14 01125 g007
Figure 7. (a) XRD diffractogram of the pre-coating and (b) stick pattern for nickel (ICDD 04-010-6148).
Figure 7. (a) XRD diffractogram of the pre-coating and (b) stick pattern for nickel (ICDD 04-010-6148).
Coatings 14 01125 g007
Coatings 14 01125 g008
Figure 8. Surface SEM micrographs of the pre-coating, with a magnification of (a) 500×, (b) 2000× and (c) 5000×.
Figure 8. Surface SEM micrographs of the pre-coating, with a magnification of (a) 500×, (b) 2000× and (c) 5000×.
Coatings 14 01125 g008
Coatings 14 01125 g009
Figure 9. Superficial feature size distribution histogram determined from the SEM images.
Figure 9. Superficial feature size distribution histogram determined from the SEM images.
Coatings 14 01125 g009
Coatings 14 01125 g010
Figure 10. Cross-section SEM images of the studied samples: (a) BN5, (b) BN10, (c) BN15A and (d) BN15B.
Figure 10. Cross-section SEM images of the studied samples: (a) BN5, (b) BN10, (c) BN15A and (d) BN15B.
Coatings 14 01125 g010
Coatings 14 01125 g011
Figure 11. XRD diffractograms of the coatings and the reference of the pre-coating (PC).
Figure 11. XRD diffractograms of the coatings and the reference of the pre-coating (PC).
Coatings 14 01125 g011
Coatings 14 01125 g012
Figure 12. Surface SEM micrographs of the coatings, BN5 with a magnification of (a) 500× and (b) 5000×, and BN10 with a magnification of (c) 500× and (d) 5000×.
Figure 12. Surface SEM micrographs of the coatings, BN5 with a magnification of (a) 500× and (b) 5000×, and BN10 with a magnification of (c) 500× and (d) 5000×.
Coatings 14 01125 g012
Coatings 14 01125 g013
Figure 13. Surface SEM micrographs of the coatings, BN15A with a magnification of (a) 500× and (b) 5000×, and BN15B with a magnification of (c) 500× and (d) 5000×.
Figure 13. Surface SEM micrographs of the coatings, BN15A with a magnification of (a) 500× and (b) 5000×, and BN15B with a magnification of (c) 500× and (d) 5000×.
Coatings 14 01125 g013
Coatings 14 01125 g014
Figure 14. SEM image of BN15A surface at (a) 1474×; EDS spectra of sample BN15A, with WS2 nanoparticles: (b) superficial protrusion, (c) compromised surface area and (d) area without defects.
Figure 14. SEM image of BN15A surface at (a) 1474×; EDS spectra of sample BN15A, with WS2 nanoparticles: (b) superficial protrusion, (c) compromised surface area and (d) area without defects.
Coatings 14 01125 g014
Coatings 14 01125 g015
Figure 15. The 2D and 3D AFM images (10 µm × 10 µm) of the coatings: (a) BN5 and (b) BN10.
Figure 15. The 2D and 3D AFM images (10 µm × 10 µm) of the coatings: (a) BN5 and (b) BN10.
Coatings 14 01125 g015
Coatings 14 01125 g016
Figure 16. CIE L*a*b* colour diagram of the pre-coating (PC) and black coatings.
Figure 16. CIE L*a*b* colour diagram of the pre-coating (PC) and black coatings.
Coatings 14 01125 g016
Coatings 14 01125 g017
Figure 17. Surface SEM micrographs of wear tracks on coating (a) BN5 and (b) BN10.
Figure 17. Surface SEM micrographs of wear tracks on coating (a) BN5 and (b) BN10.
Coatings 14 01125 g017
Coatings 14 01125 g018
Figure 18. Tribological properties of coatings and pre-coating (PC): friction coefficient.
Figure 18. Tribological properties of coatings and pre-coating (PC): friction coefficient.
Coatings 14 01125 g018
Table 1. Electrolyte composition and electrodeposition parameters.
Table 1. Electrolyte composition and electrodeposition parameters.
Pre-CoatingCoating
ReagentsConcentration (g/L)Concentration
(g/L)
NiCl2.6H2O (98%, Thermo Scientific, Waltham, MA, USA)75.3375.33
NaCl (≥99%, Sigma-Aldrich, St. Louis, MO, USA)30.0030.00
H3BO3 (≥99.8%, Fisher Chemical, Pittsburgh, PA, USA)26.67------
Deposition parameters
T (°C)Room temperatureRoom temperature
t (min)55 and 10
J (mA/cm2)273
w (rpm)200200
pH4.83–4.936.40–6.50
Table 2. CTAB and WS2 concentrations for samples BN15A and BN15B.
Table 2. CTAB and WS2 concentrations for samples BN15A and BN15B.
BN15ABN15B
AdditivesConcentration (g/L)
WS2 (>99.99%, Nanografi, Ankara, Turkey)2.67------
CTAB (>9%, Acros Organics, Geel, Belgium)0.050.10
Table 3. Atomic concentration of Ni and O, obtained by EDS analysis of the pre-coating.
Table 3. Atomic concentration of Ni and O, obtained by EDS analysis of the pre-coating.
ElementAtomic Concentration (%)
Ni98
O2
Table 4. Atomic concentration of Ni and O, obtained by EDS analysis of the coatings.
Table 4. Atomic concentration of Ni and O, obtained by EDS analysis of the coatings.
SampleAtomic Concentration (%)
NiO
BN56733
BN106436
Table 5. Sa values measured by AFM.
Table 5. Sa values measured by AFM.
SampleSa ± SD
(nm)
BN598 ± 9
BN1059 ± 5
Table 6. CIE L*a*b* colour coordinates of the pre-coating (PC) and black coatings.
Table 6. CIE L*a*b* colour coordinates of the pre-coating (PC) and black coatings.
SampleL*
PC76.70 ± 0.17%
BN526.65 ± 0.15%
BN1024.65 ± 0.16%
BN15A28.13 ± 0.11%
BN15B26.65 ± 0.04%
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Santos, G.; Benzarti, Z.; Cavaleiro, D.; Figueiredo, L.; Carvalho, S.; Devesa, S. Optimization of Black Nickel Coatings’ Electrodeposit onto Steel. Coatings 2024, 14, 1125. https://doi.org/10.3390/coatings14091125

AMA Style

Santos G, Benzarti Z, Cavaleiro D, Figueiredo L, Carvalho S, Devesa S. Optimization of Black Nickel Coatings’ Electrodeposit onto Steel. Coatings. 2024; 14(9):1125. https://doi.org/10.3390/coatings14091125

Chicago/Turabian Style

Santos, Gabriel, Zohra Benzarti, Diogo Cavaleiro, Luís Figueiredo, Sandra Carvalho, and Susana Devesa. 2024. "Optimization of Black Nickel Coatings’ Electrodeposit onto Steel" Coatings 14, no. 9: 1125. https://doi.org/10.3390/coatings14091125

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop