Effect of TiC Addition on Microstructure and Performances of Double Pulse Electrodeposited Ni-TiC Coatings

Abstract

Nickel–titanium carbide (Ni-TiC) coatings were synthesized on Q235 steel via double-pulse electrodeposition to enhance surface properties. The influence of TiC concentration on surface morphology, microstructure, and performance was systematically studied using SEM, TEM, XRD, microhardness testing, wear analysis, and electrochemical methods. At low TiC concentrations (2–4 g/L), the coatings exhibited typical cell-like morphology. At 8 g/L, the coating showed a dense structure, refined grains, and broad Ni diffraction peaks. TEM analysis revealed nickel and TiC grain sizes of 97.82 nm and 34.75 nm, respectively. The plating rate remained stable (~36.94 mg·cm⁻²·h⁻¹), while surface roughness increased with TiC content. The 8 g/L TiC coating achieved the highest microhardness (743.13 HV), lowest wear loss (5.43%), and superior corrosion resistance, with a self-corrosion current density of 5.27 × 10⁻⁶ A·cm⁻² and polarization resistance of 7705.62 Ω·cm². These enhancements are attributed to uniform TiC dispersion and grain boundary pinning. Thus, 8 g/L TiC is optimal for fabricating Ni-TiC coatings with improved mechanical and electrochemical performance. This work demonstrates a practical strategy for developing high-performance Ni-based composite coatings via double-pulse electrodeposition.

1. Introduction

Ni-based coatings, known for their excellent mechanical strength, chemical inertness, and wear resistance, have proven highly valuable in various industrial applications, including automotive manufacturing, chemical processing, and metallurgical equipment [1,2,3]. However, as modern industrial applications demand increasingly advanced surface properties, traditional Ni-based coatings are no longer sufficient to meet performance requirements under extreme operating conditions [4,5,6,7]. Studies have demonstrated that incorporating a reinforcing phase can significantly improve coating performance, with different reinforcement materials tailored to improve specific functional properties [8,9,10,11]. Ma et al. [12] successfully fabricated Ni-TiC coatings on 42CrMo steel via electrodeposition. They found that Ni-TiC coatings demonstrated significant improvement in wear resistance in comparison with Ni-P coatings. Cai et al. [13] employed atmospheric plasma spraying to fabricate Ni60A-Ti₃AlC₂ coatings on Ni-Cr stainless steel substrates with different Ti₃AlC₂ additions. The results showed that with 20 wt% Ti₃AlC₂, the coatings revealed the smallest defects and the lowest porosity. Ogunbiyi et al. [14] used spark plasma sintering to produce AZ91D–Ni–graphene nanoparticle (GNP)–magnesium matrix composites. The experimental results showed that the microhardness of the composite was 89.7 HV, nanohardness was 18,251.3 MPa, the modulus of elasticity was 243.75 GPa, and the wear rate was 3.85 × 10⁻³ mm³·N⁻¹·m⁻¹ at 2 wt% GNPs. Among various reinforcement systems, the carbide ceramic phase has garnered significant attention due to its excellent compatibility with the metal matrix. Using TiC nanoparticles as an example, their high melting point, hardness, and exceptional thermodynamic stability significantly increase the wear resistance and high-temperature performance of the coating. Similarly, the low interfacial energy between TiC and the nickel matrix promotes uniform particle dispersion, effectively preventing stress concentration [15,16,17].

The development of Ni-based coatings preparation technologies has diversified, with key methods including chemical vapor deposition, laser cladding, and electrodeposition. Among these, electrodeposition has emerged as one of the most widely adopted techniques in industrial applications due to its key advantages, such as precise and controllable process parameters, low equipment investment costs, and broad substrate adaptability [18,19,20,21]. Zafarghandi et al. [22] synthesized nickel-teflon (Ni-PTFE) coatings through electrodeposition, and the results showed that at a PTFE concentration of 15 g/L, the resulting coating showed a layered morphology, with a maximum contact angle of 158° and the lowest corrosion current density of 0.03 μA/cm². Akbarpour et al. [23] successfully produced Ni-Co/SiO₂ nanocoatings using pulse electrodeposition and investigated the effects of SiO₂ concentration on the coatings. The results showed a 52% increase in microhardness, reaching 581 HV, and a significant reduction in the coefficient of friction compared to the coating without SiO₂. Zhang et al. [24] prepared Ni-Y₂O₃-MgO nanocoatings with different Y₂O₃ concentrations on Q235 steel surfaces using pulse electrodeposition. The results showed that at a Y₂O₃ concentration of 10 g/L, the coating displayed the best surface quality, highest self-corrosion potential, lowest self-corrosion current density, and minimal corrosion loss. Liu et al. [25] fabricated a Ni-MoS₂ composite coating on AISI 1020 steel substrate by thermal spraying method and investigated its wear resistance. The experimental results showed that the weight loss of the Ni-MoS₂ composite coating was the least under low loads (<15 N), but it increased rapidly with increases in load (>30 N). Gana et al. [26] selected low-carbon steel alloy as the substrate and investigated the effect of current density on the electro-deposition of Ni-MoS₂ composite coating. The results showed that all Ni-MoS₂ samples were harder than the low-carbon steel substrate.

Electrodeposition technology includes several methods, including direct current electrodeposition (DCE), pulse electrodeposition (PE), jet electrodeposition (JE), and ultrasonic electrodeposition (UE). Compared to conventional direct current and single pulse processes, double pulse electrodeposition (DPE) offers improved coating performance due to the synergistic effects of forward and reverse pulses, making it a promising technique with wide application potential. During the forward pulse, the high current density accelerates the deposition of metal ions and promotes the formation of an ultrafine grain structure, greatly improving the coating’s densification. However, the reverse pulse helps to remove surface burrs and reduce roughness through anodic dissolution, achieving a mirror-like finish. Moreover, it replenishes the concentration of metal ions in the cathode region, effectively alleviating the effects of concentration polarization. Wang et al. [27] prepared silver chloride on an aluminum foil substrate through dual-pulse electrodeposition and applied it for marine electric field measurement. The research results revealed the correlation between the electrochemical behavior of the electrode and its surface physical properties. Fang et al. [28] prepared Ni-GQDs nanocomposite coatings under supercritical CO₂ conditions through dual-pulse electrodeposition, and investigated the influence of reverse pulse current density on the microstructure and morphology of the Ni-GQDs nanocomposite coatings. The results showed that when the reverse pulse current density was 0.8 A/dm², the surface of the Ni-GQDs-II nanocomposite coating was dense and flat, with GQDs uniformly dispersed in the coating, and GQDs were closely bonded to the Ni grains. Current studies on the preparation of Ni-based coatings using pulse electrodeposition have focused on the single pulse process, with less attention given to the double pulse technique. Therefore, this study aims to address this gap by using TiC as the reinforcing phase particles. Ni-TiC nanocoatings were fabricated on the surface of Q235 steel using DPE. Techniques such as scanning electron microscopy (SEM), (transmission electron microscopy) TEM, (X-Ray diffraction) XRD, and electrochemical testing were employed to investigate the effects of TiC concentration on the properties of the resulting coatings.

2. Experiments

2.1. Materials

TiC nanoparticles (99.9% purity, with a particle size range of 30–50 nm) were provided by Beijing Xinke Nanotechnology Co., Ltd. (Beijing, China). The pretreatment process for the Q235 steel substrate involved several steps. First, the specimens (30 mm × 30 mm × 4 mm) were leveled on the surface, then progressively sanded using 400# to 2000# sandpapers to achieve a uniform surface morphology. Chemical cleaning was then performed by immersing the specimens in a 10 wt% NaOH solution for 15 min to remove grease, followed by a 15 wt% HCl solution for 30 s to activate the surface. Finally, the samples were thoroughly rinsed with deionized water in multiple stages to ensure a clean surface for the subsequent electrodeposition process. All reagents involved in the experiment were of analytical purity and purchased from Beijing Purui’ao Company (Beijing, China).

2.2. Preparation

Based on a series of preliminary experiments, the electrolyte composition and deposition parameters for fabricating Ni-TiC composite coatings via double-pulse electrodeposition (DPE) are detailed in

Table 1. Composition of plating solution.

Composition	Concentration (g/L)
NiSO4·6H2O	240
NiCl2·6H2O	30
H3BO3	35
C12H25SO4Na	0.1
C7H5NO3S	1.5
TiC nanoparticles	2–16

and

Table 2. Process parameters.

Parameter	Value
Forward reverse duty cycles (Jm+)	5 A/dm2
Reverse average current densities (Jm−)	−1.4 A/dm2
Forward reverse duty cycles (D+)	50%
Reverse duty cycles (D−)	10%
$\mathrm{Forward}\mathrm{pulse}\mathrm{periods}(t_{pulse}^{+}$)	5 ms
$\mathrm{Reverse}\mathrm{pulse}\mathrm{periods}(t_{pulse}^{-})$	1 ms
Bath temperature (T)	50 °C
pH	3.5
Stirring rate v	200 r/min
Plating time ttotal	50 min

. In the plating bath, NiSO₄·6H₂O was used as the main source of Ni²⁺ ions, while NiCl₂·6H₂O provided Cl⁻ ions to enhance conductivity. H₃BO₃ served to buffer the pH, C₇H₅NO₃S acted as a brightener to improve the surface smoothness of the coating, and C₁₂H₂₅SO₄Na was introduced as an anionic surfactant to suppress pinhole formation and improve dispersion stability.

Electrodeposition experiments were conducted with Q235 steel as the cathode and pure nickel plate as the anode. To investigate the influence of TiC concentration, five levels of TiC nanoparticle additions (2, 4, 8, 12, and 16 g/L) were selected [29]. The DPE method employed in this study consists of periodic cycles of forward and reverse current pulses. During the forward (cathodic) phase, a current density of +5 A/dm² was applied for 5 ms with a 50% duty cycle, promoting the deposition of Ni and co-deposition of TiC particles. In the reverse (anodic) phase, a current density of −1.4 A/dm² was applied for 1 ms with a 10% duty cycle. This anodic pulse removes loosely adhered particles and suppresses surface defects such as dendrites or nodules. The full waveform is illustrated in Figure 1, and was programmed using a digital pulse power controller to ensure stable and repeatable deposition conditions across all experimental groups.

The total deposition time for each sample was 50 min. During the process, the bath temperature was maintained at 50 °C, the pH was adjusted to 3.5, and continuous magnetic stirring at 200 rpm was applied to prevent nanoparticle agglomeration and ensure uniform particle suspension throughout the electrolyte.

2.3. Characterization

In this study, various analytical techniques were employed to characterize the coating specimens. Surface morphology was investigated using a JSM-3400 scanning electron microscope (SEM, JEOL Co., Ltd., Tokyo, Japan), while the microstructure was analyzed with a JEM-ACE200F transmission electron microscope (TEM, JEOL Co., Ltd., Tokyo, Japan). The phase composition was determined using an XRD-6100 X-ray diffractometer (Shimadzu Co., Ltd., Kyoto, Japan) with Cu Kα radiation (λ = 0.154178 nm), operating at 40 kV and 30 mA. XRD scans were conducted over a 2θ range of 20°–80° at a continuous scanning rate of 10°/min with 0.02° step increments. Surface roughness was assessed using an OLS4000 laser confocal microscope (LSCM, Olympus Co., Ltd., Tokyo, Japan), with R_a values obtained through data fitting for comparative analysis. Microhardness measurements were carried out using an HV-50 rotating turret microhardness tester (Jinan Wester Test Equipment Co., Ltd., Jian, China) under a 100 g load for 10 s. Ten parallel measurements were taken at 3 mm intervals along the coated surface and averaged. Abrasive wear properties were evaluated using an ML-100 wear tester at room temperature (25 °C) under a 0.5 kg load for 3 min, with weight measurements recorded every 30 s. The electrochemical performance was evaluated using a CHI660E electrochemical workstation (Shanghai Huachen Equipment Co., Ltd., Shanghai, China) through Tafel polarization and electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl solution. EIS measurements were conducted using a ±10 mV sinusoidal excitation signal over a frequency range of 10⁵ to 10⁻² Hz.

3. Results and Discussions

3.1. Surface Morphology

The surface morphologies of Ni-TiC nanocoatings with different TiC concentrations were observed using SEM, as shown in Figure 2. The SEM images revealed a ‘polarization’ phenomenon due to the different TiC particle concentrations in the plating solution. At lower TiC concentrations, the surfaces of the fabricated coatings were relatively flat and dense, displaying a typical cellular structure (Figure 2a,b). When the concentration of TiC nanoparticles increased to 8 g/L, the highly active particles altered the Ni deposition behavior on the substrate, resulting in a transition from a cellular to a cauliflower-like surface structure [30]. Each cauliflower-like unit consisted of multiple uniformly sized cellular components (Figure 2c). However, with further increases in TiC concentration, uneven deposition became apparent, leading to the disruption of the cauliflower-like structure and an increased agglomeration of particles on the coating surface (Figure 2d,e).

3.2. Microstructure

The TEM images of Ni-TiC coatings deposited at different TiC concentrations are shown in Figure 3. The results indicate that TiC concentration significantly influenced the microstructural features. At low concentrations, TiC particles were sparsely dispersed within the nickel matrix, revealing a broad particle size distribution. The interparticle spacing remained large, and well-defined polygonal grain boundaries of nickel were visible in certain regions. This suggests that, at lower TiC levels, the particles had a limited inhibitory effect on the growth of nickel grains [31]. Due to the insufficient content of TiC particles, the TEM images revealed visible nickel grain structures in certain regions, along with the presence of a few pores (Figure 3a,b). At an optimal TiC concentration (8 g/L), the particle density increased markedly, and the size distribution became more uniform. The nickel matrix grains were refined, and a continuous TiC particle network structure formed along the grain boundaries, tightly bonded to the nickel matrix interface without evident defects. The average diameters of nickel grains and TiC particles in Ni-TiC coatings were 97.82 nm and 34.75 nm, respectively. This improvement is attributed to the ability of the pulse current to promote uniform co-deposition of TiC particles (Figure 3c). At excessively high TiC concentrations, TEM images revealed increased particle agglomeration with blocky aggregates, significantly larger nickel grain sizes, and blurred grain boundaries (Figure 3d,e). In some regions, nickel grains encapsulated undispersed TiC particles, indicating that the excessive particle content exceeded the co-deposition threshold, therefore diminishing particle dispersion [32].

3.3. Phase Composition

The X-ray diffraction (XRD) patterns of Ni-TiC nanocoatings prepared with different TiC concentrations are presented in Figure 4. All coatings displayed characteristic peaks corresponding to Ni, specifically the (111), (200), and (220) crystal planes, with preferred orientation along the (200) plane. As the TiC concentration increased, the relative intensities of the Ni diffraction peaks—particularly the (111) plane—gradually increased, suggesting an increased relative content of Ni in the coatings with higher TiC concentrations [33].

At TiC concentrations of 2 and 4 g/L, the diffraction peaks of TiC were not detected, likely due to insufficient content in the coatings to be captured by XRD. However, as the TiC concentration increased from 8 to 16 g/L, the intensity of the TiC diffraction peaks gradually increased, indicating that a larger number of TiC nanoparticles were embedded within the coatings and detected during the XRD measurements. In Ding et al.’s report on the interface bonding characteristics of ceramic reinforcement phases and metal matrix in metal matrix composites, they also reached similar conclusions as those in this paper [34].

3.4. Surface Roughness

Table 3. Surface roughness of Ni-TiC coatings obtained with different TiC concentrations.

TiC Concentration (g/L)	Ra (μm)
2	2.28
4	2.76
8	3.43
12	4.45
16	6.84

presents the surface roughness (R_a) of the Ni-TiC coatings measured using laser confocal microscopy. The R_a increased progressively with rising TiC concentration in the plating solution. As the concentration increased, R_a shifted from a relatively flat interval at low concentrations to a steep growth interval at higher concentrations. This phenomenon is closely linked to the evolution of the coating’s micromorphology. At low concentrations (Figure 5a,b), the TiC particles were doped in limited amounts, and the coatings maintained the typical cytosolic deposition characteristics of the nickel substrate, resulting in high surface flatness. As the concentration increased to the middle–high range (Figure 5c,d), the accumulation of TiC particles led to the formation of diffusely distributed nanoscale bumps on the surface of the coatings. This particle enhancement effect directly contributed to the progressive increase in surface roughness. At very high concentrations (Figure 5e), particle agglomeration and deposition inhomogeneity were increased, leading to the formation of micrometer-scale clusters on the coating surface. This caused a substantial increase in the roughness index. The observed concentration-dependent roughness behavior was closely linked to the distribution of TiC particles within the coating and the kinetics of the deposition process [35].

3.5. Plating Rate and Microhardness

The plating rate and microhardness of Ni-TiC nanocoatings at different TiC concentrations are shown in Figure 6. TiC concentration had minimal effect on the plating rate, which remained around 36.94 mg·cm⁻²·h⁻¹, which might be related to the dominant role of the ion migration rate and current efficiency during electrodeposition. However, the microhardness of the coatings initially increased and then decreased with higher TiC concentrations. The maximum microhardness value of 743.13 HV was achieved when the TiC concentration in the plating solution was 8 g/L. Kumar et al. [36], when investigating the wear resistance of the Al-Ni-TiC composite coating, also mentioned the above conclusion. The microhardness of the coating is closely linked to the hardness of the base metal layer, the surface condition of the coating, and the content and dispersion of the second-phase particles. In this case, the variations in microhardness were primarily due to the different contents and dispersion of TiC nanoparticles within the coatings.

At low TiC concentrations in the plating solution, fewer TiC nanoparticles were incorporated into the coating, resulting in lower microhardness. An increase in TiC nanoparticle concentration to an optimal level led to improved particle content and dispersion within the coating, which significantly increased microhardness through diffusion strengthening and fine crystal strengthening. However, excessive TiC concentration promoted nanoparticle agglomeration, increasing the probability of poorly bonded aggregates being incorporated into the coating. These loosely bonded agglomerates were susceptible to fracture under external force, reducing coating densification and compromising the strength of the continuous phase, ultimately leading to a decline in microhardness [37,38].

3.6. Wear Resistance

The wear mass loss ratio of Ni-TiC coatings at different TiC concentrations is illustrated in Figure 7. As TiC concentration increased, the wear mass loss ratio initially declined and then rose, reaching a minimum of 5.43% at 8 g/L. At lower concentrations, the limited co-deposition of TiC nanoparticles resulted in insufficient particle reinforcement, leading to higher wear mass loss. When the TiC concentration reached an optimal range, the TiC particles were more evenly distributed throughout the coating, increasing its hardness and providing better support during friction, thus reducing direct contact wear. However, excessive TiC concentration led to particle agglomeration on the coating’s surface. These agglomerates, with a loose structure and weak bonding, were more prone to abrasion during friction, causing spalling wear and, consequently, an increase in the wear mass loss ratio [39].

3.7. Corrosion Resistance

The polarization curves and electrochemical impedance spectra (Nyquist plots) of Ni-TiC nanocoatings with different TiC concentrations are shown in Figure 7. According to the Tafel polarization curves (Figure 8a), the coatings fabricated with lower TiC concentrations showed significantly higher self-corrosion potentials (E_corr) compared to the coating prepared with 16 g/L TiC. The highest E_corr value was recorded for the coating produced at a TiC concentration of 8 g/L, indicating a reduced driving force for corrosion under these conditions. Additionally, the corresponding Tafel curves have been fitted using nonlinear regression (solid lines), and the high level of overlap between the experimental and fitted data confirms the excellent fitting quality, thus validating the accuracy of the extracted electrochemical parameters. The Nyquist plots (Figure 8b) for each coating showed a single capacitive arc, reflecting surface inhomogeneity and resulting in a dispersion effect. The corresponding equivalent circuit model fitting (solid lines in the figure) shows a close match with the experimental data, indicating good reliability of the fitted values, including with regard to polarization resistance (R_p). With increasing TiC concentration in the plating solution, the arc resistance radius initially increased and then decreased, reaching a maximum of 8 g/L, indicating that the coating produced under this condition displayed the highest resistance to chloride ion (Cl⁻) invasion.

Table 4. Fitting results of Tafel polarization curve parameters.

TiC Concentration (g/L)	Ecorr (V)	Rp (Ω·cm2)	Jcorr (A·cm−2)
2	−0.18	1635.78	2.51 × 10−5
4	−0.21	2088.93	2.02 × 10−5
8	−0.11	7705.62	5.27 × 10−6
12	−0.23	1677.44	2.36 × 10−5
16	−0.45	1109.31	3.92 × 10−5

presents the fitting results of Tafel polarization curves for each coating. At a TiC nanoparticle concentration of 8 g/L, the coating revealed a self-corrosion current density (J_corr) of 5.27 × 10⁻⁶ A·cm⁻², which was an order of magnitude lower than the other coatings. The corresponding (E_corr) and linear (R_p) values were −0.11 V and 7705.62 Ω·cm², respectively, both significantly higher than those of the other coatings. These findings, align with the electrochemical impedance spectroscopy results, suggest that the TiC concentration’s effect on corrosion resistance is primarily due to the content, distribution, and densification of TiC particles in the coating. As the concentration of TiC nanoparticles in the plating solution increased, the probability of TiC nanoparticles entering the coating during the electrodeposition process also increased. This led to a higher content of TiC particles in the coating. The fine nanoparticles were pinned at the grain boundaries, dislocations, and other defects in the Ni coating, which inhibited grain growth and resulted in grain refinement. Simultaneously, these TiC particles effectively impeded the infiltration of corrosive Cl⁻ ions, therefore preventing further corrosion of the substrate Ni coating [40].

4. Conclusions

In this study, Ni-TiC composite coatings were successfully fabricated via double-pulse electrodeposition, and the influence of TiC concentration on their microstructure and performance was systematically investigated. At low TiC concentrations (2–4 g/L), the coatings exhibited a typical cell-like deposition structure. With increasing TiC content, the morphology transitioned to a cauliflower-like structure, and at 8 g/L, the coatings showed higher surface density and significant grain refinement. XRD analysis revealed that TiC diffraction peaks were not detected at lower concentrations, but became increasingly evident as the TiC concentration rose from 8 to 16 g/L. The coating deposited at 8 g/L displayed the most refined structure, with average grain sizes of 97.82 nm for nickel and 34.75 nm for TiC particles. This optimal concentration also corresponded to the best overall properties, including the highest microhardness of 743.13 HV, the lowest wear mass loss ratio of 5.43%, a self-corrosion potential of −0.11 V, and a minimum self-corrosion current density of 5.27 × 10⁻⁶ A·cm⁻² in 3.5 wt% NaCl solution. These results confirm that a TiC concentration of 8 g/L is optimal for enhancing both mechanical and electrochemical performance in Ni-TiC coatings using the double-pulse electrodeposition method.