Electrodeposition of a Ni–P–TiO₂/Ti₃C₂T_x Coating with In Situ Grown Nanoparticles TiO₂ on Ti₃C₂T_x Sheets

Abstract

Protective coatings have received considerable attention for the surface treatment of devices. Herein, in situ grown nanoparticles, TiO₂ on Ti₃C₂T_x sheets (TiO₂/Ti₃C₂T_x), are prepared by a simple hydrothermal oxidation method possessing the layer structure, which is applied to prepare protective coatings. The Ni–P–TiO₂/Ti₃C₂T_x coating is prepared by electroplating technology, revealing more excellent properties than those of the Ni–P coating. Compared with the Ni–P coating, even though the Ni–P–TiO₂/Ti₃C₂T_x coating holds the rough surface, the wettability is changed from hydrophilic to hydrophobic, owing to the gathering existence of TiO₂/Ti₃C₂T_x on the surface and coarse surface texture. In addition, the participation of TiO₂/Ti₃C₂T_x in the Ni–P coating can improve the capacity of corrosion prevention and decrease the corrosion rate. According to the results of hardness and wear tests, microhardness of the Ni–P–TiO₂/Ti₃C₂T_x coating is approximately 1350 kg mm⁻² and the coefficient of friction (COF) of Ni–P–TiO₂/Ti₃C₂T_x coatings is about 0.40, which is much lower than that of Ni–P coatings. Thus, the Ni–P–TiO₂/Ti₃C₂T_x coating can be a promising material to protect the surface of equipment.

1. Introduction

It is well known that the surface is the most essential part of several engineering components, easily suffering from corrosion, abrasion, and fatigue [1,2]. Researchers have made great efforts to improve these surface properties, such as hardness, wear performance, and corrosion resistance [3,4]. Similarly, various technologies have been employed to prepare the protective coating, including electroplating, plasma thermal spray, and chemical vapor deposition [5]. Due to low cost and easy operation, electroplating is the most outstanding among these technologies [6,7,8,9].

According to previous papers, the Ni–P composite coating possesses excellent properties, so it is widely used to deal with problems in the engineering process [10,11]. However, when encountering some tricky conditions, the Ni–P composite coating is hardly able to overcome these difficulties [12]. Thus, the modification of Ni–P composite coatings is proven to be an efficient method to expand application fields, so introducing particles into these coatings can improve their properties, such as TiO₂ particles, MoS₂ particles, and Al₂O₃ particles [13,14,15,16]. Generally, the property of the composite coating is closely related to these incorporating particles [17].

Usually, two-dimensional (2D) structural materials hold a low friction coefficient, so they can show promising prospects in solid lubrication. As a typical layered structural material, Ti₃C₂T_x particles have been applied to lubricating oil, owing to wear resistance, thermal stability, and electrochemical corrosion [18]. Due to the weak Van der Waal’s bonding between layers, there is potential for Ti₃C₂T_x particles to slide, so it holds a low friction coefficient of 0.1 in lubricating oil. Thus, these incorporating Ti₃C₂T_x particles can provide a low friction coefficient for the Ni–P coating [19]. As previous papers have shown, TiO₂ particles introduced into coatings can increase the hardness, wear resistance, and corrosion resistance. Baghery et al. prepared the Ni–TiO₂ coating, which exhibited excellent properties of hardness and wear resistance [2]. Similarly, Uttam and Duchaniya synthesized the Ni–P–TiO₂ coating on mild steel, showing excellent corrosion resistance [20]. Therefore, it is a perfect idea for introducing TiO₂ particles into the Ni–P coating.

TiO₂/Ti₃C₂T_x particles with heterogeneous interfaces have been widely used in photocatalytic activity and electrochemistry. In previous works, Xu et al. prepare in situ grown nanocrystal TiO₂ on 2D Ti₃C₂ nanosheets for artificial photosynthesis of chemical fuels [21]. Peng et al. found that hybrids of two-dimensional Ti₃C₂ and TiO₂ exposing {001} facets enhanced photocatalytic activity [22]. However, it is little reported that TiO₂/Ti₃C₂T_x particles are used in the area of surface treatment. In this work, in situ grown nanocrystal TiO₂ on Ti₃C₂T_x particles were prepared by hydrothermal reaction and incorporated into Ni–P coatings to prepare the Ni–P–TiO₂/Ti₃C₂T_x coating. These particles can combine excellent properties with TiO₂ and Ti₃C₂T_x, so it is beneficial to improve the wear resistance and corrosion resistance of the Ni–P coating.

2. Experiment Procedure

2.1. Preparation of TiO₂/Ti₃C₂T_x Powders

Ti₃AlC₂ powders (10 g) were transferred to a Teflon beaker, and 40 mL 40% hydrofluoric acid were dropwise added into them under stirring at 40 °C for 18 h. Then, these obtained products were washed with deionized water until a pH of 5 and dried in a vacuum drying oven at a temperature of 80 °C for 24 h [18].

Those as-prepared products (2.4 g) were added to a beaker, containing 360 mL 1M hydrochloric acid and 7.2 g sodium fluoroborate under agitation for 30 min. The obtained solution was shifted into hydrothermal reactors at 160 °C for 12 h. After washing with deionized water several times, these products were shifted to a vacuum drying oven at 80 °C for 24 h.

2.2. Preparation of Composite Coatings

TiO₂/Ti₃C₂T_x powders (4 g·L⁻¹) were dispersed uniformly into nickel sulfate plating baths, including nickel sulfate, nickel chloride, boric acid, citric acid, and SDS under stirring. The bath compositions and experimental conditions are shown in

Table 1. Bath compositions and experimental conditions.

Compositions	Experimental Conditions
Nickel sulfate	250 g L−1
Nickel chloride	40 g L−1
Boric acid	40 g L−1
Citric acid	45 g L−1
Sodium hypophosphite	30 g L−1
TiO2/Ti3C2Tx powders	4 g L−1
SDS	1 g L−1
pH	3–4
Current condition density	2 A dm−2
Time	1 h
Temperature	50 °C
Magnetic stirring speed	600 rpm

. A pure nickel plate (70 mm × 60 mm) and manganese steel (20 mm × 30 mm) were taken as the anode and cathode, respectively. The composition of the manganese steel is shown in Figure 1, mainly containing elements of Fe, Mn, Cr, Si, S, and P. After the process of electroplating, the composite coating was washed by ultrasound for 10 min, dried in an oven at 100 °C for 1 h, and then annealed in a tube furnace at 400 °C for 60 min under argon atmosphere.

2.3. Material Characterization

Field-emission scanning electron microscopy (FE-SEM, JEOL JSM-6700F, JEOL, Tokyo, Japan) and a transmission electron microscopy (TEM, JEOL JEM-2010F, JEOL, Tokyo, Japan) equipped with an accelerating voltage of 200 kV were employed to observe the morphology and structure of these samples. X-ray diffractometer (XRD, Philips, X’Pert Pro, Almelo, the Netherlands) with Cu-Kα radiation and X-ray fluorescence spectrometer (XRF; AXIOS-MAX, PANalytical B.V., Almelo, the Netherlands) were used to measure the chemical composition of samples. A laser-scanning Raman microscope (Nanophoton Corporation, Raman-11, Osaka, Japan) was applied to detect the structure of samples with a confocal laser spectrometer, using the 532 nm excitation of the argon laser at room temperature. X-ray photoelectron spectroscopy (XPS, Themo Fisher Scientific, ESCALAB 250Xi, Waltham, MA, USA) with a monochromatic Al Kα radiation was used to record the surface analysis of TiO₂/Ti₃C₂T_x powders. The Fourier transform infrared (FTIR, Excalibur 3100, Varian Medical Systems, Palo Alto, CA, USA) spectroscopy measurement was conducted in a KBr pellet at room temperature. A digital micro-hardness tester (MC010, Yanrui, Shanghai, China) was applied to determine the microhardness of composite coatings at a load of 300 g for 15 s, and the result was achieved from the average of five data on the sample surface. A surface roughness tester (TR211, Shidai Ruida, Beijing, China) was used to detect the Ra of composite coatings, which was obtained from the mean result of five data sets. An electrochemical station (UN-O-16076, Zahner, Kronach, Germany) was used to test the electrochemical measurement in a three-electrode system. Water contact angle measurements using 2 uL water droplets were determined by a measurement apparatus (K100, Kruss, Hamburg, Germany) at 25 °C with DropSnake to shape the drop and measure the contact angle. Wear tests were carried out by a circumrotating ball-on-disk tribometer (HT-1000, Lanzhou, China) with silicon nitride as the grinding material.

3. Results and Discussions

3.1. Characterization of Powders

Figure 2 shows the XRD pattern of TiO₂/Ti₃C₂T_x powders with TiO₂ and Ti₃AlC₂ standard patterns. Due to no information of Ti₃C₂T_x in ICSD, a Ti₃AlC₂ standard pattern with the space group P63/mmc was used to fit the XRD pattern of TiO₂/Ti₃C₂T_x powders [23]. These characteristic peaks located at 9.58° and 19.17° were assigned to (002) and (004), which shifted lower to 8.95° and 17.91°, indicating the existence of Ti₃C₂T_x. In addition, the shift of planes can show the increase of the c-lattice parameter and basal spacing. After hydrothermal oxidation, peaks belonging to anatase TiO₂ phase were much stronger than those of Ti₃C₂T_x powders, demonstrating that Ti₃C₂T_x was partly oxidized and the anatase TiO₂ was present on the Ti₃C₂T_x [22].

Raman spectra and FTIR spectra of TiO₂/Ti₃C₂T_x and Ti₃C₂T_x powders are shown in Figure 3. In Figure 3a, the strongest peak located at 150 cm⁻¹ is attributed to the symmetry vibration E_g of anatase TiO₂. Similarly, peaks of 413, 520, and 634 cm⁻¹ are assigned to the vibration mode of B_1g, A_1g, and E_g of anatase TiO₂, separately [24,25]. According to the characteristic anatase Raman peak of pure TiO₂, a slight increase in the Eg1 peak is detected [26]. The peaks are in a tetragonum in Figure 3, showing the existence of TiO₂. These peaks of anatase TiO₂ mainly appear among 800~500 cm⁻¹, so peaks of TiO₂/Ti₃C₂T_x are stronger than those of Ti₃C₂T_x. In addition, the peak located at ~570 cm⁻¹ can be assigned to the deformation vibration of the Ti–O bond. [25] Thus, these results of Raman and FTIR spectra indicate the formation of anatase TiO₂.

SEM images of Ti₃C₂T_x powders and TiO₂/Ti₃C₂T_x powders with EDS elemental mapping are clearly seen in Figure 4. In Figure 4a, the layered structure of Ti₃C₂T_x powders is obviously shown after the etching effect of HF solution. In Figure 4b, after the hydrothermal oxidation, even though anatase TiO₂ particles exist on the Ti₃C₂T_x powders, the layered structure of Ti₃C₂T_x powders still remain, deriving from the titanium atoms on Ti₃C₂T_x, acting as nucleating sites for the growth of anatase TiO₂ [27]. The HRSEM image of the circle area displays the anatase TiO₂ with a thickness of ~30 nm and length of ~200 nm, and it can be observed that the interfacial angle between the {001} and {101} facets of anatase TiO₂ is about 68.3° [28]. As for the previous paper, the percentage of the {001} facets can be calculated as about 69.8% from the schematic diagram of an anatase TiO₂ [29]. The elemental mapping results from Figure 4c show that main elements of oxygen, titanium, and carbon are present on the TiO₂/Ti₃C₂T_x powders, so it corresponds to results of the XRD pattern (Figure 2).

In Figure 5, HRTEM images show the crystal relationship of TiO₂ and Ti₃C₂T_x. Figure 5a reveals the morphology of TiO₂ with a tetragonal shape, and Figure 5b shows the growth of TiO₂ derived from Ti₃C₂T_x. In Figure 5c, the interface between TiO₂ and Ti₃C₂T_x can be clearly demonstrated by the yellow line. From Figure 5d, the result of FFT demonstrates the existence of anatase TiO₂ with crystal planes of (01-1) and (100), while it is clearly seen that the FFT result shows the presence of hexagonal Ti₃C₂T_x with crystal planes of (006) and (103) in Figure 5e. Figure 5f shows that the seamless connection of TiO₂ and Ti₃C₂T_x is due to the small discordance between {103} of Ti₃C₂T_x and {11-1} of TiO₂ [22]. These results show that TiO₂ crystals are present on the crack of Ti₃C₂T_x sheets, indicating that the nucleation of TiO₂ may exist at the defective positions of Ti₃C₂T_x. In addition, TiO₂ at the defect sites of Ti₃C₂T_x may come from hydrated Ti³⁺ ions, which are from the titanium of Ti₃C₂T_x [30,31].

From Figure 6, XPS spectra of Ti2p, C1s and O1s for Ti₃C₂T_x, and TiO₂/Ti₃C₂T_x are clearly observed. In Figure 6a, the Ti2p spectra are traced to Ti2p_3/2 and Ti2p_1/2 with four pairs and each pair separation of 5.7 eV. These peaks of Ti2p_3/2 focused on 454.9, 455.8, 456.6, and 459.4 eV are attributed to Ti–C, Ti–X, Ti_xO_y, and TiO₂, respectively. In addition, the intensity of TiO₂ becomes strong and sharp after the hydrothermal oxidation attributed to TiO₂ (Ti ions in the valence of Ti⁴⁺), while other peaks decrease, suggesting the formation of TiO₂ from Ti₃C₂T_x. As shown in Figure 6b, the C1s is fitted with five peaks, which are located at 281.6, 282.8, 284.8, 286.2, and 288.6 eV, assigned to Ti–C, C–Ti–O_a coming from the adsorbed –OH, C–C, C–O, and C–F, respectively. Due to the appearance of heterojunctions in MXene layers, the intensity of the peak is located at 281.6 eV. The hydrothermal oxidation reduces the appearance of C–Ti–O_b, derived from the interface of TiO₂ and Ti₃C₂T_x powders [32]. As for the O1s spectra in Figure 6c, four peaks of 529.4, 530.4, 531.8, and 533.3 eV are taken for adsorbed O, Ti–O–Ti, Ti–OH, and C–OH, separately [33]. Thus, this further verifies the presence of TiO₂ transformed from Ti₃C₂T_x.

3.2. Characterization of Composite Coatings

3.2.1. Compositions of Composite Coatings

XRD patterns of the Ni-P coating and the Ni–P–TiO₂/Ti₃C₂T_x coating are shown in Figure 7. It is clear to see that TiO₂ and Ti₃C₂T_x particles are introduced to the Ni–P–TiO₂/Ti₃C₂T_x coating with these characteristic peaks of 8.95° and 25.292°, respectively. After the calcination, main phases of Ni and Ni₃P are present in both coatings, but the peak intensity of the Ni phase increases with respect to the Ni₃P phase due to the participation of TiO₂/Ti₃C₂T_x particles. In addition, TiO₂/Ti₃C₂T_x particles can reduce the oriented growth of Ni, which can be determined by the following equation:

$$\mathrm{T}=\frac{{\mathit{I}}_{\left(\mathit{hkl}\right)}/{\mathit{I}}_{0\left(\mathit{hkl}\right)}}{{\sum }_{\mathit{i}=1}^{\mathit{n}}{\mathit{I}}_{\left(\mathit{hkl}\right)}/{\mathit{I}}_{0\left(\mathit{hkl}\right)}}\times 100\%$$

(1)

where I_(hkl) and I_0(hkl) represent the diffraction intensity of the sample and the standard powder, respectively. In addition, n is the number of crystal planes, and T is the indices of crystal direction. As shown in

Table 2. Crystal planes and indices of crystal direction in the Ni–P–TiO₂/Ti₃C₂T_x coating.

Crystal Planes	Indices of Crystal Direction (%)
(111)	47.17
(200)	32.39
(220)	20.44

, the indices of crystal direction for Ni phases in Ni–P–TiO₂/Ti₃C₂T_x coatings demonstrating the T of (111) are relative high, so the oriented growth plane of Ni is (111). Thus, the addition of TiO₂/Ti₃C₂T_x particles has a great effect on the composition of matrix coatings.

In Figure 8, a Raman spectrum of the Ni–P–TiO₂/Ti₃C₂T_x coating is shown with the image of the diffraction area. From Figure 8a, the addition of TiO₂/Ti₃C₂T_x makes the surface of the Ni–P–TiO₂/Ti₃C₂T_x coating rough, so the TiO₂/Ti₃C₂T_x particles tend to gather together on the surface. In Figure 8b, peaks of 150, 413, 520, and 634 cm⁻¹ are derived from TiO₂, which corresponds to the result of Figure 3a [24]. In addition, peaks located at 1380 and 1590 cm⁻¹ are assigned to D-band and G-band of Ti₃C₂T_x particles. Thus, it further verifies that the Ni–P–TiO₂/Ti₃C₂T_x coating is successfully prepared containing TiO₂/Ti₃C₂T_x particles. In Figure 8c,d, cross-section SEM images show the thickness of Ni–P coatings and Ni–P–TiO₂/Ti₃C₂T_x coatings. According to the contrast of backscattered electron imaging, the boundary between the coating and manganese steel is clear to see, so the thickness of Ni–P and Ni–P–TiO₂/Ti₃C₂T_x coatings is about 10.7 and 16.3 um, respectively.

As shown in Figure 9, the mechanism of TiO₂/Ti₃C₂T_x particles introduced into Ni–P deposits contains five steps. Cations and surfactants are absorbed into the TiO₂/Ti₃C₂T_x particle to form the clouding in the bulk layer. The clouding of charged TiO₂/Ti₃C₂T_x particles transfers to the cathode through a convection layer and diffusion layer, depending on electrophoresis in large part. The electrical double layer is close to the Ni–P composite coating, which is adsorbed and traps TiO₂/Ti₃C₂T_x particles [6,7,8]. The formation of the Ni–P coating is an induced codeposition, so reduction of nickel can lead to the reduction of phosphorus, which is beneficial for the embedding and burial of TiO₂/Ti₃C₂T_x particles into the Ni–P coating. Therefore, it is concluded that physical dispersion and electrophoretic migration participate in the formation of the Ni–P–TiO₂/Ti₃C₂T_x coating [9]. After the calcination, Ni and Ni₃P phases can be found, which is in accordance with these results of the XRD pattern (Figure 7) and Raman spectrum (Figure 8).

3.2.2. Wettability of Composite Coatings

Figure 10 shows SEM images of surface morphology for composite coatings and images of water drops. It is evident that the surface of Ni–P–TiO₂/Ti₃C₂T_x coatings is much rougher than that of Ni–P coatings, owing to the participation of TiO₂/Ti₃C₂T_x gathering on the surface. In addition, the contact angle of Ni–P–TiO₂/Ti₃C₂T_x coatings is larger than that of Ni–P coatings, indicating that the addition of TiO₂/Ti₃C₂T_x can lead to a change of wettability from hydrophilic to hydrophobic. It is well known that surface texture and surface energy can determine the surface wettability, which is important for the corrosion resistance of composite coatings [9]. Therefore, the gathering of TiO₂/Ti₃C₂T_x on the surface and the surface roughness of the composite coating are synergistic actions for the change of wettability. The result of R_a is shown in the SEM image, so it is clear to see that the incorporation of TiO₂/Ti₃C₂T_x can change the surface roughness of the Ni–P composite coating.

According to the EDS results, Ni and Ni₃P phases are uniformly distributed in the Ni–P coating, while these phases are aggregated partially. In addition, TiO₂/Ti₃C₂T_x particles are present on the surface of Ni–P–TiO₂/Ti₃C₂T_x coatings. Compared with nickel content, the incorporation of TiO₂/Ti₃C₂T_x can decrease the relative content of phosphorus for Ni–P–TiO₂/Ti₃C₂T_x coatings, which is likely to grow more active sites for nickel due to the existence of TiO₂/Ti₃C₂T_x [19].

3.2.3. Corrosion Behavior of Composite Coatings

It is shown in Figure 11 that the electrochemical measurement is conducted at room temperature. In Figure 11a, Tafel polarization curves are processed by the Tafel extrapolation method, which can obtain the data of corrosion potential (E_corr), corrosion current (i_corr), and polarization resistance (R_p). It is obvious that the corrosion current decreases and the corrosion potential transforms to positive potential of the Ni–P coating with the addition of TiO₂/Ti₃C₂T_x. In addition, the polarization resistance (R_p) of the Ni–P–TiO₂/Ti₃C₂T_x coating is higher than that of the Ni–P coating, confirming the improvement of corrosion protection for the Ni–P–TiO₂/Ti₃C₂T_x coating. As previous papers indicated, TiO₂/Ti₃C₂T_x can hinder the initiation and defect corrosion by regulating and controlling the microstructure of the composite coating [2]. Furthermore, TiO₂/Ti₃C₂T_x in the Ni–P coating can form corrosion microcells, which serve as the cathode, so it promotes the anode polarization [34,35,36]. In addition, the passive layer can be seen in the polarization curve of Ni–P–TiO₂/Ti₃C₂T_x coatings, which is good for the corrosion prevention, owing to the gathering of the TiO₂/Ti₃C₂T_x on the surface and microstructure of the surface.

Nyquist impedance diagrams of Ni–P and Ni–P–TiO₂/Ti₃C₂T_x coatings are shown in Figure 11b with the fitting equivalent circle model in Figure 11c, with the average error of 3.5%, which is investigated in the frequency range of 10⁻¹ to 10⁵. From the result of Figure 11b, it is evident that the electrochemical corrosion is mainly controlled by the diffusion process. In Figure 11c, the equivalent circuit shows the corrosion processes at the electrolyte/coatings interface. R_s stands for the solution resistance, while R_ct–CPE represents the charge transfer reaction, which is inversely proportional to the corrosion rate. In addition, CPE is a constant phase for a more accurate fit instead of a pure double layer capacitor. R_ct stands for the charge transfer resistance, so it is a measure of electron transfer across the surface. Due to the formation of nickel oxyspecies and the attack of Cl⁻, a charge transfer resistor (R_ct) is employed to stimulate these reactions [37,38]. In

Table 3. The fitting resistances of the equivalent-circuit elements.

Sample	Rs (Ω·cm2)	Rct (Ω cm2)
Ni–P coating	10.01	75.89
Ni–P–TiO2/Ti3C2Tx coating	13.08	87.69

, these fitting resistances of the equivalent-circuit elements contain R_s and R_ct. The value of R_ct is inversely proportional to corrosion rate. High R_ct of the Ni–P–TiO₂/Ti₃C₂T_x coating indicates a large corrosion resistance. From these results, it is evident that the addition of TiO₂/Ti₃C₂T_x can improve wear resistance of the Ni–P coating and decrease the corrosion rate, so it can be concluded that the participation of TiO₂/Ti₃C₂T_x can enhance the property of corrosion prevention.

3.2.4. Wear Behavior of Composite Coatings

From Figure 12, hardness and wear tests were conducted at room temperature. In Figure 12a, the fluctuation of the microhardness belonging to the Ni–P–TiO₂/Ti₃C₂T_x coating is much larger than that of the Ni–P coating, highlighting the uneven surface of the Ni–P–TiO₂/Ti₃C₂T_x composite coating with a high R_a for the gathering of TiO₂/Ti₃C₂T_x particles on the surface of Ni–P composite coatings. In addition, the microhardness of the Ni–P coating is about 680 kg·mm⁻², while that of the Ni–P–TiO₂/Ti₃C₂T_x coating is approximately 1350 kg·mm⁻², which is due to the dispersion strengthening and increasing grain boundaries hindering dislocation mobility [39,40]. Thus, the addition of TiO₂/Ti₃C₂T_x can enhance the action of dispersion strengthening and augment grain boundaries of these composite coatings, which is beneficial for the improvement of microhardness for the composite coating.

In Figure 12b, results of the wear test are carried out under the condition of dry-grinding, accompanied with a load of 2 N, duration time of 300 s, and circle radius of 1 cm. These composite coatings and the smooth silicon nitride are taken as the stationary disk and the grinding material, respectively. The average coefficient of friction for the Ni–P coating is 0.70 after wear tests, while the average coefficient of friction for the Ni–P–TiO₂/Ti₃C₂T_x coating is down to 0.40 with the participation of TiO₂/Ti₃C₂T_x. In addition, the table inserted in Figure 12b illustrates the wear loss after sliding tests, showing that the wear loss of Ni–P coatings and Ni–P–TiO₂/Ti₃C₂T_x coatings is about 2.3 mg and 0.16 mg, respectively. As previous papers have shown, high microhardness and a low coefficient of friction can simultaneously decrease the wear loss of the Ni–P–TiO₂/Ti₃C₂T_x coating [41]. Therefore, the addition of TiO₂/Ti₃C₂T_x to the Ni–P coating can improve the tribological property of this coating.

4. Conclusions

In this work, in situ grown nanoparticles TiO₂ on Ti₃C₂T_x sheets were prepared by a simple hydrothermal method. Taking the excellent property of TiO₂ and Ti₃C₂T_x into consideration, TiO₂/Ti₃C₂T_x was incorporated into the Ni–P composite coatings, which were prepared by an electroplating technique, which is little reported in this area. The following conclusions could be obtained from this study:

• The in situ grown nanocrystals TiO₂ on Ti₃C₂T_x sheets can still maintain a layered structure. The Ni–P–TiO₂/Ti₃C₂T_x coating is successfully prepared by an electroplating technique;
• The participation of TiO₂/Ti₃C₂T_x can change the wettability of Ni–P composite coatings from hydrophilic to hydrophobic;
• The Ni–P–TiO₂/Ti₃C₂T_x coating shows better properties of corrosion prevention than Ni–P coatings.
• Microhardness of the Ni–P–TiO₂/Ti₃C₂T_x coating is approximately 1350 kg mm⁻², and the coefficient of friction of Ni–P–TiO₂/Ti₃C₂T_x coatings is about 0.40, which is lower than that of the Ni–P coating.