Influence of Duty Cycle and Pulse Frequency on Structures and Performances of Electrodeposited Ni-W/TiN Nanocomposites on Oil-Gas X52 Steels

Abstract

This paper describes the pulse current electrodeposition (PCE) mediated preparation of Ni-W/TiN nanocomposites. Pulse current electrodeposition (PCE) was used to make Ni-W/TiN nanocomposites. The nanoindentation, wear, and corrosion of deposited Ni-W/TiN nanocomposites were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of pulse frequency (PF) and duty ratio on the shape, structure, phase structure, wear, and corrosion resistance of Ni-W/TiN nanocomposites was studied. When the duty cycle (DC) was 10%, the results demonstrated that a considerable number of fine grains were present on the deposited Ni-W/TiN nanocomposites, forming smooth, uniform, and fine organization. Increasing DC decreased the content of TiN nanoparticles in Ni-W/TiN nanocomposites. The content of TiN nanoparticles reduced from 11.3 wt % to 7.3 wt % by increasing the DC from 10% to 50%. In contrast, as the PF was increased, the TiN content in Ni-W/TiN nanocomposites increased. When the PF was increased from 50 Hz to 150 Hz, the TiN content increased from 6.4 wt % to 9.6 wt %, respectively. Furthermore, with a PF of 150 Hz and a DC of 10%, the produced Ni-W/TiN nanocomposites had an average hardness of 934.3 HV with ~39.8 µm of an average thickness. The weight loss of the Ni-W/TiN nanocomposites was just 17.2 mg at a PF of 150 Hz, demonstrating the excellent wear resistance potential. Meanwhile, the greatest impedance was found in Ni-W/TiN nanocomposites made with a DC of 10% and a PF of 150 Hz, indicating the best corrosion resistance.

1. Introduction

Ceramic-particle-reinforced metal-based nanocomposites (CPRMNs) have been widely utilized in compression engines and internal combustion and in petroleum tools as well as in friction parts for many years due to their excellent properties, including excellent wear resistance, high surface hardness, good cooling performance, and corrosion resistance [1,2,3,4,5,6,7,8]. CPRMNs can be made in a variety of ways, including electrodeposition, chemical deposition, and brush plating. Electrodeposition is the most successful and convenient approach for prefabricating nanocomposites [9,10,11,12]. Scholars are increasingly interested in the electrodeposition preparation of Ni-TiN-, Ni-SiC-, Ni-CeO₂-, and Cu-SiC-based nanocomposites.

From complex Ni and W ion baths, Indyka et al. [13] effectively prefabricated Ni–W nanocomposites on steel substrates. Wasekar et al. [14] used pulse current deposition to create Ni-W/SiC nanocomposites. They found that the Ni²⁺ and W⁶⁺ ions moved to the cathode surface under electric field forces and obtained electrons on the cathode surface, resulting in the form of Ni and W atoms. Zhu et al. [15] electrodeposited Ni-TiN nanocomposite on brass copper substrates. Sen et al. [16] discovered that the hardness of Ni–CeO₂ nanocomposites increased with stirring rate. Due to its superior features, such as refinement of metal grains, greater coating density, and improved plating rate, pulsed current electrodeposition (PCE) has become more extensively employed than direct current electrodeposition (DCE). The microhardness of composite coatings was directly affected by the substrate grain sizes during the PCE period, while the duty cycle (d) and pulse frequency (f) were also major factors affecting the substrate grain size. To improve the knowledge regarding structural properties and application prospects of coatings, one of the most essential tasks that should be performed is to examine the impact of plating parameters on the characteristics and microstructure of coatings.

TiN nanoparticles have a high microhardness, exceptional corrosion, and wear resistance, with enhanced thermal stability as an inorganic carbide ceramic material with extruded characteristics [17,18,19]. TiN nanoparticles can be integrated into a pure coating of metals using the PCE process, which improves the physicochemical properties of the coatings. Although many investigations on PCE and DCE electrodepositions of CPRMNs, few reports are available concerning the detailed study on the PCE-deposited Ni-W/TiN nanocomposites. In addition, it is worth studying to examine the wear and corrosion resistance of Ni-W/TiN nanocomposites on X52 steel substrates. The PCE-based preparation of Ni-W/TiN nanocomposites is reported in this research. The effect of duty cycle (DC) and pulse frequency (PF) produced by the DY-80 pulse current source on the surface topography, structure, phase structure, and wear and corrosion resistance of Ni-W/TiN nanocomposites was investigated.

2. Experimental Method

2.1. Material Preparation

The PCE method was used for the deposition of Ni-W/TiN nanocomposites on X52 steel substrates in a modified electrolyte solution [20]. The main components of the X52 steel were listed as follows: 98.49 wt % Fe, 1.05 wt % Mn, 0.22 wt % Cr, 0.20 wt % Si, 0.031 wt % C, and 0.009 wt % P. A pure Ni plate (99.98 wt %) was used as the anode, and the X52 steel (50 mm × 25 mm × 5 mm) was used as the cathode. Before PCE deposition, the X52 steel substrate was polished with 200, 400, 800, 1000, and 1500 grit sandpapers in sequence (the surface of X52 steel substrate before PCE deposition is displayed in Figure 1). Next, it was activated using 10 vol% hydroic acid for 10 s, and then distilled water was utilized to rinse the activated substrate. Afterward, the X52 steel substrate was hung in the electrolyte. The compositions of electrolyte and the electroplating parameters are described in detail in

Table 1. Electrolyte composition and electroplating parameters for depositing Ni-W/TiN nanocomposites.

Composition and Conditions	Parameters
NiSO4⋅6H2O (g/L)	220
NiCl2⋅H2O (g/L)	60
H3BO3 (g/L)	30
Na2WO4 (g/L)	60
TiN nanoparticles (g/L)	15
Plating temperature (°C)	50
pH	4.8
Pulse current density (A/dm2)	6
Duty cycle	10%, 30%, 50%
Pulse frequency (Hz)	50, 100, 150
Electroplating time (min)	50

. It was noted that when the DC was less than 10%, the Ni-W/TiN nanocomposites were severely burned. In addition, the pulse current source used in the experiment had a maximum pulse frequency of 150 Hz.

TiN nanoparticles used without modification were obtained from Daqing Tongda Nanotechnology Co., Ltd. (Daqing, Heilongjiang Province, China). Figure 2 shows the surface morphology and size distribution of TiN particles. The surface morphology of TiN particles was provided by the supplier [20]. TiN powder has a particle size of 30 nm on average. Because of the high surface energy of TiN nanoparticles, the bulk of TiN nanoparticles clump together.

2.2. Characterization

Figure 3 depicts the experimental setup utilized to manufacture the Ni-W/TiN nanocomposite [3]. A pulsed current source, electrodes (anode and cathode), a plating bath, a heater, and an ultrasonic stirrer were all included individually. The DY-80 pulsed power supply was utilized to generate a pulsed current density of 6 A/dm² during the PCE timeframe. The modified electrolyte was contained in the plating bath, and an autonomously controlled heater kept the temperature of the electrolyte at 50 °C. A DHX-500 ultrasonic stirrer was applied to keep the suspension moving and prevent TiN nanoparticles from clumping together in the electroplating solution. To eliminate any weakly attached TiN nanoparticles, all of the produced samples were rinsed through an ultrasonic stirrer for 8 ± 0.1 min.

The cross-sectional and surface morphologies of as-deposited Ni-W/TiN nanocomposites were detected using an S4800 scanning electron microscope (SEM, S4800, Hitachi High-Tech Global Network, Fukuoka, Japan). An energy-dispersive X-ray spectrometer (EDS, IE-300X) combined with SEM was used to measure the content of TiN nanoparticles embedded in the nanocomposite. A Tecnai-G2-20-S-Twin transmission electron microscope (TEM, BIONAND, álaga, Spain) was used to examine the microstructures of nanocomposites. The influence of DC and PF on the phase structure of the deposited nanocomposites was investigated using a D/Max-2400 X-ray diffractometer (XRD, D/Max-2400, Rigaku, Dusseldorf, Germany) with Cu-K radiation. A TS-75 type nanoindenter (Berkovich indenter, Alemnis, Thun, Switzerland) was used to test the microhardness of Ni-W/TiN nanocomposites. The time and applied load were set to 10 s and 100 N, respectively. The Ni-W/TiN nanocomposites were subjected to a wear test using an MR-H5A wear tester (TAHARICA, Duren Sawit, Indonesia) with a quenched steel hoop (surface hardness of 65 HRC), a rotation speed of 150 rpm, a load of 10 N, and a wear distance of 150 m. During the wear test, the steel hoop surface avoided any lubricant. A BS210S electric balance (Napco Precision Instrument Ltd., Sartorius, Germany), with a measurement precision of 0.1 mg, was used to calculate the weight loss of each Ni-W/TiN nanocomposites. Additionally, the wear morphological features of Ni-W/TiN nanocomposites were observed using an S4800 SEM. The effect of DC and PF on the Ni-W/TiN nanocomposites corrosion resistance was investigated using a three-electrode battery and a CS350 electrochemical workstation (Wuhan Corrtest Instruments Corp Ltd., Wuhan, China). In NaCl solution (3.5 wt %), the Bode and Nyquist plots of nanocomposites were obtained. The working electrode was Ni-W/TiN nanocomposites made by deposition; the reference and counter electrodes were saturated calomel electrode (SCE) and platinum foil, respectively. At 10 mV of an open-circuit voltage and 10⁻² to 10⁵ Hz of the frequency range, the electrochemical impedance spectroscopy (EIS) was performed.

3. Results and Discussion

3.1. Surface Morphology

Figure 4 depicts the morphological behavior of Ni-W/TiN nanocomposites deposited under various DCs and a 150 Hz PF. The morphologies of Ni-W/TiN nanocomposites were greatly influenced by the DC. On the deposited Ni-W/TiN nanocomposites, abundant small-sized grains were present at a DC of 10%, resulting in smooth, homogeneous, and fine microstructures (Figure 4a). When compared with nanocomposites deposited at a DC of 10%, the nanocomposites exhibited uneven and rough structures in micro-regions with greater grain sizes as the DC was increased to 30% (Figure 4b). The Ni-W/TiN nanocomposite with a DC of 50% had the largest grain size of the three nanocomposites deposited under varied DC conditions (Figure 4c). In addition, the non-uniform distribution of TiN nanoparticles was observed, which resulted in severe agglomeration.

These data can be illustrated by Equation (1):

$$d=\frac{T_{ON}}{T_{ON}+T_{OFF}}=T_{ON}f$$

(1)

where T_ON and T_OFF stand for pulse current width and pulse current interval, respectively.

The DC was directly associated with the pulse width when the PF remained constant. Because the PF of the pulse power source remained constant across DCs, the pulse width increased in proportion to the DC. Therefore, Ni²⁺ and W⁶⁺ grains constantly moved to the cathode in the plating solution. Nevertheless, because the TiN nanoparticles near the cathode were not replenished in a timely manner, the probability of Ni²⁺ and W⁶⁺ ions to capture SiC nanoparticles decreased. As a result, the content of TiN nanoparticles incorporated in the nanocomposites decreased, which also decreased the TiN nanoparticles′ influence on the fine-grain strengthening generated by the deposited coatings and metal grains [21,22]. Hence, the grain sizes of Ni and W in Ni-W/TiN nanocomposites increased as the DC increased.

Figure 5 shows the morphologies of Ni-W/TiN nanocomposites deposited at varied PFs and a 10% DC. The morphological characteristics of Ni-W/TiN nanocomposites were greatly influenced by the PF. The microstructures of the crystal grains on the nanocomposites were rough, irregular, and loose when the PF was 50 Hz. Furthermore, the TiN nanoparticles incorporated in the coatings were heavily aggregated and irregularly dispersed (Figure 5a). On the other hand, as the PF was increased to 100 Hz, modest aggregation of the nanocomposites was detected with decreased grain size (Figure 5b). However, as the PF increased from 100 to 150 Hz, the majority of TiN nanoparticles were equally distributed, resulting in nanocomposites with uniform, dense, and fine organizations (Figure 5c). Increased PF could give more energy to adsorb the insoluble nanoparticles, as revealed by previous research findings [3,8,23]. Higher frequencies resulted in homogenous binding of a significant quantity of TiN nanoparticles with Ni²⁺ and W⁶⁺ ions in Ni-W/TiN nanocomposites, increasing the deposited TiN content in the coatings, even though the DC remained constant at varied pulse frequencies. This resulted in the development of a large number of crystal nuclei, which prevented nickel grains from growing. With the increase in PF from 50 Hz to 150 Hz, the Ni-W/TiN nanocomposites had fine grains, and the microstructures became more uniform and compact.

3.2. Incorporated TiN Nanoparticles in Ni-W/TiN Nanocomposites

The mass percentages of TiN nanoparticles incorporated in Ni-W/TiN nanocomposites synthesized under various DCs and pulse frequencies are shown in Figure 6 and Figure 7, respectively. With the increase in DC from 10% to 50%, the TiN nanoparticles content decreased from 11.3 wt % to 7.3 wt % in Ni-W/TiN nanocomposites (Figure 6). Therefore, lower DC at a fixed PF implied relatively longer “OFF-time”, in which a large number of TiN nanoparticles were trapped by Ni²⁺ and W⁶⁺ ions, increasing the embedded content of TiN nanoparticles in Ni-W/TiN nanocomposites, which was in accordance with the literature [24]. However, as we increased the DC, the “OFF-time” got shorter, lowering the TiN nanoparticles content near the cathode. This led to a reduction in the content of TiN nanoparticles into the nanocomposites obtained by deposition. Furthermore, as the PF was increased from 50 Hz to 150 Hz, the content of TiN nanoparticles in Ni-W/TiN nanocomposites increased from 6.4 wt% to 9.6 wt% (Figure 7). As a result, the content of TiN nanoparticles incorporated in the nanocomposites increased as the PF increased [21,23]. Because of the higher pulse frequencies used in PCE deposition, the overpotentials of Ni²⁺ and W⁶⁺ ions increased in the plating solution, giving the metal ions more energy to adsorb TiN nanoparticles. Hence, abundant TiN nanoparticles were migrated to the cathode and increased their content in Ni-W/TiN nanocomposites. Lower PF, on the other hand, limited the capability of metal ions to adsorb TiN nanoparticles and resulted in a small quantity of TiN in co-deposited nanocomposites with Ni²⁺ and W⁶⁺ ions.

3.3. XRD Analysis

The XRD patterns of as-deposited Ni-W/TiN nanocomposites synthesized under various DCs and PFs are shown in Figure 8 and Figure 9. The amount of Co and Ni ions in the bath was 4–15 times greater than TiN nanoparticles, resulting in exceptionally low mass percentages of embedded TiN nanoparticles in the nanocomposites. As a result, the TiN phase exhibited weak diffraction intensities (Figure 8 and Figure 9). Moreover, solid solutions of NiW were generated as a result of Ni²⁺ and W⁶⁺ ions, which matched the XRD patterns. Furthermore, as the PF and DC were increased, the diffraction intensities of Ni-W/TiN nanocomposites decreased, leading to the finer Ni and W grains in the nanocomposites. As previously stated, a low DC and high PF generated by the pulsed power supply improved the quantities of implanted TiN nanoparticles, resulting in a large number of electro-crystalizing nucleation sites. This would refine grain size and restrict matrix grain growth during PCE.

3.4. Measurements of Microhardness

The influence of DC on the microhardness of Ni-W/TiN nanocomposites synthesized at a fixed PF of 150 Hz is shown in Figure 10. The DC had a significant impact on the microhardness of Ni-W/TiN nanocomposites. Compared with the coatings deposited at 30% and 50% DCs, the Ni-W/TiN nanocomposites prepared under the conditions of DC of 10% and 150 Hz PF had the maximum microhardness (914.5 HV). Figure 11 depicts the effect of PF on the microhardness of Ni-W/TiN nanocomposites deposited at 10% of fixed DC. The microhardness of Ni-W/TiN nanocomposites was significantly affected by the PF. The Ni-W/TiN nanocomposites deposited at 150 Hz and a DC of 10% had a mean microhardness value of 934.3 HV, which was higher than the mean microhardness of the other two nanocomposites. The hardness of ceramic particles and matrix grains embedded in the coating, as documented in the literature [25,26], greatly influences the microhardness of nanocomposites. Further, in the case of the same matrix metal grains, the higher content of ceramic particles in the coatings, the greater the microhardness should be. Therefore, the prepared Ni-W/TiN nanocomposites showed the highest microhardness at 10% DC and 150 Hz PF.

3.5. Wear Measurement

3.5.1. Weight Loss

The DC effect on the weight loss of a fixed pulse of 150 Hz generated Ni-W/TiN nanocomposites is shown in Figure 12. Throughout the wear test period, the weight loss of all three deposited nanocomposites decreased marginally when the DC was reduced. The weight loss of Ni-W/TiN nanocomposites synthesized at a DC of 50% was found to be the greatest—i.e., 34.7 mg. The weight loss of Ni-W/TiN nanocomposites deposited under a 10% DC, on the other hand, was only 16.6 mg, indicating their remarkable wear resistance. The PF effect on the weight loss of Ni-W/TiN nanocomposites synthesized when the DC was set to 10% is shown in Figure 13. A gradual decrease was observed in the weight loss of all three nanocomposites as the PF increased. When the PF was 50 Hz, the weight loss of prepared Ni-W/TiN nanocomposites was shown to be 32.5 mg, which was the maximum. The weight loss of the Ni-W/TiN nanocomposite deposited at 150 Hz, on the other hand, was just 17.1 mg, indicating excellent wear resistance.

3.5.2. Worn Surface Morphology

The worn surface morphology of Ni-W/TiN nanocomposites formed under varied DCs and PF was examined, as illustrated in Figure 14 and Figure 15. On the Ni-W/TiN nanocomposite surface deposited at 10% DC, some abrasion grooves with lesser depth and width were visible (Figure 14a). With the DC increment from 10% to 50% (Figure 14b,c), the abrasion grooves on the coating became larger and deeper, resulting in a large amount of wear weight loss, which was consistent with the results of weight loss. The Ni-W/TiN nanocomposites synthesized at 50 Hz and 100 Hz had a significant weight loss and more substantial surface defects, as shown in Figure 15. Meanwhile, the surface of Ni-W/TiN nanocomposites manufactured at 150 Hz had only a few slight scratches. Therefore, various factors contributed to the wear of Ni-W/TiN nanocomposites. First, the amount of TiN in the coatings had a significant impact on the wear resistance of Ni-W/TiN nanocomposites [27]. Dense TiN nanoparticles were incorporated into the metal matrix in Ni-W/TiN nanocomposites, resulting in nanocomposites with robust and stable structure. Thus, Ni-W/TiN nanocomposites prepared at 10% DC and 150 Hz PF showed outstanding wear resistance. Second, a significant number of TiN nanoparticles would be detached from the metal matrix when the content of TiN nanoparticles incorporated in the nanocomposites was higher, and a considerable number of rolling grains would be created during the wear test. This is normal because the coatings showed significant wear resistance. After all, a high content of high-hardness TiN nanoparticles successfully inhibited the formation of abrasive grooves [28]. Moreover, the wear rate of Ni-W/TiN nanocomposites is also influenced by the microhardness of nanocomposites and the spacing of the TiN particles [20].

3.6. TEM, In-Plane and Cross-Section Microstructures

As shown in Figure 16, the TEM and cross-section pictures of as-deposited Ni-W/TiN nanocomposites fabricated at 10% DC and 150 Hz PF were viewed. In Ni-W/TiN nanocomposites, there were several TiN nanoparticles embedded in metal grains. The TiN nanoparticles were homogeneously distributed in the nanocomposite with ~39.8 μm of an average thickness.

3.7. Corrosion Testing

The Bode and Nyquist plots of Ni-W/TiN nanocomposites synthesized under various DCs and pulse frequencies are shown individually in Figure 17 and Figure 18. With a DC of 10% and a PF of 150 Hz, the Ni-W/TiN nanocomposites had the highest impedance among all the six nanocomposites, indicating that their corrosion resistance was the best. Meanwhile, with the increase in DC and reduction in PF, the corrosion resistance of the nanocomposite presented a significant decrease. Therefore, appropriate electroplating parameters, such as PF and DC, were conducive to the development of uniform, dense, and fine structures, which could inhibit NaCl corrosive solution penetration into the bulk of Ni-W/TiN nanocomposite and could provide excellent corrosion resistance to the coating. However, the microstructures of Ni-W/TiN nanocomposites had coarse, inhomogeneous, and loose grains, easily keeping NaCl solution on the coating surface, thus accelerating the process of electrochemical reaction between the metal grains and NaCl liquid, which eventually led to the poor corrosion resistance of the nanocomposites.

4. Conclusions

On the deposited Ni-W/TiN nanocomposites, abundant tiny grains were present at a DC of 10%, resulting in a smooth, uniform, and fine microstructure. When the DC was 50%, the grain sizes of deposited Ni-W/TiN nanocomposites were the largest. With the increase in DC from 10% to 50%, the TiN nanoparticles content in Ni-W/TiN nanocomposites reduced from 11.3 wt% to 7.3 wt%. When the PF was increased from 50 Hz to 150 Hz, the content of TiN nanoparticles was also increased from 6.4 wt% to 9.6 wt% in Ni-W/TiN nanocomposites. Prefabricated Ni-W/TiN nanocomposites with a PF of 150 Hz and a DC of 10% had a mean thickness of ~39.8 μm and average microhardness of 934.3 HV. The weight loss of Ni-W/TiN nanocomposite was only 17.2 mg when the PF was 150 Hz, indicating that it exhibited outstanding wear resistance. In addition, the greatest impedance was found in Ni-W/TiN nanocomposites made with a DC of 10% and a PF of 150 Hz, indicating the best corrosion resistance.