Influence of CuSO4 concentration on microstructures and properties of electroless deposited Ni/Cu-P coatings

Influence of CuSO4 concentration on microstructures and properties of electroless deposited Ni/Cu-P coatings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Influence of CuSO 4 concentration on microstructures and properties of electroless deposited Ni/Cu-P coatings Qiang Li, Qiang Zhang, Zhenghai Han, Jun Hu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7672725/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2026 Read the published version in Scientific Reports → Version 1 posted 14 You are reading this latest preprint version Abstract This study focuses on improving the performance of Ni-P coatings by introducing varying concentrations (0.1–0.3 g/L) into the Ni-P plating solution to deposit Ni/Cu-P coatings. The influence of CuSO 4 concentration on the microstructure, surface roughness, brightness, hardness, wear resistance, corrosion resistance, and magnetic behavior of the coatings was explored. The findings revealed that the SCU-0.15 coating, prepared with 0.15 g/L CuSO 4 , showed a finer and more compact microstructure. Diffraction peaks corresponding to copper were observed in the SCU-0.15, SCU-0.2, and SCU-0.3 coatings. The Cu content in the SCU-0.15 coating was measured at 1.28 wt%. Both the SCU-0.15 and SCU-0.3 coatings displayed compact and fine cross-sectional morphologies, with coating thicknesses of 68.7 µm and 68.2 µm, respectively. TEM measurements revealed that the average diameters of the Ni/Cu solid solution in the SCU-0.15 and SCU-0.3 coatings were approximately 34.6 nm and 63.9 nm, respectively. The SCU-0, SCU-0.1, and SCU-0.15 coatings displayed a broad, bun-shaped nickel diffraction peak at 2 θ = 45°, indicating that these coatings possessed an amorphous Ni-P structure. The hardness of the SCU-0 coating was approximately 447.6 HV, whereas the SCU-0.15 coating showed a significantly higher hardness of about 713.5 HV. The SCU-0.15 coating exhibited the lowest wear loss among all the prepared coatings, whereas the SCU-0 coating showed the highest wear loss during wear testing. The saturation magnetization ( M s ) of the coatings dropped from 443 to 284 emu/cc as the CuSO 4 concentration was raised from 0.1 to 0.3 g/L. Further, the SCU-0.15 coating demonstrated the highest corrosion potential and polarization resistance compared to the other coatings. Moreover, the SCU-0.15 coating had the lowest corrosion current density at 30.79 µA/cm 2 , indicating excellent corrosion resistance. Furthermore, it showed the largest arc radius in the impedance spectrum and the highest charge transfer resistance of 4678.4 Ω·cm 2 , further confirming its improved corrosion protection performance. Physical sciences/Chemistry Physical sciences/Engineering Physical sciences/Materials science Electroless plating Ni/Cu⁃P coating CuSO4 concentration Microstructure Wear resistance Corrosion resistance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction Electroless deposition (ED) is widely used in the machinery, agriculture, chemical, and aviation industries due to its simple operation, low cost, and high processing efficiency [ 1 – 3 ]. Ni-P coatings are commonly fabricated for surface modification of both metallic and non-metallic materials using the ED technique. For example, it was reported by Rabizadeh et al. [ 4 ] that Ni-P coatings could be deposited via ED and that the incorporation of SiO 2 nanoparticles enhanced the corrosion resistance of the coatings. Successful fabrication of Ni-P-Cu coatings was achieved in a study by Bhattacharyya et al. [ 5 ], in which their corrosion and thermal performance were also thoroughly investigated. Ma et al. [ 6 ] analyzed the influence of phosphorous acid concentration on the characteristics of Ni-P-PTFE coatings and found that these coatings exhibited low friction coefficients against steel. However, the relatively low hardness, corrosion, and wear resistance of the Ni-P coatings limit their practical applications [ 7 , 8 ]. To improve their performance, third elements such as Cu, W, Co, and Mo are often incorporated into Ni-P coatings [ 9 – 12 ]. Generally, Cu ions act as both stabilizers and catalysts during the electroless deposition process of the Ni/Cu-P coatings [ 13 ]. When acting as a stabilizer, Cu ions inhibit the deposition rate of Ni ions and improve the coating morphology. However, as a catalyst, they accelerate Ni deposition, leading to a deterioration in coating quality. Therefore, investigating the influence of CuSO 4 concentration on the microstructure and characteristics of the Ni-P coatings is essential. To utilize the stabilizing effect of CuSO 4 for achieving a fine and compact coating with increased wear and corrosion resistance, CuSO 4 was added to the electroless Ni-P plating solution at concentration values within the range extending from 0.1 to 0.3 g/L. The effects of CuSO 4 concentration on the structure, hardness, surface roughness, corrosion and wear resistance, and magnetic characteristics of the Ni/Cu-P coatings were systematically investigated. This study offers technical support for enhancing the hardness, corrosion, and wear resistance of the Ni-P coatings and presents a new approach for their application in agricultural, industrial, and petroleum fields. 2. Experiment 2.1 Materials and plating condition The Q235 steel substrates, with dimensions equal to 20 mm × 15 mm × 2 mm, were polished sequentially using 200#, 600#, 800#, and 1200# abrasive papers. After polishing, the substrates underwent degreasing, coarsening, sensitization, and activation treatments. The solution compositions and process parameters for each step are detailed in Table 1 . All reagents used in the experiment were of analytical grade. After each treatment step, the obtained specimens were thoroughly cleaned with deionized water and dried before ED. The resulting coatings were designated as SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3, corresponding to CuSO 4 concentrations of 0, 0.1, 0.15, 0.2, and 0.3 g/L, respectively. Table 1 Solution compositions and process parameters for fabricating Ni/Cu-P coatings. Operation process Solution composition Condition Degreasing NaOH 60 g/L Temperature: 80℃, Time: 10 min, pH = 8.5 Na 2 CO 3 50 g/L Na 3 PO 4 40 g/L Coarsing HF 80 mL/L Temperature: 25℃, Time: 5 min pH = 3.5 H 2 SO 4 80 mL/L Sensitization PdCl 2 0.4 g/L Temperature: 25℃, Time: 5 min pH = 4.0 38% HCl 10 mL/L Activation SnCl 2 30 g/L Temperature: 25℃, Time: 10 s pH = 4.8 35% HCl 40 mL/L Electroless deposition NiSO 4 ·6H 2 O 30 g/L Temperature: 80℃, Depositing time: 100 min pH = 6.0 Na 3 C 6 H 5 O 7 ·2H 2 O 10 g/L NaC 2 H 3 O 2 ·3H 2 O 15 g/L C 3 H 6 O 3 30 g/L NaH 2 PO 2 ·H 2 O 25 g/L CH 4 N 2 S 0.01 g/L CuSO 4 0, 0.1, 0.15, 0.2, 0.3 g/L 2.2 Characterization A JSM-3400 scanning electron microscope (SEM) was employed to examine the cross-sectional and surface morphologies of the obtained coatings. The elemental compositions of the coatings were analyzed using an INC250 energy-dispersive spectrometry (EDS) system. Furthermore, a JEM-2100F transmission electron microscopy (TEM) system was utilized to study the microstructure of the prepared coatings. The phase structures of the coatings were studied via an AL-Y3500 X-ray diffractometer (XRD) using Cu Kα radiation, a tube current equal to 300 mA, an accelerating voltage equaling 50 kV, a scan rate equal to 2°/min, a scan range extending from 20°–90°, and a scanning step size equal to 0.02°. The coating hardness was determined via a VMH-002V microhardness tester under a load equal to 1 N and a holding time equaling 15 s. Surface roughness ( Ra ) was evaluated with a TR300 surface roughness tester, and coating brightness was assessed using a YG47 gloss meter at an incident angle of 45°. Wear experiments were carried out utilizing an MM-200 abrasion testing machine. A GCr15 quenched steel ring with a Φ30 mm grinding specimen was loaded with a force of 20 N and rotated at 200 rpm. The specimen was weighed every 5 min using an electronic balance, and the mass loss before and after each interval was recorded as the wear amount. The total wear test duration was 30 min. Moreover, the magnetic properties of the SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings were evaluated using a vibrating sample magnetometer (VSM, Lakeshore-7304). The polarization curves and electrochemical impedance spectra of the coatings in a 15 wt% HNO 3 solution were measured using a CS350 electrochemical testing system. A conventional 3-electrode setup was employed, with a Pt electrode (10 mm × 10 mm) as the auxiliary electrode, the coated sample (7 mm × 7 mm test area) as the working electrode, and a saturated calomel electrode (SCE) as the reference electrode. The prepared specimen was then immersed within the test solution for 15 min before testing to stabilize the open-circuit potential. The polarization profile was obtained over a voltage range of ± 250 mV relative to the open-circuit potential, with a scan rate equal to 50 mV/min. 3. Results and discussion 3.1 Surface and cross-sectional morphologies The surface morphologies of the obtained coatings obtained at various CuSO 4 concentration values (0–0.3 g/L) are shown in Fig. 1 . All coatings displayed the typical nodular structure characteristic of Ni-P coatings, appearing dense and continuous. As illustrated in Fig. 1 a, the surface of the Ni-P coating without CuSO 4 displayed non-uniform nodular clusters with various sizes, resulting in a relatively coarse morphology. However, the SCU-0.15 coating exhibited a finer and more compact structure compared to the SCU-0 and SCU-0.1 coatings. Furthermore, with the increase in CuSO 4 concentration, the nodules in the SCU-0.15 coating became smaller and more uniform in size, as displayed in Fig. 1 c. The improvement in coating morphology was primarily attributed to the standard electrode potential of Cu 2+ , which allowed it to preferentially precipitate and adsorb onto the substrate surface. The precipitated Cu acted as nucleation sites for subsequent Ni deposition, leading to finer nodules in the coating [ 14 ]. Cu 2+ inhibited the rapid precipitation of Ni, promoting a more uniform and compact coating structure [ 15 ]. When the CuSO 4 concentration reached 0.2 g/L and 0.3 g/L, various pyramid-like structures appeared on the surfaces of the SCU-0.2 and SCU-0.3 coatings, respectively, and their density increased with rising CuSO 4 concentration (Figs. 1 d and 1 e). These changes in surface morphology indicate that the addition of a small amount of CuSO 4 to the electroless Ni-P plating solution can enhance the surface quality of the coating. In this context, CuSO 4 acted as a stabilizer during the deposition process of the Ni-P coatings. Pyramid-shaped structures started forming on the coating surface as the concentration value of CuSO 4 exceeded a certain value (i.e., 0.2 g/L). This led to an increase in the grain size of the Ni-P coatings [ 16 ]. These results indicate that at higher CuSO 4 concentrations (0.2 and 0.3 g/L), Cu 2+ ions acted as catalysts in the plating solution. The EDS spectra of the different coatings are presented in Fig. 2 , and their corresponding compositions are given in Table 2 . As anticipated, no Cu was detected in the SCU-0 coating. In the SCU-0.1 coating, the Cu content was also very low (0.31 wt%), resulting in a weak diffraction peak. This may be attributed to the low Cu 2+ concentration in the SCU-0.1 bath and the preferential precipitation of Cu 2+ ions, most of which were consumed during the initial stage of the ED process [ 17 ]. However, distinct diffraction peaks corresponding to Cu appeared in the SCU-0.15, SCU-0.2, and SCU-0.3 coatings when the CuSO 4 concentrations reached 0.15, 0.2, and 0.3 g/L. The Cu contents in these coatings were 1.28, 3.82, and 7.43 wt%, respectively. The contents of P and Ni in all coatings decreased with an increase in the concentration of CuSO 4 . The P content in each coating remained above 10 wt%, indicating the formation of high-phosphorus coatings. Table 2 Element compositions in different coatings (wt%). Sample Ni Cu P SCU−0 87.18 0 12.82 SCU−0.1 86.15 0.31 13.54 SCU−0.15 85.34 1.28 13.38 SCU−0.2 84.31 3.82 12.88 SCU−0.3 81.25 7.43 11.32 The cross-sectional morphologies of the SCU-0, SCU-0.15, and SCU-0.3 coatings are presented in Fig. 3 . The SCU-0 coating had a coarse and porous structure, with a thickness of approximately 67.9 µm. However, the SCU-0.15 and SCU-0.3 coatings exhibited compact and refined cross-sectional morphologies, with coating thicknesses of approximately 68.7 µm and 68.2 µm, respectively. The higher electrode potential of copper compared to nickel leads to the preferential precipitation of copper ions during the ED process, which provides various nucleation sites for the subsequent deposition of nickel grains [ 18 ]. Therefore, the SCU-0.15 and SCU-0.3 coatings demonstrated compact and fine structures, while the SCU-0 coating showed a coarse and loose structure due to the absence of Cu 2+ ions in the plating bath. 3.2 TEM structure The TEM microstructures of the SCU-0, SCU-0.15, and SCU-0.3 coatings are displayed in Fig. 4 . The SCU-0 coating had a coarse microstructure, with an average Ni grain diameter of approximately 89.5 nm. When an appropriate amount of CuSO 4 (0.15 g/L) was added to the plating bath, the coating structure became finer and denser, with the average diameter of the Ni/Cu solid solution measuring approximately 34.6 nm. However, the coating displayed a coarser structure as the CuSO 4 concentration was raised to 0.3 g/L, and the average size of the Ni/Cu solid solution increased to approximately 63.9 nm. These results were consistent with the SEM observations. Only Ni grains were observed in the Ni-P coating, as no Cu 2+ ions were added to the plating solution. However, Ni/Cu solid solutions were present in the SCU-0.15 and SCU-0.3 coatings due to the introduction of CuSO 4 into the plating bath. Since the concentration value of the Cu ions within the solution was relatively low, the XRD profiles of the prepared Ni/Cu-P coatings primarily showed nickel grain characteristics, as illustrated in the upper right corners of Figs. 4 b and 4 c. 3.3 Phase structure The XRD spectra of the SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings are provided in Fig. 5 . The SCU-0, SCU-0.1, and SCU-0.15 coatings displayed only a broad, bun-shaped nickel diffraction peak at 2 θ = 45°, indicating that these three coatings possessed amorphous Ni-P structures. The addition of a small amount of CuSO 4 did not alter the amorphous structure of the coating, which contributed to its excellent wear and corrosion resistance [ 19 , 20 ]. When the CuSO 4 concentration reached 0.2 and 0.3 g/L, characteristic diffraction peaks of the Cu element appeared at 2 θ = 43.4° and 50.3°, corresponding to the planar directions (111) and (200) of Cu₀.₈₁Ni₀.₁₉, respectively, indicating the formation of numerous Ni/Cu solid solutions in the SCU-0.2 and SCU-0.3 coatings [ 21 ]. Furthermore, the content of the Ni/Cu solid solution increased with the rising concentration of CuSO 4 in the plating bath. 3.4 Hardness Figure 6 illustrates the relationship between coating hardness and CuSO 4 concentration. The coating hardness increased with rising CuSO 4 concentration. At 0 g/L CuSO 4 , the hardness of the SCU-0 coating was approximately 447.6 HV. The hardness of the SCU-0.15 coating increased significantly to 713.5 HV when the concentration reached 0.15 g/L. At lower CuSO 4 concentrations, the initially deposited Cu served as nucleation sites for Ni grains, promoting grain refinement [ 22 ]. This led to a denser and more uniform coating structure, therefore enhancing the coating's hardness. As the CuSO 4 concentration further increased to 0.3 g/L, Ni and Cu were co-deposited to form a Ni/Cu solid solution, which effectively inhibited coating deformation and further increased hardness. Thus, the SCU-0.3 coating demonstrated the highest hardness of 728.9 HV among all samples. 3.5 Surface roughness and brightness The impact of the CuSO 4 concentration value on the surface roughness and brightness of the coatings is illustrated in Fig. 7 . The Ra values of SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings first decreased and then increased as the CuSO 4 concentration value was enhanced from 0 to 0.3 g/L. The SCU-0.15 coating revealed the lowest surface roughness of 0.78 µm at a CuSO 4 concentration value equal to 0.15 g/L, whereas the SCU-0 coating had the highest surface roughness of 1.23 µm among all samples. Moreover, the brightness of the coatings initially increased and then followed a decreasing trend with a rise in CuSO 4 concentration. The SCU-0.15 coating, deposited at 0.15 g/L CuSO 4 , indicated the highest brightness of 196.8 GU, indicating excellent surface quality. The addition of an appropriate concentration of CuSO 4 to the plating solution resulted in a fine and uniform coating structure, enhancing the surface brightness [ 23 ]. However, at CuSO 4 concentrations of 0.2 to 0.3 g/L, numerous Ni-Cu solid solutions formed on the coating surfaces, leading to the development of pyramid-like structures on SCU-0.2 and SCU-0.3 coatings, which resulted in decreased brightness. 3.6 Wear resistance The wear loss curves of SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings are shown in Fig. 8 . The wear losses of all coatings increased rapidly during the initial wear period from 0 to 15 min, which can be attributed to the time required to smooth the rough surfaces at the beginning of the test. From 15 to 30 min, the wear losses of all coatings continued to increase gradually with wear time. As the wear test progressed, the rough surface of the coating became smoother, resulting in full contact between the coating surface and the friction pair. Therefore, the wear resistance of the coating slowly increased [ 24 ]. Moreover, the SCU-0.15 coating indicated the lowest wear loss among all coatings, while the SCU-0 coating showed the highest wear loss during the wear test. This difference is attributed to the microstructure of the coatings, as a finer and more compact structure significantly enhances wear resistance [ 25 ]. The worn surface morphologies of various coatings after the wear test are shown in Fig. 9 . No pyramid-like structures were observed on the surfaces of the Ni-P and Ni/Cu-P coatings, as the rough surfaces were smoothed during the wear experiment. The SCU-0 coating (Fig. 9 a) revealed deep and wide furrows, resulting from plastic deformation during friction testing. Material buildup occurred along the edges of the wear tracks [ 26 ]. However, the depth and width of the furrows decreased as the concentration of CuSO 4 concentration was raised up to 0.15 g/L (Fig. 9 c), indicating the excellent wear resistance of the SCU-0.15 coating. As previously mentioned, the microstructure played a pivotal role in the wear resistance of the coating. The SCU-0.15 coating revealed a fine and compact microstructure, which enhanced its wear resistance, resulting in minimal wear loss and shallower furrows. Various bumps appeared on the surface of the SCU-0.3 coating, corresponding to Ni/Cu solid solutions (Fig. 9 e). This occurred because the Ni metal in the coating was worn away, exposing the Ni/Cu solid solutions on the surface. 3.7 Magnetic property The coercivity ( H c ) and saturation magnetization ( M s ) profiles of the Ni-P and Ni/Cu-P coatings are presented in Fig. 10 . All coatings showed low H c values, indicating soft magnetic behavior. Among them, the SCU-0 coating displayed the highest M s value of 802 emu/cc. The M s value of the coating dropped from 443 to 284 emu/cc as the CuSO 4 concentration was raised from 0 to 0.3 g/L. This trend can be attributed to the fact that copper is a non-magnetic element with negligible M s , whereas nickel is ferromagnetic with a high M s [ 27 ]. Therefore, increasing Cu content in the coating resulted in a gradual reduction in its overall M s . To explore the impact of CuSO 4 concentration on the magnetic properties of the coatings further, their Cu contents were analyzed using the Lakeshore-7304 vibrating sample magnetometer. The influence of CuSO 4 concentration on the M s of the coatings is presented in Fig. 11 . It was observed that the M s value decreased from approximately 440 emu/cc to 285 emu/cc as the CuSO 4 concentration value was enhanced from 0.1 to 0.3 g/L, which aligns with the magnetization measurement results. 3.8 Corrosion resistance The impedance spectra and electrochemical polarization profiles of the coatings in 15 wt% HNO 3 solution are shown in Fig. 12 , while their corresponding corrosion current density ( J corr ), corrosion potential ( E corr ), polarization resistance ( R p ), and charge transfer resistance ( R ct ) values are provided in Table 3 . The corrosion potential and polarization resistance of the coatings initially increased and then followed a decreasing trend as the CuSO 4 concentration was increased, while the corrosion current density showed the opposite trend, first decreasing and then rising. The SCU-0.15 coating displayed the highest corrosion potential ( E corr = − 0.002 V) and polarization resistance ( R p = 1190.3 Ω·cm 2 ) among all samples. Moreover, the corrosion current density of the SCU-0.15 coating was the lowest at 30.79 µA/cm², indicating its higher corrosion resistance. This outstanding performance is attributed to the coating’s dense and homogeneous amorphous structure formed at a CuSO 4 concentration of 0.15 g/L, which lacks grain boundaries, enhancing its corrosion resistance [ 27 , 28 ]. Similarly, the corrosion potentials and polarization resistances of the SCU-0.2 and SCU-0.3 coatings were lower, while their corrosion current densities were higher than those of the SCU-0 coating, indicating poorer corrosion resistance. This decline is attributed to the co-deposition of Ni and Cu at CuSO 4 concentrations of 0.2 and 0.3 g/L, which transformed the coating structure from amorphous to a mixed crystalline phase. Therefore, various corrosive microcells formed at the grain boundaries of the microcrystalline structure, accelerating the corrosion process [ 29 ]. Table 3 Electrochemical parameters of different coatings. Sample E corr (V) J corr (µA/cm 2 ) R p (Ω·cm 2 ) R ct (Ω·cm 2 ) SCU−0 −0.153 33.02 746.1 4381.8 SCU−0.1 −0.086 31.61 952.2 4531.9 SCU−0.15 −0.002 30.79 1190.3 4678.4 SCU−0.2 −0.237 34.05 684.6 4316.7 SCU−0.3 −0.291 34.18 663.4 4251.5 Figure 13 shows the electrochemical impedance spectra of the different coatings in 15 wt% HNO 3 solution. All spectra showed similar semicircular shapes, indicating that the corrosion process involves a single time constant. The SCU-0.15 coating indicated the largest arc radius in the impedance spectrum, corresponding to the highest charge transfer resistance of 4678.4 Ω·cm 2 . However, the SCU-0.3 coating showed the smallest arc radius, with a charge transfer resistance of 4251.5 Ω·cm 2 . The results also confirmed that the SCU-0.15 coating exhibited the best corrosion resistance, while the SCU-0.3 coating showed the poorest corrosion resistance [ 30 ]. 4. Conclusions (1) The SCU-0.15 coating exhibited a finer and more compact structure compared to the SCU-0 and SCU-0.1 coatings. Furthermore, with the increase in CuSO 4 concentration, the nodules in the SCU-0.15 coating became smaller and more uniform in size. Furthermore, distinct diffraction peaks corresponding to Cu appeared in the SCU-0.15, SCU-0.2, and SCU-0.3 coatings when the CuSO 4 concentrations reached 0.15, 0.2, and 0.3 g/L. The Cu contents in these coatings were 1.28, 3.82, and 7.43 wt%, respectively. (2) The SCU-0.15 and SCU-0.3 coatings exhibited compact and refined cross-sectional morphologies, with coating thicknesses of approximately 68.7 μm and 68.2 μm, respectively. When an appropriate amount of CuSO 4 (0.15 g/L) was added to the plating bath, the coating structure became finer and denser, with the average diameter of the Ni/Cu solid solution measuring approximately 34.6 nm. However, the coating displayed a coarser structure as the CuSO 4 concentration was raised to 0.3 g/L, and the average size of the Ni/Cu solid solution increased to approximately 63.9 nm. (3) The SCU-0, SCU-0.1, and SCU-0.15 coatings displayed only a broad, bun-shaped nickel diffraction peak at 2 θ = 45°, indicating that these three coatings possessed amorphous Ni-P structures. When the CuSO 4 concentration reached 0.2 and 0.3 g/L, characteristic diffraction peaks of the Cu element appeared at 2 θ = 43.4° and 50.3°, corresponding to the planar directions (111) and (200) of Cu₀.₈₁Ni₀.₁₉, respectively, indicating the formation of numerous Ni/Cu solid solutions in the SCU-0.2 and SCU-0.3 coatings. (4) The SCU-0.15 coating indicated the lowest wear loss among all coatings, while the SCU-0 coating showed the highest wear loss during the wear test. The M s value of the coating dropped from 443 to 284 emu/cc as the CuSO 4 concentration was raised from 0 to 0.3 g/L. The SCU-0.15 coating indicated the largest arc radius in the impedance spectrum, corresponding to the highest charge transfer resistance of 4678.4 Ω·cm 2 . However, the SCU-0.3 coating showed the smallest arc radius, with a charge transfer resistance of 4251.5 Ω·cm 2 . Declarations Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution Qiang Liand Qiang Zhang wrote the main manuscript text, Zhenghai Han and Jun Hu prepared figures 1-13. All authors reviewed the manuscript. 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coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/d981359bec9a7735489d2593.png"},{"id":93117509,"identity":"3606501b-d1f6-4b71-8cc6-e8f9d16d0b4d","added_by":"auto","created_at":"2025-10-09 09:00:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":548404,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCross-sectional morphologies of (a) SCU-0, (b) SCU-0.15, and (c) SCU-0.3 coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/05bb14fa3e0ef4bcee80a9c8.png"},{"id":93118057,"identity":"9dbfe2f4-7383-4c13-b7ce-3bcb42f22f53","added_by":"auto","created_at":"2025-10-09 09:08:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":473852,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTEM images of (a) SCU-0, (b) SCU-0.15, and (c) SCU-0.3 coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/b90535f53b4f5e21b0618c78.png"},{"id":93118055,"identity":"bda7dc0c-0bf5-43c6-a478-7cad9d444d38","added_by":"auto","created_at":"2025-10-09 09:08:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":77140,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXRD spectra of different coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/e6231d38ea622f9e9db85e9f.png"},{"id":93117517,"identity":"ca9aaf8e-a61a-4cb0-b2cb-0b38cf799ed1","added_by":"auto","created_at":"2025-10-09 09:00:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":47647,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of CuSO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e concentration on hardness of coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/7ebc1370a8b240f20b89aee0.png"},{"id":93117511,"identity":"0b3d0402-4d65-495c-a4ca-f53bbec682e4","added_by":"auto","created_at":"2025-10-09 09:00:00","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":106772,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of CuSO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e concentration on roughness and brightness of coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/5beb3635101606b8a2cc394d.png"},{"id":93117539,"identity":"af660980-5e74-458e-9985-c122ce25dcfb","added_by":"auto","created_at":"2025-10-09 09:00:02","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":95292,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eWear loss curves of different coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/53afa0c0870fbb4a29bfe78b.png"},{"id":93118062,"identity":"84a14fb7-2f8c-471e-8514-ac3a79e8bb46","added_by":"auto","created_at":"2025-10-09 09:08:00","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":522706,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eWorn SEM images of (a) SCU-0, (b) SCU-0.1, (c) SCU-0.15, (d) SCU-0.2, and (e) SCU-0.3 coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/12697aecf32776807750dc8c.png"},{"id":93118069,"identity":"f9a99381-09be-431a-8c41-54b221f869be","added_by":"auto","created_at":"2025-10-09 09:08:02","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":106890,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMagnetic hysteresis curves of Ni-P and Ni/Cu-P coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/b828e2f308875835e10b7414.png"},{"id":93117519,"identity":"7044303b-c0c6-4656-aba4-7592c8c3731e","added_by":"auto","created_at":"2025-10-09 09:00:00","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":60668,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of CuSO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e concentration on saturation magnetization of coatings.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/6de7a6d5af02dc9362182b78.png"},{"id":93118060,"identity":"fabee405-15d2-4d5e-b4cf-e04d7d8c56f3","added_by":"auto","created_at":"2025-10-09 09:08:00","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":68231,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePolarization curves and electrochemical impedance spectra of different coatings in 15 wt% HNO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e solution.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/f86965c299891a0fd2c125ad.png"},{"id":93118067,"identity":"30e49fb6-9b30-41aa-80d8-f1f0eb696a21","added_by":"auto","created_at":"2025-10-09 09:08:01","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":84816,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical impedance spectra of different coatings in 15 wt% HNO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e solution.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/a5157d2bead1ee44b852a0ae.png"},{"id":104252200,"identity":"2c65f0e9-4e0e-4cbf-b590-fa0fcf4dccac","added_by":"auto","created_at":"2026-03-09 16:17:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4155435,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7672725/v1/e520f22b-978e-4304-8fca-0966c1da9415.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eInfluence of CuSO\u003csub\u003e4\u003c/sub\u003e concentration on microstructures and properties of electroless deposited Ni/Cu-P coatings\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eElectroless deposition (ED) is widely used in the machinery, agriculture, chemical, and aviation industries due to its simple operation, low cost, and high processing efficiency [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Ni-P coatings are commonly fabricated for surface modification of both metallic and non-metallic materials using the ED technique. For example, it was reported by Rabizadeh \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] that Ni-P coatings could be deposited via ED and that the incorporation of SiO\u003csub\u003e2\u003c/sub\u003e nanoparticles enhanced the corrosion resistance of the coatings. Successful fabrication of Ni-P-Cu coatings was achieved in a study by Bhattacharyya \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], in which their corrosion and thermal performance were also thoroughly investigated. Ma \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] analyzed the influence of phosphorous acid concentration on the characteristics of Ni-P-PTFE coatings and found that these coatings exhibited low friction coefficients against steel. However, the relatively low hardness, corrosion, and wear resistance of the Ni-P coatings limit their practical applications [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. To improve their performance, third elements such as Cu, W, Co, and Mo are often incorporated into Ni-P coatings [\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eGenerally, Cu ions act as both stabilizers and catalysts during the electroless deposition process of the Ni/Cu-P coatings [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. When acting as a stabilizer, Cu ions inhibit the deposition rate of Ni ions and improve the coating morphology. However, as a catalyst, they accelerate Ni deposition, leading to a deterioration in coating quality. Therefore, investigating the influence of CuSO\u003csub\u003e4\u003c/sub\u003e concentration on the microstructure and characteristics of the Ni-P coatings is essential. To utilize the stabilizing effect of CuSO\u003csub\u003e4\u003c/sub\u003e for achieving a fine and compact coating with increased wear and corrosion resistance, CuSO\u003csub\u003e4\u003c/sub\u003e was added to the electroless Ni-P plating solution at concentration values within the range extending from 0.1 to 0.3 g/L. The effects of CuSO\u003csub\u003e4\u003c/sub\u003e concentration on the structure, hardness, surface roughness, corrosion and wear resistance, and magnetic characteristics of the Ni/Cu-P coatings were systematically investigated. This study offers technical support for enhancing the hardness, corrosion, and wear resistance of the Ni-P coatings and presents a new approach for their application in agricultural, industrial, and petroleum fields.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials and plating condition\u003c/h2\u003e\u003cp\u003eThe Q235 steel substrates, with dimensions equal to 20 mm \u0026times; 15 mm \u0026times; 2 mm, were polished sequentially using 200#, 600#, 800#, and 1200# abrasive papers. After polishing, the substrates underwent degreasing, coarsening, sensitization, and activation treatments. The solution compositions and process parameters for each step are detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. All reagents used in the experiment were of analytical grade. After each treatment step, the obtained specimens were thoroughly cleaned with deionized water and dried before ED. The resulting coatings were designated as SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3, corresponding to CuSO\u003csub\u003e4\u003c/sub\u003e concentrations of 0, 0.1, 0.15, 0.2, and 0.3 g/L, respectively.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSolution compositions and process parameters for fabricating Ni/Cu-P coatings.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOperation process\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eSolution composition\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCondition\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eDegreasing\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaOH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e60 g/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eTemperature: 80℃,\u003c/p\u003e\u003cp\u003eTime: 10 min,\u003c/p\u003e\u003cp\u003epH\u0026thinsp;=\u0026thinsp;8.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e50 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNa\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e40 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCoarsing\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHF\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e80 mL/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTemperature: 25℃,\u003c/p\u003e\u003cp\u003eTime: 5 min\u003c/p\u003e\u003cp\u003epH\u0026thinsp;=\u0026thinsp;3.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e80 mL/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSensitization\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePdCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.4 g/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTemperature: 25℃,\u003c/p\u003e\u003cp\u003eTime: 5 min\u003c/p\u003e\u003cp\u003epH\u0026thinsp;=\u0026thinsp;4.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e38% HCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10 mL/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eActivation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSnCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e30 g/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTemperature: 25℃,\u003c/p\u003e\u003cp\u003eTime: 10 s\u003c/p\u003e\u003cp\u003epH\u0026thinsp;=\u0026thinsp;4.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35% HCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e40 mL/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"6\" rowspan=\"7\"\u003e\u003cp\u003eElectroless deposition\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNiSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e30 g/L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"6\" rowspan=\"7\"\u003e\u003cp\u003eTemperature: 80℃,\u003c/p\u003e\u003cp\u003eDepositing time: 100 min\u003c/p\u003e\u003cp\u003epH\u0026thinsp;=\u0026thinsp;6.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNa\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaC\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eC\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e30 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCH\u003csub\u003e4\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.01 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCuSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0, 0.1, 0.15, 0.2, 0.3 g/L\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Characterization\u003c/h2\u003e\u003cp\u003eA JSM-3400 scanning electron microscope (SEM) was employed to examine the cross-sectional and surface morphologies of the obtained coatings. The elemental compositions of the coatings were analyzed using an INC250 energy-dispersive spectrometry (EDS) system. Furthermore, a JEM-2100F transmission electron microscopy (TEM) system was utilized to study the microstructure of the prepared coatings. The phase structures of the coatings were studied via an AL-Y3500 X-ray diffractometer (XRD) using Cu Kα radiation, a tube current equal to 300 mA, an accelerating voltage equaling 50 kV, a scan rate equal to 2\u0026deg;/min, a scan range extending from 20\u0026deg;\u0026ndash;90\u0026deg;, and a scanning step size equal to 0.02\u0026deg;. The coating hardness was determined via a VMH-002V microhardness tester under a load equal to 1 N and a holding time equaling 15 s. Surface roughness (\u003cem\u003eRa\u003c/em\u003e) was evaluated with a TR300 surface roughness tester, and coating brightness was assessed using a YG47 gloss meter at an incident angle of 45\u0026deg;.\u003c/p\u003e\u003cp\u003eWear experiments were carried out utilizing an MM-200 abrasion testing machine. A GCr15 quenched steel ring with a Φ30 mm grinding specimen was loaded with a force of 20 N and rotated at 200 rpm. The specimen was weighed every 5 min using an electronic balance, and the mass loss before and after each interval was recorded as the wear amount. The total wear test duration was 30 min. Moreover, the magnetic properties of the SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings were evaluated using a vibrating sample magnetometer (VSM, Lakeshore-7304).\u003c/p\u003e\u003cp\u003eThe polarization curves and electrochemical impedance spectra of the coatings in a 15 wt% HNO\u003csub\u003e3\u003c/sub\u003e solution were measured using a CS350 electrochemical testing system. A conventional 3-electrode setup was employed, with a Pt electrode (10 mm \u0026times; 10 mm) as the auxiliary electrode, the coated sample (7 mm \u0026times; 7 mm test area) as the working electrode, and a saturated calomel electrode (SCE) as the reference electrode. The prepared specimen was then immersed within the test solution for 15 min before testing to stabilize the open-circuit potential. The polarization profile was obtained over a voltage range of \u0026plusmn;\u0026thinsp;250 mV relative to the open-circuit potential, with a scan rate equal to 50 mV/min.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Surface and cross-sectional morphologies\u003c/h2\u003e\u003cp\u003eThe surface morphologies of the obtained coatings obtained at various CuSO\u003csub\u003e4\u003c/sub\u003e concentration values (0\u0026ndash;0.3 g/L) are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. All coatings displayed the typical nodular structure characteristic of Ni-P coatings, appearing dense and continuous. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the surface of the Ni-P coating without CuSO\u003csub\u003e4\u003c/sub\u003e displayed non-uniform nodular clusters with various sizes, resulting in a relatively coarse morphology. However, the SCU-0.15 coating exhibited a finer and more compact structure compared to the SCU-0 and SCU-0.1 coatings. Furthermore, with the increase in CuSO\u003csub\u003e4\u003c/sub\u003e concentration, the nodules in the SCU-0.15 coating became smaller and more uniform in size, as displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. The improvement in coating morphology was primarily attributed to the standard electrode potential of Cu\u003csup\u003e2+\u003c/sup\u003e, which allowed it to preferentially precipitate and adsorb onto the substrate surface. The precipitated Cu acted as nucleation sites for subsequent Ni deposition, leading to finer nodules in the coating [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Cu\u003csup\u003e2+\u003c/sup\u003e inhibited the rapid precipitation of Ni, promoting a more uniform and compact coating structure [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. When the CuSO\u003csub\u003e4\u003c/sub\u003e concentration reached 0.2 g/L and 0.3 g/L, various pyramid-like structures appeared on the surfaces of the SCU-0.2 and SCU-0.3 coatings, respectively, and their density increased with rising CuSO\u003csub\u003e4\u003c/sub\u003e concentration (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). These changes in surface morphology indicate that the addition of a small amount of CuSO\u003csub\u003e4\u003c/sub\u003e to the electroless Ni-P plating solution can enhance the surface quality of the coating. In this context, CuSO\u003csub\u003e4\u003c/sub\u003e acted as a stabilizer during the deposition process of the Ni-P coatings. Pyramid-shaped structures started forming on the coating surface as the concentration value of CuSO\u003csub\u003e4\u003c/sub\u003e exceeded a certain value (i.e., 0.2 g/L). This led to an increase in the grain size of the Ni-P coatings [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. These results indicate that at higher CuSO\u003csub\u003e4\u003c/sub\u003e concentrations (0.2 and 0.3 g/L), Cu\u003csup\u003e2+\u003c/sup\u003e ions acted as catalysts in the plating solution.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe EDS spectra of the different coatings are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, and their corresponding compositions are given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. As anticipated, no Cu was detected in the SCU-0 coating. In the SCU-0.1 coating, the Cu content was also very low (0.31 wt%), resulting in a weak diffraction peak. This may be attributed to the low Cu\u003csup\u003e2+\u003c/sup\u003e concentration in the SCU-0.1 bath and the preferential precipitation of Cu\u003csup\u003e2+\u003c/sup\u003e ions, most of which were consumed during the initial stage of the ED process [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, distinct diffraction peaks corresponding to Cu appeared in the SCU-0.15, SCU-0.2, and SCU-0.3 coatings when the CuSO\u003csub\u003e4\u003c/sub\u003e concentrations reached 0.15, 0.2, and 0.3 g/L. The Cu contents in these coatings were 1.28, 3.82, and 7.43 wt%, respectively. The contents of P and Ni in all coatings decreased with an increase in the concentration of CuSO\u003csub\u003e4\u003c/sub\u003e. The P content in each coating remained above 10 wt%, indicating the formation of high-phosphorus coatings.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eElement compositions in different coatings (wt%).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eP\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e87.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e12.82\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e86.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e13.54\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e85.34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e13.38\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e84.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.82\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e12.88\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e81.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e11.32\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe cross-sectional morphologies of the SCU-0, SCU-0.15, and SCU-0.3 coatings are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The SCU-0 coating had a coarse and porous structure, with a thickness of approximately 67.9 \u0026micro;m. However, the SCU-0.15 and SCU-0.3 coatings exhibited compact and refined cross-sectional morphologies, with coating thicknesses of approximately 68.7 \u0026micro;m and 68.2 \u0026micro;m, respectively. The higher electrode potential of copper compared to nickel leads to the preferential precipitation of copper ions during the ED process, which provides various nucleation sites for the subsequent deposition of nickel grains [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Therefore, the SCU-0.15 and SCU-0.3 coatings demonstrated compact and fine structures, while the SCU-0 coating showed a coarse and loose structure due to the absence of Cu\u003csup\u003e2+\u003c/sup\u003e ions in the plating bath.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.2 TEM structure\u003c/h2\u003e\u003cp\u003eThe TEM microstructures of the SCU-0, SCU-0.15, and SCU-0.3 coatings are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The SCU-0 coating had a coarse microstructure, with an average Ni grain diameter of approximately 89.5 nm. When an appropriate amount of CuSO\u003csub\u003e4\u003c/sub\u003e (0.15 g/L) was added to the plating bath, the coating structure became finer and denser, with the average diameter of the Ni/Cu solid solution measuring approximately 34.6 nm. However, the coating displayed a coarser structure as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration was raised to 0.3 g/L, and the average size of the Ni/Cu solid solution increased to approximately 63.9 nm. These results were consistent with the SEM observations.\u003c/p\u003e\u003cp\u003eOnly Ni grains were observed in the Ni-P coating, as no Cu\u003csup\u003e2+\u003c/sup\u003e ions were added to the plating solution. However, Ni/Cu solid solutions were present in the SCU-0.15 and SCU-0.3 coatings due to the introduction of CuSO\u003csub\u003e4\u003c/sub\u003e into the plating bath. Since the concentration value of the Cu ions within the solution was relatively low, the XRD profiles of the prepared Ni/Cu-P coatings primarily showed nickel grain characteristics, as illustrated in the upper right corners of Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Phase structure\u003c/h2\u003e\u003cp\u003eThe XRD spectra of the SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings are provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The SCU-0, SCU-0.1, and SCU-0.15 coatings displayed only a broad, bun-shaped nickel diffraction peak at 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45\u0026deg;, indicating that these three coatings possessed amorphous Ni-P structures. The addition of a small amount of CuSO\u003csub\u003e4\u003c/sub\u003e did not alter the amorphous structure of the coating, which contributed to its excellent wear and corrosion resistance [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. When the CuSO\u003csub\u003e4\u003c/sub\u003e concentration reached 0.2 and 0.3 g/L, characteristic diffraction peaks of the Cu element appeared at 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;43.4\u0026deg; and 50.3\u0026deg;, corresponding to the planar directions (111) and (200) of Cu₀.₈₁Ni₀.₁₉, respectively, indicating the formation of numerous Ni/Cu solid solutions in the SCU-0.2 and SCU-0.3 coatings [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Furthermore, the content of the Ni/Cu solid solution increased with the rising concentration of CuSO\u003csub\u003e4\u003c/sub\u003e in the plating bath.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Hardness\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e illustrates the relationship between coating hardness and CuSO\u003csub\u003e4\u003c/sub\u003e concentration. The coating hardness increased with rising CuSO\u003csub\u003e4\u003c/sub\u003e concentration. At 0 g/L CuSO\u003csub\u003e4\u003c/sub\u003e, the hardness of the SCU-0 coating was approximately 447.6 HV. The hardness of the SCU-0.15 coating increased significantly to 713.5 HV when the concentration reached 0.15 g/L. At lower CuSO\u003csub\u003e4\u003c/sub\u003e concentrations, the initially deposited Cu served as nucleation sites for Ni grains, promoting grain refinement [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This led to a denser and more uniform coating structure, therefore enhancing the coating's hardness. As the CuSO\u003csub\u003e4\u003c/sub\u003e concentration further increased to 0.3 g/L, Ni and Cu were co-deposited to form a Ni/Cu solid solution, which effectively inhibited coating deformation and further increased hardness. Thus, the SCU-0.3 coating demonstrated the highest hardness of 728.9 HV among all samples.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Surface roughness and brightness\u003c/h2\u003e\u003cp\u003eThe impact of the CuSO\u003csub\u003e4\u003c/sub\u003e concentration value on the surface roughness and brightness of the coatings is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The \u003cem\u003eRa\u003c/em\u003e values of SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings first decreased and then increased as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration value was enhanced from 0 to 0.3 g/L. The SCU-0.15 coating revealed the lowest surface roughness of 0.78 \u0026micro;m at a CuSO\u003csub\u003e4\u003c/sub\u003e concentration value equal to 0.15 g/L, whereas the SCU-0 coating had the highest surface roughness of 1.23 \u0026micro;m among all samples. Moreover, the brightness of the coatings initially increased and then followed a decreasing trend with a rise in CuSO\u003csub\u003e4\u003c/sub\u003e concentration. The SCU-0.15 coating, deposited at 0.15 g/L CuSO\u003csub\u003e4\u003c/sub\u003e, indicated the highest brightness of 196.8 GU, indicating excellent surface quality. The addition of an appropriate concentration of CuSO\u003csub\u003e4\u003c/sub\u003e to the plating solution resulted in a fine and uniform coating structure, enhancing the surface brightness [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. However, at CuSO\u003csub\u003e4\u003c/sub\u003e concentrations of 0.2 to 0.3 g/L, numerous Ni-Cu solid solutions formed on the coating surfaces, leading to the development of pyramid-like structures on SCU-0.2 and SCU-0.3 coatings, which resulted in decreased brightness.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.6 Wear resistance\u003c/h2\u003e\u003cp\u003eThe wear loss curves of SCU-0, SCU-0.1, SCU-0.15, SCU-0.2, and SCU-0.3 coatings are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The wear losses of all coatings increased rapidly during the initial wear period from 0 to 15 min, which can be attributed to the time required to smooth the rough surfaces at the beginning of the test. From 15 to 30 min, the wear losses of all coatings continued to increase gradually with wear time. As the wear test progressed, the rough surface of the coating became smoother, resulting in full contact between the coating surface and the friction pair. Therefore, the wear resistance of the coating slowly increased [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Moreover, the SCU-0.15 coating indicated the lowest wear loss among all coatings, while the SCU-0 coating showed the highest wear loss during the wear test. This difference is attributed to the microstructure of the coatings, as a finer and more compact structure significantly enhances wear resistance [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe worn surface morphologies of various coatings after the wear test are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. No pyramid-like structures were observed on the surfaces of the Ni-P and Ni/Cu-P coatings, as the rough surfaces were smoothed during the wear experiment. The SCU-0 coating (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea) revealed deep and wide furrows, resulting from plastic deformation during friction testing. Material buildup occurred along the edges of the wear tracks [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. However, the depth and width of the furrows decreased as the concentration of CuSO\u003csub\u003e4\u003c/sub\u003e concentration was raised up to 0.15 g/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec), indicating the excellent wear resistance of the SCU-0.15 coating. As previously mentioned, the microstructure played a pivotal role in the wear resistance of the coating. The SCU-0.15 coating revealed a fine and compact microstructure, which enhanced its wear resistance, resulting in minimal wear loss and shallower furrows. Various bumps appeared on the surface of the SCU-0.3 coating, corresponding to Ni/Cu solid solutions (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ee). This occurred because the Ni metal in the coating was worn away, exposing the Ni/Cu solid solutions on the surface.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.7 Magnetic property\u003c/h2\u003e\u003cp\u003eThe coercivity (\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e) and saturation magnetization (\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e) profiles of the Ni-P and Ni/Cu-P coatings are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. All coatings showed low \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e values, indicating soft magnetic behavior. Among them, the SCU-0 coating displayed the highest \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e value of 802 emu/cc. The \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e value of the coating dropped from 443 to 284 emu/cc as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration was raised from 0 to 0.3 g/L. This trend can be attributed to the fact that copper is a non-magnetic element with negligible \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e, whereas nickel is ferromagnetic with a high \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Therefore, increasing Cu content in the coating resulted in a gradual reduction in its overall \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eTo explore the impact of CuSO\u003csub\u003e4\u003c/sub\u003e concentration on the magnetic properties of the coatings further, their Cu contents were analyzed using the Lakeshore-7304 vibrating sample magnetometer. The influence of CuSO\u003csub\u003e4\u003c/sub\u003e concentration on the \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e of the coatings is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. It was observed that the \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e value decreased from approximately 440 emu/cc to 285 emu/cc as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration value was enhanced from 0.1 to 0.3 g/L, which aligns with the magnetization measurement results.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.8 Corrosion resistance\u003c/h2\u003e\u003cp\u003eThe impedance spectra and electrochemical polarization profiles of the coatings in 15 wt% HNO\u003csub\u003e3\u003c/sub\u003e solution are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, while their corresponding corrosion current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003e\u003cem\u003ecorr\u003c/em\u003e\u003c/sub\u003e), corrosion potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ecorr\u003c/em\u003e\u003c/sub\u003e), polarization resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e), and charge transfer resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ect\u003c/em\u003e\u003c/sub\u003e) values are provided in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The corrosion potential and polarization resistance of the coatings initially increased and then followed a decreasing trend as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration was increased, while the corrosion current density showed the opposite trend, first decreasing and then rising. The SCU-0.15 coating displayed the highest corrosion potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ecorr\u003c/em\u003e\u003c/sub\u003e = \u0026minus;\u0026thinsp;0.002 V) and polarization resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e = 1190.3 Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e) among all samples. Moreover, the corrosion current density of the SCU-0.15 coating was the lowest at 30.79 \u0026micro;A/cm\u0026sup2;, indicating its higher corrosion resistance. This outstanding performance is attributed to the coating\u0026rsquo;s dense and homogeneous amorphous structure formed at a CuSO\u003csub\u003e4\u003c/sub\u003e concentration of 0.15 g/L, which lacks grain boundaries, enhancing its corrosion resistance [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Similarly, the corrosion potentials and polarization resistances of the SCU-0.2 and SCU-0.3 coatings were lower, while their corrosion current densities were higher than those of the SCU-0 coating, indicating poorer corrosion resistance. This decline is attributed to the co-deposition of Ni and Cu at CuSO\u003csub\u003e4\u003c/sub\u003e concentrations of 0.2 and 0.3 g/L, which transformed the coating structure from amorphous to a mixed crystalline phase. Therefore, various corrosive microcells formed at the grain boundaries of the microcrystalline structure, accelerating the corrosion process [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eElectrochemical parameters of different coatings.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ecorr\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003cp\u003e(V)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eJ\u003c/em\u003e\u003csub\u003e\u003cem\u003ecorr\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003cp\u003e(\u0026micro;A/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003cp\u003e(Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ect\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003cp\u003e(Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;0.153\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e33.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e746.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4381.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;0.086\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e31.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e952.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4531.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e30.79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1190.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4678.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;0.237\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e34.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e684.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4316.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSCU\u0026minus;0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;0.291\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e34.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e663.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4251.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e shows the electrochemical impedance spectra of the different coatings in 15 wt% HNO\u003csub\u003e3\u003c/sub\u003e solution. All spectra showed similar semicircular shapes, indicating that the corrosion process involves a single time constant. The SCU-0.15 coating indicated the largest arc radius in the impedance spectrum, corresponding to the highest charge transfer resistance of 4678.4 Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e. However, the SCU-0.3 coating showed the smallest arc radius, with a charge transfer resistance of 4251.5 Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e. The results also confirmed that the SCU-0.15 coating exhibited the best corrosion resistance, while the SCU-0.3 coating showed the poorest corrosion resistance [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003e(1)\u0026nbsp;The SCU-0.15 coating exhibited a finer and more compact structure compared to the SCU-0 and SCU-0.1 coatings. Furthermore, with the increase in CuSO\u003csub\u003e4\u003c/sub\u003e concentration, the nodules in the SCU-0.15 coating became smaller and more uniform in size. Furthermore, distinct diffraction peaks corresponding to Cu appeared in the SCU-0.15, SCU-0.2, and SCU-0.3 coatings when the CuSO\u003csub\u003e4\u003c/sub\u003e concentrations reached 0.15, 0.2, and 0.3 g/L. The Cu contents in these coatings were 1.28, 3.82, and 7.43 wt%, respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e(2) The SCU-0.15 and SCU-0.3 coatings exhibited compact and refined cross-sectional morphologies, with coating thicknesses of approximately 68.7 \u0026mu;m and 68.2 \u0026mu;m, respectively.\u0026nbsp;When an appropriate amount of CuSO\u003csub\u003e4\u003c/sub\u003e (0.15 g/L) was added to the plating bath, the coating structure became finer and denser, with the average diameter of the Ni/Cu solid solution measuring approximately 34.6 nm. However, the coating displayed a coarser structure as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration was raised to 0.3 g/L, and the average size of the Ni/Cu solid solution increased to approximately 63.9 nm.\u003c/p\u003e\n\u003cp\u003e(3)\u0026nbsp;The SCU-0, SCU-0.1, and SCU-0.15 coatings displayed only a broad, bun-shaped nickel diffraction peak at 2\u003cem\u003e\u0026theta;\u003c/em\u003e = 45\u0026deg;, indicating that these three coatings possessed amorphous Ni-P structures. When the CuSO\u003csub\u003e4\u003c/sub\u003e concentration reached 0.2 and 0.3 g/L, characteristic diffraction peaks of the Cu element appeared at 2\u003cem\u003e\u0026theta;\u003c/em\u003e = 43.4\u0026deg; and 50.3\u0026deg;, corresponding to the planar directions (111) and (200) of Cu₀.₈₁Ni₀.₁₉, respectively, indicating the formation of numerous Ni/Cu solid solutions in the SCU-0.2 and SCU-0.3 coatings.\u003c/p\u003e\n\u003cp\u003e(4) The SCU-0.15 coating indicated the lowest wear loss among all coatings, while the SCU-0 coating showed the highest wear loss during the wear test.\u0026nbsp;The \u003cem\u003eM\u003csub\u003es\u003c/sub\u003e\u003c/em\u003e value of the coating dropped from 443 to 284 emu/cc\u0026nbsp;as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration\u0026nbsp;was\u0026nbsp;raised from 0 to 0.3 g/L. The SCU-0.15 coating indicated the largest arc radius in the impedance spectrum, corresponding to the highest charge transfer resistance of 4678.4 \u0026Omega;\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e. However, the SCU-0.3 coating showed the smallest arc radius, with a charge transfer resistance of 4251.5 \u0026Omega;\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eDeclaration of interests\u003c/h2\u003e\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eQiang Liand Qiang Zhang wrote the main manuscript text, Zhenghai Han and Jun Hu prepared figures 1-13. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe research is supported by the Heilongjiang Bayi Agricultural University to Introduce Talents (Granted no. XYB202308).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData are contained within the article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJia, Y. et al. Tribological behaviors of electroless nickel-boron coating on titanium alloy surface. \u003cem\u003eChin. J. Mech. Eng.\u003c/em\u003e \u003cb\u003e37\u003c/b\u003e (1), 309\u0026ndash;320 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChowdhury, T. A. XPS studies on electroless as-deposited and annealed Ni-P films. \u003cem\u003eEngineering\u003c/em\u003e \u003cb\u003e16\u003c/b\u003e (5), 123\u0026ndash;133 (2024).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChen, W. X. et al. 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Preparation of the Ni-P composite coating co-deposited by nano TiC particles and evaluation of it's corrosion property. \u003cem\u003eAppl. Surf. Sci.\u003c/em\u003e \u003cb\u003e258\u003c/b\u003e (7), 2597\u0026ndash;2601 (2012).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMa, C. et al. Microstructure, wear and corrosion resistances of Ni\u0026ndash;ZrO\u003csub\u003e2\u003c/sub\u003e\u0026ndash;CeO\u003csub\u003e2\u003c/sub\u003e nanocoatings. \u003cem\u003eCeram. Int.\u003c/em\u003e \u003cb\u003e50\u003c/b\u003e (12), 20949\u0026ndash;20957 (2024).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Electroless plating, Ni/Cu⁃P coating, CuSO4 concentration, Microstructure, Wear resistance, Corrosion resistance","lastPublishedDoi":"10.21203/rs.3.rs-7672725/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7672725/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study focuses on improving the performance of Ni-P coatings by introducing varying concentrations (0.1\u0026ndash;0.3 g/L) into the Ni-P plating solution to deposit Ni/Cu-P coatings. The influence of CuSO\u003csub\u003e4\u003c/sub\u003e concentration on the microstructure, surface roughness, brightness, hardness, wear resistance, corrosion resistance, and magnetic behavior of the coatings was explored. The findings revealed that the SCU-0.15 coating, prepared with 0.15 g/L CuSO\u003csub\u003e4\u003c/sub\u003e, showed a finer and more compact microstructure. Diffraction peaks corresponding to copper were observed in the SCU-0.15, SCU-0.2, and SCU-0.3 coatings. The Cu content in the SCU-0.15 coating was measured at 1.28 wt%. Both the SCU-0.15 and SCU-0.3 coatings displayed compact and fine cross-sectional morphologies, with coating thicknesses of 68.7 \u0026micro;m and 68.2 \u0026micro;m, respectively. TEM measurements revealed that the average diameters of the Ni/Cu solid solution in the SCU-0.15 and SCU-0.3 coatings were approximately 34.6 nm and 63.9 nm, respectively. The SCU-0, SCU-0.1, and SCU-0.15 coatings displayed a broad, bun-shaped nickel diffraction peak at 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;45\u0026deg;, indicating that these coatings possessed an amorphous Ni-P structure. The hardness of the SCU-0 coating was approximately 447.6 HV, whereas the SCU-0.15 coating showed a significantly higher hardness of about 713.5 HV. The SCU-0.15 coating exhibited the lowest wear loss among all the prepared coatings, whereas the SCU-0 coating showed the highest wear loss during wear testing. The saturation magnetization (\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e) of the coatings dropped from 443 to 284 emu/cc as the CuSO\u003csub\u003e4\u003c/sub\u003e concentration was raised from 0.1 to 0.3 g/L. Further, the SCU-0.15 coating demonstrated the highest corrosion potential and polarization resistance compared to the other coatings. Moreover, the SCU-0.15 coating had the lowest corrosion current density at 30.79 \u0026micro;A/cm\u003csup\u003e2\u003c/sup\u003e, indicating excellent corrosion resistance. Furthermore, it showed the largest arc radius in the impedance spectrum and the highest charge transfer resistance of 4678.4 Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e, further confirming its improved corrosion protection performance.\u003c/p\u003e","manuscriptTitle":"Influence of CuSO4 concentration on microstructures and properties of electroless deposited Ni/Cu-P coatings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-09 08:59:55","doi":"10.21203/rs.3.rs-7672725/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-06T11:35:30+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-04T20:37:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-28T08:26:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"120097808053586775446993638407255251232","date":"2025-09-28T06:01:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"189889362393192962218158626903946484080","date":"2025-09-27T20:24:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"333215453564334478702273366254417568152","date":"2025-09-26T18:05:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"302786411142088107975109767542820620628","date":"2025-09-26T13:46:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"277031794091220736779976166912733175394","date":"2025-09-26T04:59:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"58028307203401423330386123930760150836","date":"2025-09-26T04:00:03+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-26T03:56:49+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-09-26T03:11:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-25T01:26:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-23T11:05:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-09-22T09:32:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cd44d9fd-e263-4e7e-b907-afa63e7dc1bc","owner":[],"postedDate":"October 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":56011094,"name":"Physical sciences/Chemistry"},{"id":56011095,"name":"Physical sciences/Engineering"},{"id":56011096,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-03-09T16:14:40+00:00","versionOfRecord":{"articleIdentity":"rs-7672725","link":"https://doi.org/10.1038/s41598-026-42256-x","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-03-06 15:58:01","publishedOnDateReadable":"March 6th, 2026"},"versionCreatedAt":"2025-10-09 08:59:55","video":"","vorDoi":"10.1038/s41598-026-42256-x","vorDoiUrl":"https://doi.org/10.1038/s41598-026-42256-x","workflowStages":[]},"version":"v1","identity":"rs-7672725","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7672725","identity":"rs-7672725","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}