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

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.