Effect of trace nickel ions on trivalent chromium deposition

Chromium electrodeposition, a pivotal technique for fabricating functional coatings and high-purity chromium, holds significant industrial value. Compared to traditional hexavalent chromium systems, the trivalent chromium electrodeposition process, as a mainstream technology in surface engineering, demonstrates remarkable advantages in environmental friendliness and energy efficiency. In this study, Ni-Cr alloy coatings with a nickel content of 12.2 wt% were successfully fabricated on copper substrates based on metal co-deposition theory. Cyclic voltammetry analysis revealed a reduction potential difference of between Ni²⁺ and Cr³ ⁺, indicating significant synergistic deposition effects. X-ray diffraction patterns showed no obvious diffraction peaks appeared in all the plated samples, while selected-area electron diffraction in transmission electron microscopy exhibited diffuse halo patterns, collectively confirming the typical amorphous structure of the coating. Confocal microscopy analysis demonstrated a surface roughness ( S _a ) of 0.048μm for the Ni-Cr coating, significantly lower than that of pure Cr coatings ( S _a =0.076μm). Electrochemical impedance spectroscopy revealed a charge transfer resistance of 891.2 Ω/cm² under open circuit potential (compared to 350.6 Ω/cm² for Cr coating), and Tafel curve analysis yielded a i _corr of 9.7 μA/cm², compared to 26.4 μA/cm² for Cr coating. These results demonstrate that the enhanced corrosion resistance originates from the synergistic effects of the isotropic characteristics of the amorphous structure and the dense surface morphology.