Influence of B4C Nanoparticles on Corrosion Characteristics of Ni Matrix Nanocomposite Coatings Fabricated via Pulse Electroplating Technique

The Ni-B4C nanocomposite coatings were fabricated via pulse electrodeposition on a copper substrate, and the effects of pulse current density, duty cycle, and pulse frequency on the microstructure, morphology, and corrosion characteristics were assessed. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) tests were employed. The baseline electrodeposition conditions were set at i = 1 A/dm², γ = 50%, and f = 10 Hz. Embedding B4C nanoparticles (NPs) into the nickel matrix significantly reduced the nickel crystallite size for the primary (111) and (200) crystal planes. Increasing the pulse current density from 1 to 4 A/dm² caused a substantial decrease in the incorporation rate of B4C NPs, from 5.5 to 2.9 vol.%. However, an increase in the duty cycle from 25 to 50% and the pulse frequency from 1 to 10 Hz raised the incorporation rate to 5.5 vol.% and 4.6 to 3.9 vol.%, respectively. Surprisingly, the incorporation of B4C led to an increase in the corrosion current density from 2.301 to 4.541 µA/cm². Increasing the pulse current density from 1 to 4 A/dm² and the duty cycle from 25 to 50% notably decreased the corrosion current density from 4.541 to 1.375 µA/cm² and from 7.243 to 4.541 µA/cm², respectively. Conversely, the minimum corrosion current density of 0.599 µA/cm², deposited at 1 Hz, increased significantly to 4.541 µA/cm² at 10 Hz, while the B4C NPs content increased from 3.9 to 5.5 vol.%, possibly due to a more uniform distribution of B4C NPs at 1 Hz. The Ni-B4C specimen deposited at 1 Hz exhibited a higher Rct compared to the pure nickel sample under baseline conditions, indicating strong consistency between the EIS and potentiodynamic results.