Effects of Surfactants on Microstructure and Performance of Ni Coatings via Cathodic Plasma Electrolytic Deposition

The stability of the gas film in the cathode plasma electrolytic deposition (CPED) process is essential for producing high-quality coatings. In this work, cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic polyvinylpyrrolidone (PVP) surfactants were added to the electrolyte to regulate the gas film. Force balance analysis of individual bubbles demonstrated that surfactants effectively reduced surface tension, resulting in thinner gas films and lower energy consumption. With 3 g/L of CTAB, SDS, and PVP, energy consumption was reduced by 67.21%, 60.97%, and 73.58%, respectively. Based on the polarity and electrostatic interactions of the surfactants, the mechanisms by which the three surfactants affect gas film uniformity and the deposition process were revealed. CTAB reduced gas film uniformity due to the attraction of opposite charges, leading to cross-sectional defects. In contrast, SDS improved gas film uniformity through the repulsion of negative charges, reducing coating roughness and increased thickness. PVP exhibited intermediate effects, producing dense coatings with slightly lower thickness. This work provides a new perspective for regulating the CPED process and lays the groundwork for exploring alternative methods to stabilize CPED operations.