Construction of a stable O₂/H₂O plasma jet rich in highly reactive oxidizing species and enhanced surface modification effects on heterogeneous surfaces

Abstract In this study, a stable O₂/H₂O plasma jet abundant in highly reactive oxidative species is constructed, and the synergistic enhancement mechanism of its hydrophilic modification on heterostructured SiCp/Al composite surfaces is investigated. The effects of gas flow rate, input voltage, and discharge frequency on jet stability, length, and temperature are systematically investigated by a bare-electrode needle-ring configuration, yielding optimal operating parameters. A coupled multi-physics simulation model integrating neutral gas dynamics and plasma discharge is developed to reveal the spatiotemporal evolution of the production rates and number densities of key reactive species (O, ·OH, H₂O⁺, etc.), as well as their regulation mechanisms by gas flow rate and applied voltage. Contact angle measurements are performed to compare the hydrophilic modification performance of O₂/H₂O mixed plasma on the SiCp/Al composite, Al alloy and SiC. The results indicate that the ionization efficiency is dominated by the discharge voltage, while gas flow rate plays a secondary role by modulating the distribution of electronegative species and convective diffusion. Abundant ·OH radicals and excited oxygen species are generated in the O₂/H₂O plasma system, which delivers a significantly higher modification efficiency than pure O₂ plasma. Because of the intrinsic heterogeneous microstructure, the SiCp/Al composite presents enhanced surface wettability compared with homogeneous Al and SiC before plasma treatment. Over the roughness range of 40–100 nm for the SiCp/Al composite, plasma-induced chemical modification dominates the wettability, whereas the heterogeneous height difference structure has no significant influence. The findings of the study provide theoretical and experimental support for the efficient and stable regulation of surface wettability of metal matrix composites via plasma treatment.