Investigation of the corrosion stability of TiCN and diamond-like carbon(DLC) coatings on 304 stainless steel in simulated seawater: Electrochemical and numerical studies

High-velocity multiphase flow containing dissolved oxygen and chloride ions leads to severe frictional loss and corrosion degradation in hollow fountain nozzles. To enhance flow-channel performance, titanium carbonitride (TiCN, T1) and diamond-like carbon (DLC, T2) coatings were deposited on 304 stainless steel using multi-arc ion plating with a graded Ti/TiN/TiCN transition layer. Structural, surface, and interface properties were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, FE-SEM, and 3D profilometry, while corrosion resistance in ASTM D1141 simulated seawater was evaluated via potentiodynamic polarization and electrochemical impedance spectroscopy. ANSYS Fluent simulations were further employed to assess coating-induced flow improvements. The DLC coating demonstrated a higher sp³ fraction (ID/IG =0.5), significantly smoother morphology (Ra≈42.5 nm), and the best corrosion resistance, with a corrosion current density of 0.12 μA/cm² and a charge-transfer resistance of 13230 Ω·cm². Numerical analysis confirmed that the DLC-coated surface effectively suppressed near-wall turbulence, stabilized the high-velocity jet core, and reduced gas–liquid mixing.Overall, DLC achieved a synergistic combination of “ultra-low friction” and “high corrosion resistance,” providing a promising and durable surface-engineering solution for improving jet stability and prolonging the service life of fountain nozzles and related hydraulic components.