Construction of a hierarchical h-BN/DLC composite coating on Ce-doped plasma electrolytic oxidation film for enhanced corrosion resistance of aluminum alloy

To address the inherent microporosity and inadequate long-term corrosion protection capacity of plasma electrolytic oxidation (PEO) ceramic coatings deposited on 6063 aluminum alloy substrates, a hierarchical Ce-doped PEO/h-BN/diamondlike carbon (DLC) composite coating architecture was fabricated via combined hydrothermal pore sealing and plasma enhanced chemical vapor deposition (PECVD) post treatment routes. The microstructure, chemical composition, and corrosion behavior of the coatings were systematically characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results demonstrated that hydrothermal treatment effectively introduced h-BN nanosheets into discharge channels and the micropores of the Ce-doped PEO coating. XPS, Raman, and FT-IR analyses confirmed the successful incorporation of h-BN while preserving its characteristic layered structure. Subsequently, a continuous DLC film containing typical sp 2 /sp 3 hybridized carbon bonds was successfully deposited by PECVD. Among all tested processing parameter combinations, the composite coating modified with 1 g L −1 h-BN hydrothermal sealing followed by 60 min PECVD deposition delivered optimal comprehensive anticorrosion performance, featured by a minimum corrosion current density of 1.76 × 10 −9  A cm −2 and the highest impedance response in 3.5 wt% NaCl solution. The significantly improved anticorrosion performance originates from the dual synergistic barrier effect derived from h-BN nanosheet pore plugging and the dense DLC outer capping layer. Specifically, h-BN nanosheets effectively reduced pore connectivity and prolonged the diffusion path of corrosive species, whereas the dense DLC overlayer served as additional physical barrier that suppressed electrolyte penetration and interfacial charge transfer. This study provides valuable experimental guidance and theoretical support for the design of graded ceramic-carbon composite protective coatings for aluminum alloys serving in high chloride marine environments.