Enhancement of Corrosion Resistance in 304 Stainless Steel Through Hybrid Parylene C–ALD Al2O3 Composite Coatings

Parylene C films are subjected to inadequate corrosion resistance due to their relatively low adhesion and structural defects. To address this challenge, the CVD Parylene C film (10 μm thick) was composited with Al2O3 film (30 nm thick) prepared with atomic layer deposition (ALD) technology in this work. Optical microscopic results indicate uniform thickness of the films and the reduced adhesion of Parylene C based thick films. SEM-EDX and AFM results show that the composite films have more blurred mounds morphology than the individual films, and Al2O3 film decreases the surface roughness of Parylene C film; compared with the single-layer film, the Ra value of the bilayer film decreased by approximately 6%. XPS, FTIR and XRD analyses confirm the structural components of Al2O3 and Parylene C films and the annealing effect of ALD process on Parylene C film. Tafel polarization and electrochemical impedance spectroscopy tests reveal that the 304-Parylene C–Al2O3 system exhibits the optimal corrosion resistance; its corrosion current density (icorr) is 8.099 × 10−5 μA/cm2 and the ALD Al2O3 thin film uniformly coats the Parylene C film, enhancing its physical barrier and chemical passivation under corrosive conditions.