Investigation of the Microstructure and Properties of Cage-Shaped Hollow Cathode Bias Voltage Modulated Si-Doped DLC Thick Film

To mitigate the high residual stress inherent in single-layer diamond-like carbon (DLC) films, we fabricate alternating soft/hard multilayer DLC thick films using a cage-type hollow cathode plasma-enhanced chemical vapor deposition (PECVD) system. The microstructure, mechanical properties, and corrosion resistance of these films were systematically investigated. Periodic film structures were characterized via scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), and X-Ray photoelectron spectroscopy (XPS). Adhesion and hardness were evaluated using a scratch tester and a nanoindentation tester, respectively, while corrosion resistance was assessed by dynamic potential polarization tests in a 3.5 wt% NaCl solution. Findings indicate that as the modulation period of the Si-DLC films increases, a greater proportion of high-energy carbon particles penetrate the non-biased layer under workpiece bias, ultimately disrupting the layered structure in the 90-layer film. This results in densification, reflected in three key improvements: (1) an increase in sp3-bonded carbon content and enhanced smoothness, (2) enhanced adhesion (from 34 N to 46 N) and nanohardness (from 4.94 GPa to 8.41 GPa), and (3) a tenfold reduction in corrosion current density (icorr) compared to single-layer Si-DLC films.