A duplex coating system, consisting of a laser-cladded Fe-Cr-based interlayer and a silicon-doped diamond-like carbon (Si-DLC) top layer, was deposited on medium carbon steel substrate using laser cladding (LC) followed by plasma-enhanced chemical vapor deposition (PECVD). The LC interlayer (thickness of 1.5 mm, hardness of 455–620 HV0.3) was applied on both argon ion-etched and non-etched substrate surfaces. The microstructure and adhesion strength of the coatings were systematically investigated. The results show that the LC interlayer significantly enhanced the mechanical support for the Si-DLC coating, increasing adhesion strength by 4~5 times compared to direct deposition. Argon ion etching introduced micro-roughened surface features, increasing interfacial contact area and further boosting adhesion. A synergistic effect was observed between substrate hardness and ion etching in enhancing Si-DLC coating adhesion.

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 (i_corr) compared to single-layer Si-DLC films.