Evaluation of the corrosion protection effect of amorphous carbon coating through the corrosion behaviors on different substrates

One of the most straightforward and efficient approaches to enhance the corrosion resistance of the initial coatings is by applying an additional top-layer. In this work, a pure a-C:H coating (HDLC) and an a-C:H coating with a submicron-thickness a-C:H:SiOx top-layer (SiCOH) were fabricated on the substrates of 316 L stainless steel (SS 316), 304 stainless steel (SS 304), 45 steel and GCr15 bearing steel (GCr15). The electrochemical corrosion behaviors of the two coatings deposited on the mentioned substrates were studied in a 3.5 wt% NaCl solution. The findings revealed that SiCOH, compared to HDLC, exhibits higher polarization resistance and lower porosity across all tested substrates, indicating a beneficial protective effect of the a-C:H:SiOx top-layer on HDLC surfaces. The top-layer, characterized by higher sp3 carbon hybridization and the presence of insulating silicon oxide, significantly contributes to the corrosion resistance of the coating. Furthermore, the top-layer design enhances the coating's heterojunction, addressing inherent defects and pinholes in HDLC. This effectively obstructs the diffusion path (porosity) of the corrosive medium, substantially improving the corrosion resistance of the HDLC coating.