Insights into the Corrosion and Tribocorrosion Behaviors of DLC-Modified WC-Based Cermet Duplex Coatings

To gain deeper insight into the protective mechanism of tungsten carbide/diamond-like carbon (WC/DLC) duplex coatings, this study employed high-velocity oxygen-fuel (HVOF) combined with linear ion source (LIS) technology to deposit the WC/DLC duplex coating on the Ti6Al4V substrate. Their tribocorrosion behaviors were thoroughly investigated. The results show that the dense, uniform, and chemically inert DLC top layer acts as an effective barrier, preventing the corrosive medium from penetrating into the underlying WC cermet layer through pores. Consequently, the duplex coating exhibits a lower Icorr of 3.54 × 10−8 A/cm2, compared with that of the single WC coating (1.08 × 10−6 A/cm2), demonstrating significantly improved corrosion resistance. Moreover, the DLC coating offers excellent tribological performance owing to the high hardness and self-lubricating characteristics. After depositing the DLC top layer on the HVOF-sprayed WC cermet, the COF is reduced to ~0.08, and the wear rate reaches only 5.64 × 10−8 mm3/N·m, indicating notably enhanced tribocorrosion resistance. In short, in such HVOF-PVD/CVD duplex coating systems, the PVD/CVD functional layer can improve the tribocorrosion performance of the HVOF interlayer by leveraging its intrinsic advantages, such as high hardness, low friction, dense and uniform microstructure, and chemical inertness.