Thermal‑sprayed WC‑NiMoCrFeCo/vapor‑deposited DLC with a composition‑structure dual‑gradient transition layer: Synergistic corrosion and wear protection for marine environments

Abstract

To tackle the synergistic corrosion‑wear degradation of moving components in marine environments, we propose a composite coating system consisting of a WC‑NiMoCrFeCo (WN) underlayer, a diamond‑like carbon (DLC) top coat, and a composition‑structure multi-gradient transition layer (MTL) fabricated by hybrid high‑velocity oxy‑fuel spraying and vapor deposition. The MTL is designed to bridge the severe mismatch in elastic modulus and thermal expansion between the WN layer and the brittle DLC film, thereby suppressing interfacial cracking and delamination. Electrochemical impedance spectroscopy demonstrates that this architecture retains a high polarization resistance (>10 5 Ω·cm 2 ) even after 108 days of immersion in simulated seawater, owing to the concerted effects of physical barrier, gradient‑modulated potential distribution, and chemical passivation. More importantly, the coating exhibits a unique failure‑buffering behavior: the MTL effectively confines local damage to the DLC top layer and prevents its propagation into large‑scale spallation.Even after prolonged sliding, the remaining DLC regions continue to undergo friction‑induced controlled graphitization, forming a low‑shear tribofilm that maintains stable lubrication and protects the underlying material from abrupt failure. This work demonstrates that the dual‑gradient interface design, coupled with the self‑adaptive tribological response of DLC, offers a promising route for achieving long‑term corrosion and wear protection in harsh marine service conditions.