Tribological Performance of Diamond/Diamond-like Composite Coatings in Simulated Seawater Environment
Silicon carbide mechanical seal rings in marine rotary equipment suffer severe wear, demanding coatings that simultaneously deliver high hardness, low friction, and corrosion resistance. This study fabricates diamond/diamond-like carbon (DLC) duplex coatings via hot-filament chemical vapor deposition (HFCVD) followed by magnetron-sputter-assisted ion-beam deposition. Microcrystalline diamond (MCD) and ultra-nanocrystalline diamond (UNCD) underlayers are grown on SiC, then capped with a hydrogenated DLC lubricating topcoat, forming a rigid-underlayer/lubricating-top-layer architecture. Tribological tests in simulated seawater reveal that DLC reduces MCD surface roughness from 155.33 nm to 123.77 nm and UNCD roughness from 92.43 nm to 81.90 nm. The MCD/DLC coating lowers steady-state friction coefficient and specific wear rate by 32.08% and 12.22%, respectively; UNCD/DLC achieves 26.67% and 20.92% improvements. SEM, Raman, and XPS analyses of worn surfaces indicate that the DLC top layer mitigates interfacial shear stress, enhances boundary lubrication, and accelerates friction-induced graphitization. The composite coating also reduces counterface ball damage and debris accumulation, extending the service life of mating components. These findings demonstrate that the duplex architecture overcomes the inherent limitations of monolithic diamond coatings, offering a viable route for durable marine seal applications.