Thermally Sprayed Coatings as Interlayersfor DLC-Based Thin Films

This article examines the usefulness of a thick thermally sprayed interlayer (plasma-sprayed Ni-50%Cr,plasma-sprayed Al2O3-13%TiO2, or high-velocity oxygen-fuel-sprayed WC-17%Co) for enhancing thewear resistance and the corrosion protectiveness of a diamond-like carbon (DLC)-based thin filmdeposited onto a carbon steel substrate. Scratch tests indicate that the Al2O3-13%TiO2 and WC-17%Cointerlayers definitely increase the critical spallation load of the thin film, but the Al2O3-13%TiO2interlayer itself undergoes brittle fracture under high-contact loads. Accordingly, during ball-on-disktests at room temperature, no cracking and spallation occur in the DLC-based film deposited onto theWC-17%Co interlayer, whereas the one onto the Al2O3-13%TiO2 interlayer is rapidly removed becausethe interlayer itself is fractured. At 300°C, by contrast, the DLC-based film on the Al2O3-13%TiO2interlayer offers the best tribological performance, possibly thanks to the increased toughness of theceramic interlayer at this temperature. Electrochemical polarization tests indicate that the thin film/WC-Co systems possess the lowest corrosion current density.