Wear and corrosion behaviour of HVOF WC-CoCr / CVD DLC hybrid coating systems deposited onto aluminum substrate

Hybrid coating systems consisting of a HVOF-sprayed WC–CoCr interlayer (75 μm or 125 μm thick) and a thinDLC-based top layer (obtained by electron cyclotron wave resonance–chemical vapour deposition: ECWRCVD)were deposited onto AA6082-T6 substrates; their tribological and anti-corrosion performances wereevaluated and compared to those of the DLC film deposited directly onto the Al alloy substrate withoutinterlayer.In scratch adhesion testing, the interlayer delays the onset of cracking and spallation of the film, because itprovides better mechanical support than the bare Al substrate. As soon as cracking begins, however, completedelamination of the films deposited on cermet interlayers occurs, revealing limited interface adhesion.Accordingly, in ball-on-disk wear tests, the films deposited on cermet interlayers can stand more severecontact conditions without cracking, but, as the contact pressure increases, most of the film delaminates.If no cracking occurs, the film is very effective at producing low wear and low friction, but it is not as effectiveat preventing penetration of corrosive agents, as shown by corrosion tests in aqueous environments, becauseit contains some small defects.