HVOF-sprayedWC–CoCr coatings on Al alloy: Effect of the coating thickness on the tribological properties

The microstructure, the micromechanical properties, the wear behaviour and the impact resistance ofWC–CoCr cermet coatings, deposited onto an aluminium alloy substrate by High Velocity Oxygen-Fuel(HVOF) flame-spraying,were examined as a function of the coating thickness, whichwas varied between50mand 150mby performing different numbers of scans of the HVOF torch in front of the substrate.The coatings became denser and significantly harder as the number of torch scans increased: the analysisof singleWC–CoCr splats by combined SEM and Focused Ion Beam (FIB) techniques enabled the interpretationof the mechanisms underlying this phenomenon. In accordance to such densification, the slidingwear resistance increased with the number of torch scans, as abrasive grooving and brittle failure mechanisms were progressively suppressed. The resistance to cyclic impact was also enhanced. In comparison to anodised films, theWC–CoCr coatings appeared much more resistant against wear and cyclic impact; specifically, three torch scans seem enough to produce a coating having suitable characteristics.