A comparative study on the microstructure and surface property evaluation of coatings produced from nanostructured and conventional WC–Co powders HVOF-sprayed on Al7075

• WC–12Co nanopowder was successfully HVOF sprayed on Al7075 corrosion/wear-wise.
• “Nano” WC–12Co shows better corrosion/wear behaviour than “micro” WC–12Co coating.
• Mechanisms of localized/general corrosion and sliding wear behaviour are analysed.
• Key corrosion reducing factors: fine carbide distribution, binder homogeneity
• Key wear reducing factors: fine carbide distribution, strong intersplat bonding

Conventional and nanostructured WC-12 wt.% Co powders were HVOF sprayed on Al7075-T6. The nanocoatings presented slightly less microporosity, higher microhardness, higher fracture toughness but higher decarburization, than the conventional ones. The nanocoatings exhibited greater resistance to general corrosion and localized corrosion in 3.5% NaCl than their conventional counterparts. Other than an occasional removal of WC nanoparticles, corrosion modes appeared similar for both types of coatings, characterized by selective dissolution of Co, formation of protective surface films and crevice corrosion along interlayer boundaries. Both types of coatings exhibited high dry sliding wear resistance. Nevertheless, the wear performance of the nanocoatings was even superior than that of their conventional counterparts. Main wear modes included plastic deformation of binder, oxidative wear leading to the formation of lubricating oxides and adhesive wear leading to the formation of alumina-rich surface depositions (from the Al2O3 counter balls). Coating of Al7075 with nano WC–12Co was proved effective in terms of microstructural features, corrosion and wear behaviour.