Mechanical properties and corrosion behaviour after scratch and tribological tests of electrodeposited Co-Mo/TiO2 nano-composite coatings

The micro-mechanical (Young's modulus and hardness) and tribological properties, as well as the scratch resistance of Co-Mo/TiO2 nano-composite coatings were investigated. The coating was found to be harder and stiffer than the substrate (pure cobalt). Low residual stresses were also derived from Stoney's equation (type I stress). The corrosion behaviour after tribological and scratch tests was studied in Ringer's solution. Dry sliding of the coating against an alumina ball at the load of 1 N or 2 N over the same distance had nearly no influence on the anodic branch of the polarisation curves. By contrast, the current density in the cathodic branch (oxygen reduction reaction, ORR) increased significantly as the normal load of the sliding contact increased. Severe damage induced during scratch tests (with loads from 0 to 30 N) caused an increase in the current density, both in the anodic and cathodic branches. This increase was more pronounced in the cathodic domain (ORR).