Mechanical and tribocorrosion properties of HVOF sprayed WC–Co coatings

HVOF technology has been proposed in recent years for the production of engineered cermet coatings suitable for the replacement of hard chromium surface treatments of mechanical components, for aeronautical and automotive applications. The aim of this study has been to compare the mechanical and tribocorrosion properties of WC–Co cermet coatings fabricated with different processing parameters, to optimise the spraying process by evaluating the dependence of the macroscopic coating properties on the spraying procedure. Barrel length, oxygen:fuel ratio and torc–/specimen spraying distance were selected as the main variables since their influence on coating microstructure and macroscopic properties in the absence of corrosion is already well known. WC–Co samples were subjected to 'block on ring' wear testing, carried out in an electrochemical cell, to assess wear properties in combination with a range of corrosive conditions. The results were compared to those obtained by ordinary wear testing and electrochemical characterisation. Mechanical properties of the coatings, such as microhardness, fracture toughness and coating–substrate adhesion, were also measured. Tribocorrosion testing proved better able to distinguish coating properties than conventional wear tests, due to the more severe damage induced by the corrosive attack.