The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings

The influence of surface defects, i.e., droplets and craters, on the mechanical and tribological properties of arc-evaporated V_xN coatings deposited on cemented carbide has been investigated in a scratching contact using a diamond stylus and a sliding contact using a stainless steel pin. Post-test characterisation using 3D optical surface profilometry and scanning electron microscopy was performed in order to investigate the mechanical and tribological response of the coatings. The results show that scratch induced coating cracking mainly is restricted to larger droplets showing a low interfacial bonding to the adjacent coating matrix. The influence of coating defects on the cohesive strength, i.e., the tendency to chipping of small coating fragments, was found to be relatively small. In contrast, the presence of defects may have a significant impact on the interfacial adhesive strength, increasing the tendency to spalling. In sliding contact, surface defects such as droplets and craters have a strong impact on the tribological behaviour of the coatings causing abrasive wear of the less hard counter material surface and material transfer to the coating, both mechanisms affecting the friction characteristics of sliding contact tribo systems.