Adhesion of TiC and Ti(C,N) coatings on steel

The scratch test has been used to measure the adhesion of CVD TiC coatings on various steels by comparing the critical load factors. The critical load (Lc) of a coating–substrate interface determined by the scratch test depends not only on the adhesion but also the substrate hardness and coating thickness. For identical deposition conditions, the coating thickness depends strongly on the carbide forming elements in the steel. In this work, a careful separation of these effects has allowed us to quantify the adhesion of a given system from the critical load. Of the nine steels tested, two had improved adhesion which was shown to be caused by diffusion of substrate elements into the coating. Adhesion measurements of Ti(C,N) coatings deposited by PVD are discussed and compared to the adhesion values of CVD TiC on the same steel substrates.