A comparative study of the mechanical and tribological properties of PECVD single layer and compositionally graded TiSiCN coatings

In this study, TiSiCN coatings, with and without a Ti/TiN/TiCN interlayer, are deposited on tempered and plasma-nitrided H13 hot-working tool steel substrate by pulsed direct current plasma enhanced chemical vapor deposition. The self-lubricant super hard TiSiCN coatings have a nanocomposite structure consisting of an amorphous SiCN matrix embedding TiCN nanocrystals. In the presence of the graded interlayer, coating adhesion improves significantly, as revealed by a 40% increase of the critical load for adhesion failure in scratch testing of the coated samples. The formation of shorter radial cracks around the indentation zone during Rockwell C indentation test reveals that the coating with the graded interlayer has a higher toughness compared to the single layer coating. The wear rate of the graded coating is found to be about three times lower than that of the single layer coating, which can be attributed to the higher hardness, better adhesion to the substrate and higher toughness of the graded coating.