Interfacial Layer Effect on the Adhesion of the Ultra-Hard Thick TAC Film Deposition

Carbon-based thin film tool coatings, such as diamond-like carbon (DLC), have excellent lowfriction and anti-sticking properties. These thin films are widely used for the cutting and machining of increasingly widely-used lightweight non-metallic and non-ferrous metal materials, as a part of countermeasures against global warming. However, non-metallic and non-ferrous metal materials are significantly inferior in strength and heat resistance compared to iron-based metals. Therefore, they are primarily employed in high-content fiber reinforced composite materials, which significantly improves their mechanical and thermal properties. Tetrahedral amorphous carbon (TAC) coating has a hardness level similar to diamond coating. However, when TAC is deposited as a thick film, delamination of the coating layer may occur because of the high internal compressive stress between the carbide-based substrate and coating layer, thereby restricting its scalability to other applications. Other factors to be controlled for thick film TAC deposition include minimizing droplets generated during the coating process, and improving interfacial properties like hardness and fatigue resistance. Here, C in the form of CH4, which has high solubility over Cr and forms various compounds, was added during the interfacial deposition process, between the carbide and TAC, to improve interfacial strength and adhesion by precipitation of carbide at the interface. This eventually led to thick TAC film with the thickness and adhesion of commercially viable thick film.