Dlc Duplex Coating On High-Speed Tool-Steel Substrates Using Plasma Nitrocarburizing After Radical Nitriding

Diamond-like carbon (DLC) is applied to a wide variety of fields in the industry because of its tribological properties and hardness. However, one of the major issues is the adhesion strength between DLC films and the metal substrate. Many efforts have been made to obtain a higher adhesion strength, such as the formation of an interlayer and the modification of the surface layer. In contrast, radical nitriding is one of the most suitable methods for the pretreatment of duplex coatings, because it makes it possible to increase the surface hardness while maintaining the roughness of the original surface. According to this process, a diffusion layer is formed in the surface region using state plasma control. In the present investigation, we used existing hot-wall plasma nitriding equipment to treat high-speed tool steel using both plasma nitrocarburizing and radical nitriding to forma DLC film. Our results indicated that radical nitriding formed a nitrogen-diffusion layer, followed by the formation of a carbon layer by nitrocarburizing without the formation of a brittle compound layer. It maintained surface roughness compared with the untreated substrate. Although the hardness of the steel did not improve, the resulting DLC films exhibited better adhesion to the treated-steel substrates than to the untreated ones.