The Influence of the Pretreatment of Tool Steel on the Running‐In Phase of Diamond‐Like Carbon Coatings

Low friction and wear of diamond‐like carbon (DLC) coatings strongly depend on the running‐in phase, which is significantly affected by surface pretreatment. In tool steels, differences in hardness and sputtering rates between carbides and the steel matrix may cause carbide protrusion during polishing and ion etching, leading to increased coating roughness. Although considerable attention has been devoted to optimizing DLC deposition parameters, the influence of surface pretreatment is often overlooked despite its significant effect on tribological performance. In this study, a TiNb‐DLC coating consisting of an amorphous hydrogenated carbon matrix (a‐C) doped with titanium and niobium was deposited on X153CrMoV12 (AISI D2) tool steel by reactive magnetron sputtering. Tribological properties were evaluated using a pin‐on‐disc test, while chemical and structural characterization was performed by EDS, XRD, Raman spectroscopy, and XPS. Reducing the ion etching time decreased the coefficient of friction by 18% and coating wear by 70% during the running‐in phase. Post‐deposition polishing further reduced the coefficient of friction by 51%, wear of the steel counterpart by 71%, and wear of the TiNb‐DLC coating by 91%. The results demonstrate the critical role of surface pretreatment in controlling the tribological behavior of DLC coatings.