Improved interfacial adhesion between TiAlN/DLC multi-layered coatings by controlling the morphology via bias

By combining the advantages of the thermo-mechanical properties of TiAlN and self-lubricating properties of diamond-like carbon (DLC), a multi-layered TiAlN/DLC coating is fabricated by filtered cathodic vacuum arc and magnetron sputtering. According to the different morphology and mismatch between the physical and chemical properties of TiAlN and DLC, multiple methods are used to study the growth mechanism of crystalline TiAlN and amorphous DLC in the combined system. The morphology evolution depending on the bias is studied and the brittle interface is assessed by scratch experiments. The results show that an interlamination failure occurs at the top of first DLC layer due to the cluster morphology obtained by small bias, however, the failure moves to the interface above the substrate when the clusters are refined by increasing bias. By adopting the stepwise decreased bias, the 4.5 μm thick TiAlN/DLC multi-layer coating is fabricated and does not exhibit interfacial failure at any interface between TiAlN and DLC in the scratch experiments up to a load of 100 N. Excellent adhesion (Lc = 63 N) is also achieved from coatings deposited on high-speed steel with optimized Cr/CrCx/CrC interlayers prepared by high-power impulse magnetron sputtering.