Interface and superhardness of TiN/CNx multilayer films

This work attempts to reveal the microstructure of interface and the relation between interface mixing and hardening mechanism in TiN/CNx multilayer films. The growth and microstructure of these interfacial layers are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Investigation result indicates that the interface species are mainly composed of Ti–C–N, the growth of interlayer mainly depends on the deposition temperature. The thickest interlayer (about 2.5 nm) is produced at 300 °C, and the interlayer disappears at 500 °C. Nanoindentation testing indicates that the film with a maximum interlayer thickness of about 2.5 nm exhibits superhardness up to 40 GPa. Based on the experimental results, it is suggested that the interfacial intermixing and the crystal quality of TiN are the main reasons for the superhardness effect in TiN/CNx nanostructured multilayers.