Microstructure evolution and age hardening in (Ti,Si)(C,N) thin films deposited by cathodic arc evaporation

Ti1-xSixCyN1-y films have been deposited by reactive cathodic arc evaporation onto cemented carbide substrates. The films were characterized by X-ray diffraction, elastic recoil detection analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron-energy loss spectroscopy and nanoindentation. Reactive arc evaporation in a mixed CH4 and N2 gas gave films with 0 ≤ x ≤ 0.13 and 0 ≤ y ≤ 0.27. All films had the NaCl-structure with a dense columnar microstructure, containing a featherlike pattern of nanocrystalline grains for high Si and C contents. The film hardness was 32-40 GPa. Films with x > 0 and y > 0 exhibited age-hardening up to 35-44 GPa when isothermally annealed up to 900 oC. The temperature threshold for over-ageing was decreased to 700 oC with increasing C and Si content, due to migration of Co, W and Cr from the substrate to the film, and loss of Si. The diffusion pathway was tied to grain boundaries provided by the featherlike substructure.