Ti 1−x Si x C y N 1−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 CH 4 and N 2 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 32–40GPa. Films with x>0 and y>0 exhibited age-hardening up to 35–44GPa when isothermally annealed up to 900°C. The temperature threshold for over-ageing was decreased to 700°C 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.