TiN/SiNx nanocomposite layers with Si contents between 0 and 25 at. % were deposited by a reactive arc-magnetron sputtering hybrid process. The stoichiometry of the SiNx phase was found to be related to the silicon sputter target state, i.e., elemental or nitrided. TiN/SiNx layers with a Si:N ratio close to 0.75 (silicon nitride) show a hardness maximum at overall Si contents between 5 and 7 at. %. The hardness maximum is absent for nitrogen deficient stoichiometries of SiNx. The oxidation resistance of the composite, layers is three to five times better than that of pure TiN. In contrast to the effect of the stoichiometry on hardness, the oxidation resistance depends on the overall silicon content only, regardless of stoichiometry. (C) 2004 American Vacuum Society.