Ternary Ti-Mo-N and new quaternary Ti-Mo-Si-N coatings were synthesized on substrates (AISI D2) and Si wafers by a hybrid coating system of an arc-ion plating technique using a Ti target and a dc magnetron sputtering technique using Mo and Si targets in N-2/Ar gaseous mixture. The ternary Ti-Mo-N coatings were substitutional solid solutions of (Ti,Mo)N and showed maximum hardness of about 30 GPa at a Mo content of similar to 10 at. %. With the addition of Si, the Ti-Mo-Si-N coating transformed into a nanocomposite consisting of fine (Ti,Mo)N crystallites and an amorphous Si3N4 phase. The hardness of the Ti-Mo-Si(8.8 at. %)-N coatings significantly increased to similar to 48 GPa due to the microstructural change to the nanocomposite containing finer (Ti,Mo)N crystallites by the grain-size refinement effect of Si addition. The averaged friction coefficient of the Ti-Mo-Si-N coatings gradually decreased by increasing the Si content in the Ti-Mo-N coating. The microstructures of Ti-Mo-Si-N coatings were investigated with instrumental analyses of x-ray diffraction, x-ray photoelectron, and high-resolution transmission electron microscopy. In this work, the authors also investigated the effects of substrate bias voltage during deposition on the microstructure and mechanical property of Ti-Mo-Si-N coatings. (C) 2008 American Vacuum Society.