High quality nanocrystalline tungsten carbide films were deposited by a filtered cathodic vacuum arc technique at room temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystalline structure and surface morphology of the films. Substrate bending methods and nanoindenter were used to measure internal stress, hardness, and Young's modulus of the films. The film structure evolves from a single hexagonal alpha-W2C phase to a mixture phase, which is composed of a hexagonal a-W2C, a cubic WC1-x; and a cubic W phase, as the substrate bias, which is always negative, is increased to 200 V. As the substrate bias is further increased, the. film structure changes gradually to a single alpha-W2C phase again. The variation trends of internal stress, hardness, and Young's modulus with the substrate bias are similar. They increase with substrate bias, reaching a maximum of 7.2, 26, and 270 GPa, respectively, at-a substrate bias of 200 V, then decrease with further increase of substrate bias. (C) 2003 American Vacuum Society.