Gradient TiCN films were deposited in the arc ion plating system with Cr and Ti targets under the mixed Ar, C2H2 and N-2 gases at a temperature of 480 degrees C. In this study, the effect of the C2H2 flow rate on composition, microstructure, bonding energy, hardness, modulus, elasticity, plasticity, adhesion and tribological behaviors of the deposited TiCN films were systematically investigated. The XRD result showed that all the films exhibited a highly textured growth with the (1 1 1) as the preferred orientation along the surface normal. By increasing the flow rate of C2H2, the contents of TiC and TiCN decreased and increased, respectively, which led to a significant decrease in hardness from 62 GPa to 31 GPa. The adhesion strength increased and wear rate decreased due to the decrease of the brittle TiC phase in the films. (C) 2013 Elsevier B.V. All rights reserved.