Influence of residual stresses on the mechanical properties of TiCxN1-x (x=0, 0.15, 0.45) thin films deposited by arc evaporation

The influence of residual stress state and composition on the mechanical properties of are evaporated TiCxN1-x thin films have been investigated. By controlling the flow ratios of the reactive gases, N-2 and CH4, films with compositions x = 0 (TiN), x similar to 0.15, and x similar to 0.45 have been grown on cemented carbide substrates. The residual stress state was altered through variations in the negative substrate bias over the range 20 V less than or equal to V-s less than or equal to 820 V. The intrinsic stress, sigma(int), measured by the X-ray diffraction (XRD) sin(2)psi method was compressive and increased with decreasing V-s and increasing x. The latter behavior is suggested to be due to increased effective stability of defect complexes when the carbon content increases. Maximum stress level was between -6 and -7 GPa and limited by interior cracking of the films. The increase in intrinsic stress was accompanied by an increase in XRD peak broadening due to inhomogeneous strains. The hardness, H, and Young's modulus, E, of as-deposited films were measured using the nanoindentation technique, Apparently linear correlations between sigma(int) and H were found for each film composition where H increased with x. The maximum H, 44 GPa, was thus obtained for the x similar to 0.45 film with sigma(int) = -5.5 GPa. The lowest hardness for this composition was 35 GPa for a film with sigma(int) = - 2.7 GPa. For the TiN films, a similar variation in hardness of 33 GPa at sigma(int) = -5.8 to 26 GPa at sigma(int) = - 1.2 GPa was obtained. E was constant at similar to 610 GPa for most of the films, with a slight decrease in the films with the lowest sigma(int) values. (C) 2000 Elsevier Science S.A. All rights reserved.