Growth, microstructure, and mechanical properties of arc evaporated TiCxN1−x (0≤x≤1) films

TiCxN1−x films with x ranging from 0 to 1 were grown by arc evaporation by varying the flow ratio between the reactive gases. The substrates were cemented carbide inserts (WC-6 wt.% Co) which were negatively biased at 400 V, resulting in a deposition temperature of ∼550°C. The film composition, as measured by glow discharge optical emission spectroscopy, was found to vary almost linearly with the gas flow ratio. Cross-sectional transmission electron microscopy in combination with X-ray diffraction (XRD) showed that the films were of single-phase NaCl-structure with a dense columnar microstructure. The intrinsic stress analyzed using the XRD sin2ψ method, was found to have a maximum of −5.9 GPa in the composition range of 0.4≤x≤0.7 which correlated with a maximum in XRD peak broadening due to inhomogeneous strains. The hardness and Young’s modulus of the as-deposited TiCxN1−x films were measured by the nanoindentation technique. A maximum in hardness of 45 GPa was found at the same composition range (0.4≤x≤0.7) as the intrinsic stress maximum. The hardness for x=0 (TiN) and x=1 (TiC) were found to be 28 and 36 GPa, respectively. The Young’s modulus was constant ∼610 GPa for films with compositions up to x=0.6, thereafter it decreased to 540 GPa at x=1. The increase in intrinsic stress with increasing carbon content is suggested to be due to increased stability of defects created from the collision cascade or/and by a change in the defect structure itself. The fact that hardness showed a maximum at the same composition as residual stress and FWHM indicates that obstruction on dislocation movement has a major influence on the hardness of these films.