Nanohardness of nanocrystalline TiN thin films

TiN films were prepared by ion beam assisted deposition (IBAD) method under different temperatures and ion energies. Microstructure characterization by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning and transmission electron microscopy (SEM and TEM) confirmed that the nitride films were nanocrystalline in size and composed of grains with grain sizes ∼20 nm. Textures of the films were studied by XRD pole figure measurements. Residual stress was determined by the modified sin2ψ method using grazing incidence XRD. Hardness of the thin films was measured by nanoindentation. It is found that nanoindentation measurement cannot reflect the variation of residual stress. Nanohardness of the samples also displayed insignificant relationship with texture. Since the dislocation activity is retarded due to nanograin structure, the geometrical strengthening via texture control or Hall–Petch relationship is no longer applicable. Therefore, grain rotation or grain boundary sliding may be the deformation mechanisms for nanocrystalline thin film. The contradictory relationships between hardness and preferred orientation were also clarified.