Abstract
Titanium nitride (TiN) thin films were deposited by the ion beam mixing (IBM) on the steel substrate. TiN thin films had a fiber texture with the fiber axis of <001> direction perpendicular to the film surface and the film thicknesses were 0.5, 1.0, 2.0, 4.0μm. These specimens were subjected to four point bending, and the stresses in films and substrates were measured by the X-ray diffraction method at each applied strain. In the examination, the films surface were replicated with cellulose acetate sheets at each applied strain and the replicated sheets were observed by scanning electron microscopy. The initial residual stress was equi-biaxial compression between -3.0, -2.7, -2.3, -0.9 GPa for the cases of 0.5, 1.0, 2.0 and 4.0μm, respectively. For thinner specimens, the rate of the increase of measured value of σ_<11> with the applied strain is lower than that of prediction, while for the film with 4.0μm the experimental value agrees well with the prediction. While the substrate is under uniaxial stresses, the film was in the biaxial state of stress because of the mismatch of Poisson's ratio. When the measured stress in the film exceeds a certain value, the stress departs from the linear relation and levels off. The onset of nonlinearity is slightly after the first appearance of cracks and the leveling of the stress was caused by multiple cracks in the film. The maximum stress measured in films increased with decreasing thickness.
