Evaluation of Fracture Strength of TiN Thin Film on Cemented Carbide

Abstract

To evaluate the fracture strength of TiN thin films deposited on the hard metal substrate WC-Co, and to investigate the influence of the deposition conditions (bias voltage VB) on the fracture strength of TiN thin films, the sphere indentation test was carried out to determine the ring crack initiation strength σf,m in TiN thin films deposited on two kinds of WC-Co substrates differing in hardness using sphere indenters of varying diameter. TiN thin films 2.5 μm thick were deposited by dc magnetron sputtering under various VB. Based on the probabilistic theory assuming a two-parameter Weibull distribution, the averages of the fracture strength σ~f of TiN thin films without residual stress under conditions of uniform tensile stress and the residual stress σ~R of thin films were predicted from the distribution characteristics of σf,m. The main results were as follows: the average σ~f is almost independent of sphere indenter diameter and substrate hardness, and decreases with increasing VB; the variation in σ~f is mainly due to the grain size of thin films; the residual stress σ~R increases with increasing VB, and this tendency is qualitatively consistent with the measurements obtained by the X-ray diffraction method.