Evaluation of fracture strength of TIN thin film on cemented carbide

Abstract

The purpose of this study is to absolutely evaluate the fracture strength of ceramic films deposited on the hard substrate by considering the residual stress on films, and to clarify the effect of the deposition condition on the fracture strength of ceramic films. TiN films were deposited onto two kinds of WC-Co substrates with different hardness using dc magnetron sputtering using various bias voltages VB. Sphere indentation tests were carried out to obtain the micro fracture strength σt.m for ring crack initiation on TiN films using sphere indenters of varying diameter 1R, The main conclusions are the following. (1) σt,m depend on 2R, but are independent of the hardness of a substrate. Based on the probabilistic theory assuming a Weibull distribution, the relationship between the mean value of σt,m and 2R can be predicted. (2) σt,m increase as VB is increased. (3) Based on the probabilistic theory, the residual stress σ̃R on TiN films and the fracture strength Sigma;̃f of TiN films under uniform tensile stress condition for various Vs were estimated from the distribution characteristics of σtild;R. Variation tendency in Su is consistent with that by X-ray stress measurement. But, variation tendency in Si is opposite to that in σt,m.