TiN被覆超硬合金における薄膜の破壊強度評価

概要

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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 V_B. Sphere indentation tests were carried out to obtain the micro fracture strength σ_<f,m> for ring crack initiation on TiN films using sphere indenters of varying diameter 2R. The main conclusions are the following. (1) σ_<f,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 σ_<f,m> and 2R can be predicted. (2) σ_<f,m> increase as V_B is increased. (3) Based on the probabilistic theory, the residual stress σ_R on TiN films and the fracture strength σ_f, of TiN films under uniform tensile stress condition for various V_B were estimated from the distribution characteristics of σ_<f,m>. Variation tendency in σ_R is consistent with that by X-ray stress measurement. But, variation tendency in σ_f is opposite to that in σ_<f,m>.
2006-08-25