球圧子押込み試験によるTiN被覆超硬合金における薄膜の破壊靱性評価

概要

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The purpose of this study is to clarify the validity of the sphere indentation test method to evaluate the fracture toughness K_c of ceramic films deposited on the hard substrate, and to clarify the effect of bias voltages V_B on the fracture toughness K_c of ceramic films. TiN films were deposited onto three kinds of WC-Co substrates with different hardness using dc magnetron sputtering under various bias voltages V_B. Sphere indentation tests were carried out to determine the load for ring crack initiation P_f and the ring crack radius γ_f on TiN films using sphere indenters of varying diameter 2R. The fracture toughness K_c was calculated as the mode I stress intensity factor for a surface crack on TiN film using P_f and γ_f. The crack length c_i was assumed as the grain size of TiN films. The main conclusions are the following. (1) The residual stress δ_R of TiN thin films and the hardness H_u of thin films increase with increasing bias voltage V_B regardless of the substrate hardness. (2) Fracture toughness K_c decreased as increase in the diameter 2R in cases with a small 2R and gradually approached a constant value in cases with a large 2R. The K_c-2R relationships and the constant value of K_c are independent of substrate hardness. (3) Fracture toughness K_c increase as V_B is increased. That tendency is mainly due to the residual stress on TiN film.
2009-09-25