Evaluation of Fracture Toughness of TiN Thin Film on Cemented Carbide by the Sphere Indentation Testing

Abstract

The purpose of this study is tQ clarify the validity of the sphere indentatiQn test method to evaluate the fracture toughness Kc of ceramic fil π ls deposited on the hard substrate ， and to clarify the effect of bias voltages 玲 orl the fracture t ughness K ⊂ of ceramic 丘 lms ． TiN 行1ms were deposited onto three kinds of WC − Co substrates with different hardness using dc rnagr ユ etrQn sputtering urlder various bias vo ］ tages VH． Sphere indentation tes亡s were carried ou 亡 to determine the load for rillg crack initiation Pf and the ring crack radius rf on TiN films using sphere indenters of varying diameter 2R ． The fracture toughness Kc was calculated as the mode I stress intensity factor for a surface crack on TiN nlrn usirlg Pt and rr ， The crack length cs was assumed as the grainsize ofTiN films ． The main conclusions are the following ．(1) The residua1 stress σR f TiN thin 田 ms and the hardness 伍 of thin 丘lms increase wlth increasing bias voItage Vn regardless of the substrate hardness．(2) Fracture toughness κ c decreased as illcrease 亘 n the diameter 2R in cases "with a small 2ム-and gradually approached a constallt value i［l cases with a large 2R ． The κ c − 2R relationships and the constant value of ノ (c aTe independen 亡 of substrate hardness． (3) Fracture toughness 1(c increase as Us is increased ． That tendency is mainly due to the residual stress on TiN mm ．