Fracture behavior of brittle thin coating

Abstract

In this research, the adhesion strength of PVD TiN film film on ceramics was investigated. In order to explore the failure source of TiN film, two kinds of transparent model substrate were chosen. Based on the results of model experiments, TiN coated $Si_3N_4$ was studied in the context of effect of substrate yield properties on the adhesion strength of TiN film. In chapter III, the failure mode of PVD TiN film on $(11\bar{2}0)$ sapphire were investigated by analyzing the adhesion strength and failure mechanism through in-situ observations of the fracture sequence during scratch tests and static normal indentation. TiN was deposited by arc ion plating on $(11\bar{2}0)$ sapphire and the thickness of the TiN film was controlled to 700 nm. Delamination of TiN film was monitored in-situ from below the contact through a transparent sapphire substrate, using zoom optics mounted into a video imaging sensor. In-situ observation of failure source enables us to detect the failure origin of TiN coating on sapphire. The failure origin of TiN film on $(11\bar{2}0)$ sapphire was identified as both rhombohedral and basal twinning of the sapphire substrate. Rhombohedral twinning was initiated first and basal twinning ensued. Twinning-induced plastic deformation of the sapphire substrate triggered the initiation of interfacial delamination of the TiN coating. The plastic deformation of the substrate ultimately induced failure of the protective coating. In chapter IV, TiN film coated soda-lime glass were investigated. The effect of TiN film thickness as well as the effect of elastic mismatch between TiN film and a soda-lime glass was analyzed. Similar to a sapphire substrate, through in-situ observations of the fracture sequence during scratch tests and static normal indentations, failure mechanism was suggested. TiN was deposited by arc ion plating on soda-lime glass substrate and the thickness of TiN film was controlled from 1 ㎛ to 5 ㎛. Sets of static normal indentations a...