Strength and Fracture Mechanism of Vapor Deposition Films Estimated by the Analysis of Three Dimensional Radiation Pattern of Elastic Wave

Abstract

A new system for analyzing the three dimensional radiation pattern of elastic waves was developed and applied to evaluate the mechanical characteristics of the TiN film deposited on the stainless steel by the hollow cathode discharge method. The system consists of four highly sensitive small sensors to measure both the arrival time and the amplitude of the P-waves, and a computer algorithm to fit the measured data to the two-dimensional profile locus of the P-wave amplitude for an assumed fracture model, The fracture mode estimated by the developed system was compared with the results obtained by both the source wave analysis and the microscopic observation. It was found that the TiN film (4μm thickness, double layered) under the compressive loading suffered various damages according to the following sequence. (1) At the elastic stress level, vertical cracks along the periphery of the splashed particles parallel to the loading direction were induced by the Mode-I fracture. This cracking is limited in the outer TiN layer, and therefore the substrate metal is isolated from the external environment. (2) At plastic strain of around 0.8%, Mode-I fracture along the boundary between the substrate and the TiN film was observed. This fracture was induced by emergence of slip steps in the substrate which was still isolated from the external environment. (3) At large plastic strain of 1.25%, the TiN film itself suffered the Mode-I fracture which was also associated with the slip step. The developed system was useful to elucidate the various fracture modes in or under the coated film.