Evaluation of Interfacial Strength and Delamination Detection of Plating Films by using Laser-induced Ultrasonic Waves

Abstract

This study aims to evaluate interfacial strength of surface coating by using laser induced ultrasonic wave. In this method, pulse laser beam is irradiated on the back surface of substrate, inducing strong elastic wave which propagates through the specimen thickness, and reflects at the top surface of the coating. The wave propagation and reflection generates an expansion wave (tensile stress), leading to the interfacial fracture (i.e. delamination). This is called laser spallation technique. This study changes the energy level of laser irradiation variously, and measures the coating delamination in-situ based on the out-of-plane displacement waveforms. The delamination can be detected by using correlation coefficient calculated with a series of the waveform obtained at epicenter of laser irradiation. The delamination can also be visualized by using laser ultrasonic wave scanning. In parallel, the computation of elastic wave is carried out using FDTD (finite difference time domain) and the interfacial strength is estimated quantitatively.