Evaluation of Interfacial Fatigue Strength of Hard Coating by Using Repeated Laser Shock Adhesion Test

Abstract

Abstract This study aims to evaluate the adhesion strength and durability of hard coatings in a non-contact manner by using Laser Shock Adhesion Test (LaSAT). Both heat-treated and as-plated (non-heat-treated) Ni-P coatings deposited on carbon steel substrate by electroless plating method were prepared as specimens for this study. LaSAT uses strong elastic waves induced by pulsed laser irradiation in order to apply tensile stress to the coating/substrate interface so that interface delamination occurs. The out-of-plane displacement is also measured simultaneously by using a laser ultrasonic interferometer, and the interface delamination is detected by the change of the out-of-plane displacement waveform. Furthermore, computation of the elastic wave propagation using Finite Difference Time Domain (FDTD) is carried out to estimate the interfacial tensile stress. In addition, the adhesion durability is investigated by repetitive pulsed laser irradiation, and the relationship between the adhesion strength and the number of laser irradiation cycles until delamination was obtained. Finally, we discussed the effects of heat treatment on the adhesion strength and durability. This method of LaSAT is a quick measurement for the adhesion durability, and then it may shed some light on quality control of surface coating.