Evaluation of a pulsed laser technique for the estimation of the adhesion strength of oxide coatings onto metallic substrates

摘要

The aim of the present study was to investigate the possibility of using laser ultrasonic technique for the estimation of the adhesion of ceramic coatings, deposited onto metallic substrates by thermal spraying techniques. For this purpose, a pulsed Nd:YAG laser (λ=1064 nm, 14 ns) was used to irradiate Al_2O_3 coatings, of different thicknesses, deposited onto stainless steel substrates by atmospheric plasma spraying (APS). The so-generated acoustic waves were recorded in-situ using a laser heterodyne interferometer placed at the back surface of the metallic substrate. In order to correlate the so-obtained waveforms with the damage resulted in the bi-layered system, a physical and an analytical models have been developed. Moreover, the stress field developed at the coating/ substrate interface, due to the combined acoustic and thermo-mechanical effects, can be determined by numerical simulation, giving important information about the adhesion strength of transparent coatings deposited onto metallic substrates, by thermal spraying techniques.