Coating debonding induced by confined laser shock interpreted in terms of shock wave propagation.

Debonding of coatings on a substrate is currently achieved by the so-called laser spallation technique. Here, we give an interpretation of the debonding by laser shock based on the impedance mismatch between the substrate and the coating rather than on the spallation process. An analysis in the (pressure-particle velocity) plane coupled with (space-time) diagrams provides the stress history at the interface and shows the possible traction history, depending on the applied pressure loading and the nature of the target. From this study, the different configurations that can lead to a separation of the layers under laser confined irradiation are evidenced according to the impedance mismatch between both components. A case of this analytical survey is experimentally studied. Free surface velocity measurements by the electro-magnetic technique are performed on a 75 mu m-thick aluminum coating stuck on a 1.5 mm-thick copper plate irradiated by various laser intensities in water confined geometry. A debonding threshold is observed on the records.