Laser adhesion test for thermal sprayed coatings on textured surface by laser

Abstract

The laser shock adhesion test (LASAT) is a technique allowing the generation of high tensile stresses in materials. The LASAT consists in focusing a pulsed laser beam on a water-confined target. The laser pulse crosses the water transparent layer and is absorbed by the target. High energetic plasma is created at the surface of the sample. As a response to the expansion of the plasma, a shock wave is generated and propagates through the sample. This shock wave leads to the generation of high tensile stresses in the sample. These stresses allow the interface solicitation in order to evaluate the dynamic adhesive bond strength of coated systems. In order to determine interface strengths, this technique has already proven its feasibility. In this paper, the adhesion strength of coated system was evaluated using LASAT for two surface pretreatments of substrates obtained by grit-blasting and laser surface texturing techniques. The generation of the high-intensity shock wave by laser plasma in the water-confinement regime has been performed at 7.1 ns at 532 nm with the new Nd:YAG laser facility HEPHAISTOS. This paper shows that surface treatments have a great influence on the adherence results of the coated systems obtained with laser adhesion test. However, the LASAT is efficient on thin coating. In that sense, thicker industrial coatings are not adapted for the conventional LASAT anymore. Therefore, a new technique was designed to improve and extend the conventional technique. This technique consists of varying the delay Δt between two incident pulses to adjust the location of the maximum tensile stresses near the interface. Some preliminary results on the improved configuration are presented in this paper and the problematic of the laser-matter interaction with two time-delayed laser pulses which has arisen is discussed.