A Laser Surface Texturation to Control the Coating-Substrate Interface Behaviour

Surface state takes an important role in particle bonding and formation of the first layer of coatings in thermal spraying. From a chemical aspect as well as a mechanical point of view, in all cases, the substrate surface needs to be as adapted as possible to promote the adhesion of the sprayed particles and then the coating. In order to control such parameters, several works are devoted to avoid disadvantages noticed for sensitive materials but also to optimize the surface preparation becoming more repeatable. This is particularly the aim of this study which consists in developing a laser surface texturation before the spraying process to improve the coating adherence. According to the laser parameters, different surface morphologies (hole diameters, surface roughness, hole depth, etc.) can be developed. A statistical model was then applied to highlight the main influent parameters promoting the coating adherence. The surface material morphologies were characterised by SEM and 3D profilometry. Bond strength was evaluated through ASTM C633 pull tests and interface indentation tests. This approach has been applied on the system Al 2017 / NiAl and demonstrates a high influence of the laser treatment. Among the substrate surface conditions, laser texturation yielded high bond strength (higher than the conventional degreased and sand-blasted preparation). Surface geometry has to be adjusted as a function of the holes morphology and particles size to improve the interface behaviour. The thermal effect induced during the laser-matter interaction has to be controlled to avoid negative effects of the substrate properties.