Surface Pretreatments Including Laser Texturing for Thermal Spraying

Abstract

Abstract Surface treatments are often necessary in thermal spraying to modify the surface properties of materials and then to improve the coating adherence. Several techniques exist. Among them, conventional techniques such as sandblasting, chemical degreasing and some others like high pressure water jet or laser ablation can be implemented. However, whatever the results, some drawbacks can always be listed according to the materials considered (sensitive materials, low adherence level). By this way, new techniques have to be developed. Considering the laser technology, some new treatments can be particularly suitable for surface modifications. Based on the printing technology, laser texturing implementing fiber laser technique combined with a scanner permits to engrave quickly uniform holes on the surface. Applied as a surface treatment before spraying step, the potential of such technique is particularly observed in this study. According to the laser parameters, several points can be analysed such as size (diameter and depth) and the distance between each holes. After surface characterizations by SEM observations and roughness measurements, adhesion tests were then implemented. Considering NiAl coatings sprayed on textured aluminium alloy substrates, some very interesting adherence results (55 MPa) were measured in comparison to the conventional treatments (45 MPa after degreasing and sandblasting) as well as laser ablation technique (34 MPa).