Cold spray process was chosen as a good candidate for dimensional restoration and protection of components. Commercially pure aluminum, aluminum-alloy or titanium were recommended for different applications. This paper investigates laser surface texturing association to enhance durability of sprayed coatings. Laser is easy automated, localized and reliable process. It was applied for prior-surface treatment. Textured surfaces were produced and compared to conventional treatments, such as grit-blasting, in terms of deposition efficiency and adhesion bond strength. Patterns promoted direct particle embedment. Particle-substrate interface exhibited significant temperature rate and strain in cavities. Intimate contacts and particle compressive states were assumed responsible for improvement. The particle deformation and bonding behaviors were evaluated and discussed for the different configurations. Thus, window of deposition was increased with laser surface texturing. Anchoring mechanisms increased two fold the adhesion strength compared to conventional pre-treatments. In one case, the interface was stronger than the coating cohesive strength.

Cold spraying consists in depositing a variety of metals as dense coatings onto metal surfaces. Indeed, copper, stainless steel, nickel, chromium, aluminum, cobalt, titanium, niobium and other metals can all be deposited, as well as metal alloys according to these base-metals and braze powders. The particle-substrate contact time, contact temperature and contact area upon impact are parameters influencing physico-chemical and mechanical bonds. The resultant bonding arose from plastic deformation and temperature at the interface which illustrates why metal coating cannot be sprayed onto rough ceramic substrates. Laser surface texturing has been used as prior treatment to create specific topography. Metal-ceramic has demonstrated a non-deformation of the substrate minimizing intimate bonds. Particle compressive states indicate anchoring mechanisms for laser textured surfaces. Consequently, cold spraying parameters depend on the target material and a methodology can be established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Mechanical adhesion is a key issue in cold spray process. As a result, laser surface texturing is a promising tool to adapt the surface to improve adhesion. Metallization process can be achieved.

Cold spraying is particularly suitable for elaborating heat and oxidation sensitive coatings. Due to the fact that the particles are not melted during the spraying process, it is thus possible to elaborate coatings without chemical modifications. Nevertheless, according to the materials considered, some interface defects can be detected inducing an inadequate adhesion between the substrate and the coating. Bonding mechanisms are not only strongly dependent on the particle velocity but also on the state of the surfaces. By this way, surface pre-treatments can be necessary to improve adhesion. From all the surface modification technologies, laser ablation process is very interesting due to its flexibility by using optical fibers and due to the perfect control over the treated area. It is then possible to interact with the material during all the spraying process on the substrate surface as well as on the interface layers. This is particularly the aim of this study which consists in exploring the laser influence, implementing the PROTAL process, on the different interfaces quality for coatings elaborated by cold spray on metallic substrates. By controlling the chemical composition of the materials, the coating cohesion as well as the adhesion level, coatings were sprayed on pure titanium and titanium and nickel based alloy substrates.

In this study, Ni-Al powder is plasma sprayed on various substrates prepared by in-situ laser ablation and preheating. Surface topography and splat shape are examined in order to assess how laser induced heat flux affects surface modifications and variations in splat shape. The causes of laser induced surface modifications are identified for Al, Ti, and stainless steel substrates and it is shown that laser preheating improves surface absorptivity, which effectively subjects more defects to the effects of the laser.

To avoid the constraints due to the conventional surface preparation before thermal spraying (degreasing and sand-blasting), the PROTAL process was developed implementing a Q-Switched Nd:YAG laser with a very short pulse duration to prepare the surface simultaneously to the coating buildup. Until now interesting results were obtained both from the adhesion and economical points of view. Specific parameters were developed according to the spraying process (APS, HVOF, wire arc), the powder (Cu alloy, Al 2 O 3 , WC-Co, ...) as well as the part nature (Ni alloy, Magnesium, steel, aluminium alloys, etc.). Considering the wide development of thermal spray applications in the automotive industry, new developments of the PROTAL process were considered in order to reach the feasibility of an internal laser treatment of the parts. After a presentation of the implementation of a new laser head in the thermal spray environment, some results concerning the case of a metallic coating (ferrous alloy) on a metallic part (aluminium alloy) will be presented.

The flattening behavior of individual splats plays a fundamental role in the elaboration of thermal spray coatings. In the PROTAL process, an in-situ laser treatment is coupled with spraying operations. It was shown that a pulsed laser irradiation can effectively suppress the splashing phenomenon of splats. This aspect was primarily attributed to the efficient removal of surface adsorbates/condensates. But, it may also be enhanced by the modification of the surface topography that improves the surface wettability. Therefore, this study deals with the effects of the surface microroughness modifications on the surface wettability induced by the PROTAL process. Several roughness parameters characterizing the surface topography are also discussed from a static wettability point of view.