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Influence of Laser Surface Cleaning Combined with Substrate Laser Preheating on Thermal Spray Coating Adhesion
S. Costil, H. Liao, O. Chretien, A Loredo, A. Gammoudi, M. Verdier and C. Coddet

In thermal spraying, the morphology of sprayed splat raises the coatings adhesion and the properties which are determined by the spraying parameters. Many studies in this field show that the substrate surface temperature as well as cleaning the substrate are two very relevant factors for the splat shape. The hypotheses of substrate surface wettability and contamination or absorption layer on the surfaces are supported by the fact that the near disk-shaped splat can be obtained by increasing the substrate temperature. For cleaning operations, despite all conventional techniques (solvents), laser ablation is powerful enough to eliminate the contaminants on the substrate surface just before powder spraying. Concerning surface heating, laser irradiation can control the treated area and then the oxidation in comparison with the flame technology. In order to understand these effects, an analysis of NiAl splat morphology on a polished TA6V substrate was carried out. Results show that the critical temperature above which the disk shaped splat is formed can be decreased dramatically by laser ablation. Moreover, laser ablation combined with another laser increased the adhesion strength of the coatings.

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