Abstract
Alumina-titania coatings deposited by air plasma spraying (APS) are widely used to protect components against wear at low temperatures. It is known that microstructures formed by the post-laser remelting of as-sprayed coatings exhibit a densification but also numerous macrocracks due to the rapid cooling and thermal stresses. By using the laser-assisted air plasma spraying (LAAPS), the laser beam interacts simultaneously with the plasma torch in order to increase coating surface temperature and possibly superficially remelt the coating. As a result, the microstructure is partially densified and macrocracks, which are generally produced in the post-laser irradiation treatment, can be inhibited. In addition, this hybrid spraying can be done without the post-treatment of coating. In this paper, LAAPS was performed to improve the mechanical properties of Al2O3-13%TiO2 coatings. The coating microstructure was characterized by SEM and X-ray diffraction. The mechanical characterization was done by hardness measurements, erosive wear tests and abrasion wear tests. Results showed that laser assistance may induce: (1) the disappearance of vertical and horizontal macrocracks due the laser irradiation in the coatings for a laser irradiation density lower than 34 W.mm-2, (2) an important decrease of the amount of microcracks in the deposited splats, (3) the partial transformation of the metastable γ-Al2O3 phase in the equilibrium α-Al2O3 phase, (4) a hardness increase of 11%, (5) an improvement of the erosive wear resistance by 12% and (6) an improvement of the abrasive wear resistance by 38%.
