Ceramics-Silikáty 51 (4) 181-189 (2007)

Improvement of mechanical properties of alumina and zirconia plasma sprayed coatings induced by laser POST-treatment

P. Ctibor, L. Kraus, J. Tuominen, P. Vuoristo, P. Chráska

Alumina and stabilized zirconia were plasma sprayed in air using a water-stabilized plasma torch. Nd-YAG laser was then used for additional treatment of the plasma sprayed coatings. The laser was maintained in a quasi-continual regime and defocused from the surface to increase the treated area. Energy density was varied together with the laser scanning velocity to ensure variance in thermal history of the treated surfaces. Microhardness, surface roughness and slurry abrasion resistance (SAR) were measured before and after the laser treatment. Results vary in dependence on the laser treatment parameters. When the laser treatment resulted in substantial changes of the structure (up to a complete re-melting of the surface), enhancement of all measured properties was proven. It is demonstrated that the change of the mechanical properties can be correlated with the optical properties of the coating materials at the laser wavelength. Microstructural aspects of the laser treatment are discussed as well, especially at the boundary between the laser-annealed layer and the basic coating. It is pointed out that laser remelting done by the use of a high energy density can cause presence of cracks, although the wear resis-tance as well as microhardness of the coatings is improved by this way. A cast ceramic material EucorTM with the composition ZrO₂–Al₂O₃–SiO₂ was treated by a diode laser utilizing the knowledge found on plasma coatings. The degree of improvement of the wear resistance, microhardness and homogeneity of microstructure was similar as in the case of plasma coatings.

Keywords: Plasma spraying, Laser post-treatment, Wear resistance, Al₂O₃, ZrO₂