Excimer laser-induced microstructural changes of alumina and silicon carbide

Surface treatments with a KrF excimer laser were applied on alumina and sil icon carbide ceramic materials. Results on the surface modifications induce d by laser were related to the processing parameters: laser fluence (1.8 an d 7.5 J/cm(2)), number of laser pulses (1 to 500), frequency (1 to 120 Hz), pulse duration (25 ns), sample speed under the laser beam and working atmo sphere. It was ascertained that alumina can be laser treated under air, whi le silicon carbide needs an inert atmosphere to avoid surface oxidation. Mi crostructural analyses of surface and cross section of the laser processed samples evidenced that at low fluence (1.8 J/cm(2)) the surface of both cer amics is covered by a scale due to melting/resolidification. At high fluenc e (7.5 J/cm(2)) there are no continuous scales on the surfaces; material is removed by decomposition/vaporisation and the depth of material removal is linearly dependent on the number of pulses. On alumina surface, a network of microcracks formed, while on silicon carbide different morphologies (fla t and rugged areas, deposits of debris and discontinuous thin remelted scal es) were detected. The evolution of surface morphology and roughness is dis cussed with reference to composition, microstructure and physical and optic al properties of the two tested ceramics and to laser processing parameters . (C) 2000 Kluwer Academic Publishers.