Mechanical characterization of optical TiO2-SiO2 coatings with different microcolumnar structures
Tutor / director / evaluatorRoa Rovira, Joan Josep
Document typeMaster thesis (pre-Bologna period)
Rights accessOpen Access
New functional coatings for optical applications have an increasing complexity in their microstructure. TiO2-SiO2 coatings are being produced with tilted, zig-zaged, and curled columns in order to achieve different optical properties. However, the mechanical properties of these coatings and the influence of the different microstructural features are not known. Mechanical properties are key parameter to assure the structural integrity and reliability of the components. In this project, the evaluation of the mechanical properties and the damage mechanisms in terms of different growth structure (tilted, zig-zaged or spiral) and growth angle (70º or 85º) has been studied. To accomplish it, mechanical characterization at micro- and nanometric length scale by means of nanoindentation and nanoscratch tests have been made. The superficial damage induced using a sharp indenter was studied by using confocal laser scanning microscopy, atomic force microscopy and field emission scanning electron microscopy. Moreover, the sub-superficial damage as well as the adhesive and/or cohesive failure between coating and substrate was studied by focused ion beam. Results show that the main parameter controlling the mechanical response is the glancing angle. Coating architecture and number of layers have only a minor effect on the mechanical response. Low angle coatings present higher resistance to scratch testing than high angle coatings, but they show a brittle failure behavior.