Mechanische Eigenschaften transparenter Keramik im Vergleich mit gehärteten und ungehärteten Gläsern

The development work within this EU-funded EFRE project of the state of North Rhine-Westphalia was focused on a new generation of high-strength and extremely hard transparent ceramic materials and composites. These were implemented, tested and evaluated as a subtask in existing protective panel systems as a cover for sensors. In this way, the material development was oriented directly to the application and it was possible to make reliable statements, in particular with regard to fracture statistics and the survival probability, through extensive characterization of the materials and the composites. The main focus was on the polycrystalline magnesium aluminate spinel with the trade name Perlucor®, which was produced and further developed by the project partner. A second transparent ceramic in the form of an alpha aluminum oxide was compared with typical commercially available transparent materials such as polycarbonate as well as hardened and unhardened glasses. Like the well-known Gorilla Glass® from Corning, which is installed in most smartphones today, a standardized float glass as well as B270®, N-BK7® and Borofloat® from Schott. In addition, the effect of a thin, even more wear-resistant γ-Al2O3 coating on the spinel ceramic was considered. As a basic characterization, the Young´s modulus, the hardness, the fracture tough-ness and the flexural strength of all materials were examined and compared in detail. Additionally, the subcritical crack growth and creep behavior were determined for the focus material spinel and a statistical failure probability was calculated in the form of a stress-probability-time diagram. In addition to the mechanical properties, wear resistance was also experimentally investigated in load tests such as sandblasting tests and ball drop tests. The mass loss and the transmission loss were measured and an optical comparison was used. Fractographic examinations using light and electron microscopy were carried out in order to identify the break-causing defects. On the basis of the previously determined properties of the individual materials, laminates consisting of a 550 μm thick spinel top layer, 10 μm organic glue and various 1.8 - 2 mm thick glass or plastic substrates were produced. These were tested in further ring-on-ring bending tests in two different test setups. The results were evaluated and the best material combinations were identified with regard to application-related use