Characterization of Ultra-high Temperature Ceramics via Transmission Electron Microscopy - ZrB 2 composites containing Tyranno SA3 SiC fibers: data collection -

The materials described in the present report were produced aiming at improving the fracture toughness of ZrB 2 ceramics, through the introduction of Tyranno SA3 SiC short fibers. Different kinds of sintering additives were chosen for the densification of the boride, namely ZrSi 2 , Si 3 N 4 and TaSi 2 . For each composition various sintering cycles were tested to identify the best temperature allowing densification of the matrix and minimize the fiber degradation. All the materials produced were examined through scanning electron microscope (SEM), to study the distribution of the secondary phases, and transmission electron microscope (TEM), to analyse the microstructure at nanoscale level, with particular attention to the evolution of the fiber morphology and to the study of the interfaces with the matrix in high resolution mode. This preliminary study allowed a first understanding of the chemical stability of Tyranno SA3 fibers towards different sintering additives and the ZrB 2 matrix. Varying the sintering temperature it has been also possible to evaluate how the fiber crystallites changes with the temperature and the additive. The mechanisms leading to the final microstructure, mechanical properties evaluation and correlation to the microstructural features will be discussed in the final report (December 2013).