TEM analysis, mechanical characterization and oxidation resistance of a highly refractory ZrB2 composite

The microstructure of a dense ultra-high-temperature ceramic, namely ZrB2 containing 15 vol% of WSi2, was characterized by X-ray diffraction, scanning and transmission electron microscopy. ZrB2 displayed a core-shell structure: the core was constituted by the original MB2 grain and the shell by a (Zr,W)B-2 solid solution which grew epitaxially on the core. According to the final microstructure with mixed Zr, W-silicides, -borides and -carbides at the triple points and clean grain boundaries, a densification mechanism for ZrB2 in presence of WSi2 is proposed. This composite displayed excellent thermo-mechanical properties, like strength retention of 84% at 1500 degrees C in air and moderate oxidation up to 1650 degrees C. Correlation between microstructure and properties are here presented in relationship to other ultra-refractory ceramics available in the literature. (C) 2014 Elsevier B. V. All rights reserved.