Compressive strength degradation in ZrB2-based ultra-high temperature ceramic composites

• Published in: Journal of the European Ceramic Society Vol. 31; no. 7; pp. 1345 - 1352
• Main Authors: Ramirez-Rico, J, Bautista, M A, Martinez-Fernandez, J, Singh, M
• Format: Journal Article
• Language: English
• Published: 01.06.2011
• Subjects: Ceramics; Compressive strength; Degradation; Mechanical properties; Oxidation resistance; Reduction; Silicon carbide; Strength
• ISSN: 0955-2219
• DOI: 10.1016/j.jeurceramsoc.2010.05.020

The high temperature compressive strength of ZrB2-SiC particulate composites containing either carbon powder or SCS-9a silicon carbide fibres was evaluated in air. Constant strain rate compression tests were performed on these materials at room temperature, 1400, and 1550 C. The degradation of the mechanical properties as a result of atmospheric air exposure at high temperatures was also studied as a function of exposure time. The ZrB2-SiC material showed excellent strength of 3.1 plus or minus 0.2 GPa at room temperature and 0.9 plus or minus 0.1 GPa at 1400 C when external defects were eliminated by surface finishing. The presence of C was detrimental to the compressive strength of the ZrB2-SiC-C material, as carbon burned out at high temperatures in air. As-fabricated SCS-9a SiC fibre-reinforced ZrB2-SiC composites contained matrix microcracking due to residual thermal stresses, and showed poor mechanical properties and oxidation resistance. After exposure to air at high temperatures an external SiO2 layer was formed, beneath which ZrB2 oxidised to ZrO2. A significant reduction in room temperature strength occurred after 16-24 h of exposure to air at 1400 C for the ZrB2-SiC material, while for the ZrB2-SiC-C composition this reduction was observed after < 16 h. The thickness of the oxide layer was measured as a function of exposure time and temperature and the details of the oxidation processes are discussed.