The Research On Thermal Shock Resistance Of ZrB₂ Based Ceramic Composites

The characteristics of advanced ultra-high temperature ceramics (UHTCs), such as strength at high temperature and oxidation resistance, allow them to be used in extreme environments including those associated with hypersonic flight, atmospheric re-entry, and rocket propulsion. ZrB₂+20vol%SiC, ZrB₂+25vol%SiC, ZrB₂+30vol%SiC and ZrB₂+20vol%SiC+20vol%ZrC composites were prepared by hot-pressing with vacuum. The microstructures and phase constitutions of the composites were investigated by the means SEM, EDS etc.. Mechanical properties of the composites were tested. The thermal shock behaviors of the selected materials was analyzed and observed at high temperature from room temperature to 2500℃.The flexural strength and fracture toughness of ZrB₂/SiC/ZrC composite which were produced successfully:ZrB₂+20vol%SiC are 470MPa and 5.21 MPa?m 1/2 ,ZrB₂+25vol%SiC are 520MPa and 5.26MPa?m 1/2, ZrB₂+30vol%SiC 672MPa and 5.32MPa·m^1/2 and ZrB₂+20vol%SiC+20vol%ZrC ceramic are 702MPa and 5.22 MPa·m^1/2 respectively. For the ZrB₂ based composites, with the addition of SiC particles, the excessive growth of ZrB₂ materials is restricted and grain structure is refined. Meanwhile the fracture modes are changed, namely, from transcrystalline to mixed transcrystalline/ intercrystalline. For the ZrB₂/SiC ceramic, strengthening mechanisms is grain refining and the toughening mechanism is crack deflection/decomposition and grain refining. The strength of ZrB₂/SiC materials are further improved by addition of 20vol%ZrC, because of the chemical consistency between the crystal (001) of ZrB₂ and the crystal (110) of ZrC. The addition of ZrC improved the sintering and mechanical properties of ZrB₂/SiC composite effectively.The simulation of thermal shock showed that there was compression stress in the middle of sample, and tension stress at the edge of sample. Results of thermal shock in the temperature range from room temperature to 2500℃indicated that of ZrB₂+30vol%SiC is the best. The addition of ZrC improved the sintering and mechanical properties of ZrB₂/SiC composite, but didn't show excellent thermal shock resistance. The heating processing increased thermal...