Pressureless sintering of high-density ZrB2-SiC ceramic composites

Ultra-high-temperature ceramic composites of ZrB2 20 wt%SiC were pressureless sintered under an argon atmosphere. The starting ZrB2 powder was synthesized via the sol-gel method with a small crystallite size and a large specific surface area. Dry-pressed compacts using 4 wt% Mo as a sintering aid can be pressureless sintered to similar to 97.7% theoretical density at 2250 degrees C for 2 h. Vickers hardness and fracture toughness of the sintered ceramic composites were 14.82 +/- 0.25 GPa and 5.39 +/- 0.13 MPa.m(1/2), respectively. In addition to the good sinterability of the ZrB2 powders, X-ray diffraction and scanning electron microscopy results showed that Mo formed a solid solution with ZrB2, which was believed to be beneficial for the densification process.