Abstract: The green bodies of the HfB_2-(5%-15wt%) MoSi_2 ultra high temperature ceramics (UHTCs)system were produced by gel-casting when pH was 10.9, the content of dispersant（PMAA-NH_4）was 8vol% and the solid content of the slurry was 40vol%. the density of the green bodies had achieved above 4.25 g/cm~3 . They were sintered in a high multi-furnace under a flowing argon atmosphere at 1950 ℃ for 30 min. The effects of MoSi_2 additions on the properties of HfB_2 UHTCs were studied. The phase compositions were analyzed with an X-ray diffractometer and the microstructures of the sintered UHTCs were studied by SEM. The results show that the densification and the mechanical properties of the HfB_2 UHTCs added with the increase of MoSi_2 were improved highly. When 15wt% MoSi_2 were added, the hardness of the HfB_2 UHTCs reached 9.8 GPa, the bending strength reached 389.7 MPa and the fracture toughness reached 3.7 MPa·m~(1/2).

Key words: gel-casting%UHTCs%microstructure%mechanical properties