Effects of solids loading on microstructure and mechanical properties of HfB2–20 vol.% MoSi2 ultra high temperature ceramic composites through aqueous gelcasting route

HfB 2 –20   vol.% MoSi 2 ultra high temperature ceramic composites were prepared through aqueous gelcasting route. The stability of HfB 2 and MoSi 2 suspensions were studied by zeta potential measurements, sedimentation tests and apparent viscosity measurements. The solids loading had significant effects on the green and sintered densities, microstructure and mechanical properties of HfB 2 –MoSi 2 composites. The values of flexural strength of the green and sintered bodies ranged from 18.3 to 38.7, and 111.5 to 415.9   MPa, respectively, which were strongly dependent on the solids loading. The values of fracture toughness of the sintered bodies ranged from 2.18 to 4.24   MPa   m 1/2 . The highest relative density, mechanical properties and the most homogeneous microstructure was obtained when the solids loading was 45   vol.%. The highest green strength, flexural strength and fracture toughness were 38.7   ±   5.3   MPa, 415.9   ±   17.0   MPa and 4.24   ±   0.22   MPa   m 1/2 , respectively.