Gelcasting of complex-shaped ZrB₂-SiC ultra high temperature ceramic components

Complex-shaped ZrB₂-SiC ultra high temperature ceramic components were successfully fabricated by gelcasting technique and pressureless sintering. When 0.4wt% poly(acrylic acid) (PAA) was used as dispersant and the pH value was 10, an aqueous ZrB₂-SiC-B₄C-C slurry with a high solid loading up to 50vol% but low viscosity (3.1Pas at 60s^-1) was prepared. For gelcasting process, the suitable monomers content (AM and MBAM) and the mass ratio of monomers (AM/MBAM) were selected as 3wt% and 15:1, respectively. After pressureless sintering at 2100°C for 2h, ZrB₂-SiC ceramics (using B₄C and C as sintering additives) finally achieved about 98% density. Investigation of the mechanical properties revealed a flexural strength of 405±27MPa and a fracture toughness of 4.3±0.3MPam^1/2. Complex-shaped ZrB₂-SiC ceramic components with homogeneous microstructure were also successfully produced. This study confirms that gelcasting is a reliable process for the fabricating of complex-shaped ultra high temperature ceramic components with satisfied properties.