Pressureless sintering and characterization of gel-cast ZrB2–SiC-based composites processed from optimized slurries

Abstract

Gel-casting followed by pressureless sintering has been developed as a process to fabricate near-net shaped ZrB₂-20 vol.% SiC composites. The slurries for gel-casting have been prepared by using novel environment-friendly additives, egg-white (containing albumin) as a binder and sucrose with polyacrylic acid (PAA) as a dispersant to control viscosity. The slurry composition has been optimized (35–38 vol.% solid loading, 22–26 vol.% egg-white, 4–8 vol.% sucrose, and 0.3 vol% PAA) to achieve a uniform dispersion of constituents at pH = 9 with minimum zeta potential and shear thinning behavior, as verified by rheological studies. Defect-free green bodies with relative density (RD) >50% and crushing strength ∼3.9–7.7 MPa, obtained by gel-casting of optimized slurries followed by controlled drying, have been sintered to attain RD ∼98%. Uniform and reduced shrinkage during drying or sintering ensured by optimum solid loading and a uniform dispersion of constituents, has restricted the formation of defects in the sintered products.