Abstract: Nano-sized SiC reinforced B₄C matrix composites were fabricated through a pyrolysis route from polycarbosilane(PCS) precursor. The microstructure and
properties of the materials, compared with the materials sintered by direct mixed powders, were investigated. It shows that, the composites fabricated via precursor
form a kind of complicated intra-intergranular structure: nano SiC within the grains of B₄C and Al₂O₃, sharp angle-layered SiC precipitating in the grain
boundaries, and SiC substructures within the grains of B₄C. The crack deflection within the crystal grains is caused by intragranular fracture, increasing the
fracture toughness significantly. The homogenization, relative density and mechanical properties of the composites fabricated by polycarbosilane precursor are higher
than those of the composites made by directly mixed powders.

Key words: boron carbide, polycarbosilane, precursor, nano SiC