Effects of a hierarchical macroporous–mesoporous structure with a low porosity porous ceramic preform on mechanical properties and Si particle refinement of RBBC composites

Abstract

In this study, a hierarchical macroporous–mesoporous structure B4C/C preform was prepared via gel-casting, using which the pore structure, as well as the B4C slurry stability, could be adjusted by using B4C powders with varying multimodal particle size distributions. The coarse, medium, and fine particle distributions of the B4C powders, and their effects on mechanical properties of the RBBC composites obtained by liquid Si infiltration were investigated. The results showed that the lowest B4C slurry viscosity and the densest B4C/C preform were obtained at a 6:1:3 ratio of coarse, medium, and fine particles. The Vickers hardness, fracture toughness, and flexural strength of the RBBC composites reached 21 ± 3 GPa, 4.09 ± 0.17 MPa m1/2, and 299 ± 17 MPa, respectively. Furthermore, the lowest residual Si content was 7.22 vol%, and fine residual Si phases had a toughening effect owing to their internal compressive stress.