Effects of silicon addition on the microstructure and properties of B4C-SiC composite prepared with polycarbosilane-coated B4C powder

Dense, fine grained B4C-SiC composites were successfully fabricated with the hot-pressing pyrolyzed mixtures of polycarbosilane-coated B4C powder and the Si additive at 1950 °C for 1 h under 30 MPa. The addition of Si not only improved the densification process due to the formation of liquid phase Si, but also greatly enhanced the mechanical properties of B4C ceramics. However, the added Si showed no significant effect on fracture toughness. The improvement in mechanical properties was attributed to the decrease of porosity and the elimination of free carbon derived from polycarbosilane and B4C powder. The introduction of Si improved the microstructure homogeneity and further refined the layer structure of in-situ SiC grains. The flexural strength, Vickers hardness, and fracture toughness of the sample prepared with 11.4 wt% Si, respectively, reached 389 MPa, 33.2 GPa, and 5.64 MPa m1/2.