Microstructure and mechanical properties of pressure-less sintered B4C–SiC–ZrB2–LaB6 ceramic composites

The effect of LaB₆ on the densification and microstructure of pressure-less sintered 0.4B₄C–0.4SiC–0.2ZrB₂ ternary ceramic with eutectic composition was investigated. The Vickers hardness, bending strength, and fracture toughness of the quaternary ceramic were discussed based on the microstructural characteristics. The densification of the 0.4B₄C–0.4SiC–0.2ZrB₂ ceramic was enhanced with increasing LaB₆ content from 0 to 70 mol% (the proportion to B₄C–SiC–ZrB₂). When the LaB₆ content was 50 mol%, the densification rate of the composite ceramic reached a peak. The 0.27B₄C–0.27SiC–0.13ZrB₂–0.33LaB₆ quaternary composite ceramic has reached a density of over 95% after being sintered at 2 100°C for 1 h. The B₄C and SiC phases had refined grains of 1–3 µm with intragranular structures in the as-sintered ceramics. The hardness and strength reached 17.9 ± .8 GPa and 307 ± 38 MPa, respectively. Crack deflection and branching were ascribed to the improved fracture toughness of 3.78 ± .26 MPa·m^1/2. This study provides new ideas for fabricating dense non-oxide ceramic composites with enhanced properties.