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 0.4B(4)C-0.4SiC-0.2ZrB(2) 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 0.4B(4)C-0.4SiC-0.2ZrB(2) 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 0.27B(4)C-0.27SiC-0.13ZrB(2)-0.33LaB(6) quaternary composite ceramic has reached a density of over 95% after being sintered at 2 100 degrees C for 1 h. The B4C and SiC phases had refined grains of 1-3 mu m 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<middle dot>m(1/2). This study provides new ideas for fabricating dense non-oxide ceramic composites with enhanced properties.