A high strength alumina-silicon carbide-boron carbide triplex ceramic

A ceramic particulate composite composed of oxide, and carbide ceramics was found to have high strength, hardness, and fracture toughness values. A composition consisting of Al2O3 with 15 vol% SiC and 15 vol% B4C additions was produced by hot-pressing at 1650 °C for 30 min, with full density reached after ~5 min at temperature. Both WB and WB2 were observed, with the W source presumably an impurity from WC milling media, and Al18B4O33 was also detected following densification. Strength was ~880 MPa, which is greater than values reported for comparable composites of Al2O3 containing 30 vol% SiC or B4C. Vickers hardness was ~21 GPa, and fracture toughness was ~4.5 MPa m½, comparable to values reported for the binary mixtures. The calculated critical flaw size of the material was similar to the size of the SiC/B4C clusters and microcracking at grain boundaries. The latter resulting from thermal expansion mismatch between the Al2O3 matrix and SiC/B4C reinforcing phases.