Microstructure and properties of (SiC, TiB2)/B4C composites by reaction hot pressing

(SiC, TiB2)/B4C composites were fabricated by reactive hot-pressing B4C, Si3N4, α-SiC and TiC powders, with (Al2O3 + Y2O3) as sintering additives. According to the thermodynamics principles, the possible reaction equations and the reaction products for the system were determined. By means of XRD, SEM of surface thermally etched and TEM the phase composition was determined. It was shown that the phase composition of sintered body was B4C, α-SiC, BN and TiB2, and the matrix was B4C and α-SiC. The typical values of hardness, bending strength, fracture toughness and the relative density of the composites can reach HRA 88.6, 554 MPa, 5.6 MPa m1/2 and 95.6%, respectively. Furthermore, the microstructures of the composites were analyzed by TEM, SEM and energy spectrum methods. The results show the presence of laminated structure and a clubbed frame dispersion phase and bunchy dispersion phase among the matrix. Some intragranular structures were also found in the B4C grains. Microstructural analysis indicates that the new formed phase, uniform and fine grains, and the layered and clubbed structure play an important role in improving the properties of the composites. Fractography and crack propagation suggest that crack deflection and crack bridging are the possible toughening mechanisms.