Microstructures, Properties and Fracture Behavior of Solidified TiC-TiB<sub>2</sub> Composites with Increasing Content of TiB<sub>2</sub>

Abstract

By adjusting the mole ratio of C and B elements in combustion system, solidified TiC-TiB2 composites with different TiB2 mole fraction were achieved by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that with increasing TiB2 content, the matrix of TiC-TiB2 composite ceramics transformed a number of fine TiB2 platelets from the TiC spherical grains, and fine-grained even ultrafine-grained microstructures were achieved in solidified TiC-50mol% TiB2 due to eutectic growth under rapid solidification of the ceramic. Properties showed that relative density, Vickers hardness and flexural strength of TiC-50mol%TiB2 simultaneously reached the maximum values of 21.5 ± 1.5 GPa and 860 ± 35 MPa , whereas TiC-66.7mol%TiB2 presented the maximum fracture toughness of 13.5 ± 1.5 MPa • m0.5. FESEM fractography analyses of the ceramics exhibited a mixed mode of transcrystalline fracture of TiC spherical grains and intercrystalline fracture of TiB2 platelets, and the tendency of intercrystalline fracture was obviously enhanced with increasing TiB2 content to be 66.7 mol%, resulting in enhanced toughening mechanisms of crack deflection, crack-bridging and pull-out by fine TiB2 platelets, thus, the highest flexural strength was achieved in TiC-50mol%TiB2 due to the achievements of both fine-grained microstructures and high fracture toughness in the full-density solidified ceramics.