Microstructure transformation and mechanical properties of TiC-TiB2 ceramics prepared by combustion synthesis in high gravity field

By conducting combustion synthesis in high-gravity field, the solidified TiC-TiB2 with a series of TiB2 mole content were prepared through adjusting the mole ratio of C and B elements in combustion system. XRD, FESEM and EDS results showed that with increasing TiB2 mole 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-50%TiB2 due to the coupled quasi-eutectic growth under rapid solidification of the ceramic. Properties showed that relative density, Vickers hardness and flexural strength of TiC-50%TiB2 simultaneously reached the maximum values of 98.7%, 21.5 +/- 1.5 GPa and 860 +/- 35 MPa, whereas the maximum fracture toughness of 13.5 +/- 1.5 MPa m(0.5) was achieved in TiC-66.7%TiB2. FESEM fractography analyses of the solidified ceramics indicated that the highest flexural strength achieved in TiC-50%TiB2 benefits from not only the lowest content of Al2O3 inclusions and Cr-W-Ti borides, but also the achievements of fine-grained microstructure in the near-full-density ceramic and high fracture toughness contributed from a intensive coupled mechanism of crack deflection, crack-bridging and pull-out by a large number of fine TiB2 platelets. (C) 2012 Elsevier B.V. All rights reserved.