High-Hardness Solidified TiB<sub>2</sub>-TiC Composites Prepared by Combustion Synthesis under High Gravity

Abstract

Large-bulk TiB2-TiC composite ceramics were prepared by combustion synthesis under high gravity. XRD, SEM and EDS results showed TiB2-TiC composites were mainly composed of the fine-grained microstructures of TiC matrix in which a large number of the fine TiB2 platelet grains were dispersed uniformly, whereas there discontinuously dispersed the ε-carbides with the enrichment of Ti atoms, and a few of isolated, irregular α-Al2O3 grains and Al2O3-ZrO2 colonies were also observed at the boundaries of the eutectic microstructures. The results of properties indicate that with increasing mass fraction of B4C+Ti+C in combustion systems, the relative density and fracture toughness of TiB2-TiC composites are all among 97%~99% and 6.5~7.1 MPa·m1/2, respectively, and the Vickers hardness and flexural strength are increased gradually to the maximum values of 28.6GPa and 615MPa, respectively. The achievement of full-density TiB2-TiC composites benefited from the design of full-liquid SHS products and the introduction of high-gravity field, and high hardness of the composite ceramics resulted from the absence of intermediate borides and the achievement of stoichiometric TiC phases due to rapid solidification, whereas high flexural strength of the composite ceramics benefited from the homogenization and refinement of the microstructures due to the rapid separation of the liquid oxides and the rapid coupled growth of TiB2-TiC.