Microstructure and mechanical properties of in situ synthesized (TiB2 + TiC)/Ti3SiC2 composites

Based on thermodynamic analysis, highly dense (TiB2 + TiC)/Ti3SiC2 composite ceramics with different TiB2 volume contents were in situ fabricated in situ by hot-pressing at 1500 °C. Laminar Ti3SiC2 grains, columnar TiB2 grains and equiaxed TiC grains were clearly identified from microstructural observation; grain boundaries were clean. The increase of TiB2 volume content significantly restrains the grain growth of the Ti3SiC2 matrix. As the content of TiB2 increases from 5 vol.% to 20 vol.%, the bending strength and fracture toughness of the composites both increase and then decrease, whereas the Vickers hardness increases linearly from 6.13 GPa to 11.5 GPa. The composite with 10 vol.% TiB2 shows the optimized microstructure and optimal mechanical properties: 700 MPa for bending strength; 9.55 MPa m1/2 for fracture toughness. These are attributed to the synergistic action of strengthening and toughening mechanisms such as particulate reinforcement, crack deflection, grain's pull-out and fine-grain toughening, caused by the columnar TiB2 grains and equiaxed TiC grains.