The effect of heat-treatment temperature on structure and properties of TiB2/C composites Original Research Article

Mesocarbon microbeads are an excellent precursor for carbon materials, because of their ability to self-sinter. TiB2/C composites were prepared from mesocarbon microbeads with TiB2 additions by pressureless sintering. The effect of heat treatment temperature on microstructure and fracture behavior of the products was investigated. Liquid formation and resultant layered structures were observed when the composite was heat treated at 2800 K or above. Low levels of TiB2 (5 vol%) addition improved the fracture toughness. At these levels the catalytic effect on graphitization was low and the size of TiB2 particles decreased significantly because of their interaction with the mesocarbon microbeads. When the content of TiB2 in the composite was 20% by volume, the mesophase carbon was transformed completely into graphite under the influence of a eutectic liquid, as shown by XRD analysis and fractography, which led to a dramatic decrease in fracture toughness. XRD analysis and laser ablation ICP-MS indicate that boron diffused into the carbon matrix when composites were heat treated above 2700 K. Resistance of the composite materials to crack propagation increased further when finer TiB2 particles were used, and eventually, TiB2/C composites with fracture toughness as high as 1.92 MPa m0.5 were obtained.