Reaction Sintering Of Porous Of Tib <sub> 2 </ Sub>-tic Composite Ceramics

Boride ceramics have some special properties, such as high melting points, high hardness, high heat conductivity, low-expansion coefficient, excellent corrosion resistance and high electrical conductivity. And the boride materials have great potential to be used as high temperature filter materials. It is innovative to investigate the boride materials, especially, formation boride materials by in-situ synthesis technicalIn this paper, porous TB2-TiC composites are fabricated with Ti, B4C and carbon black powder by in situ synthesis under vacuum sintering. Effect of powder size, mol ratio of Ti, B4C and carbon black, sintering temperature and dwell time on the sintering properties, pore-size distribution and mechanical properties are investigated. Phase, pore morphology of porous TiB2-TiC composites are investigated by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results on their properties of densities, three-point bend strength and gas permeability show that porous TiB2-TiC composites have good performances by in-situ synthesis under vacuum sintering. The results are as follows:1.3Ti-B4C systems have intermediate phases TiB and Ti3B4 when temperature below 1300℃, with the sintering temperature rise, the intermediate phases disappeared, only have TiB2 and TiC phases.2. The TiB2-TiC composites by in-situ synthesis under vacuum sintering are connectivity and well distribution, the range of aperture distribution is incomprehensive. During the crack propagation, when the crack encounters the small TiB2 grains area, the crack propagation path is border-grain because of its high strength and modulus, and the fracture faces are very coarse; when it encounters the bulky grains, the fracture patterns in some bulky TiB2 grains area are cross-grain fracture, and the fracture faces are very smooth, sometimes some steps are found in fracture face. In general, the fracture model are mix fracture model which include cross-grain fracture and transcrystalline fracture.3. The results on the mechanical properties show that effects of powder size on the density and mechanical properties of sintered samples are very large. In a same system, the density, bending strength of the samples sintered at higher temperature are higher than these of the samples sintered at low temperature. Under a same sintered temperature, the density and bending strength with 3Ti-B4C system is higher than that with 4Ti-B4C-C systems. From the experiment, we may conclude that B4C particle size grain distribution has an important effect on the density and mechanical properties of sintered samples.4. Using the Ti-B-C ternary stable phase diagram and thermodynamic dates of some known materials at 1700℃, the unknown thermodynamic dates of some materials of this system were estimated. According to the conditions of thermodynamics phase equilibrium, it is calculated about the stabilized chemical potential of the Ti-B-C ternary system. It is one of theoretic analytic foundations in the reaction path of TiB2-TiC multiphase ceramics fabricated with Ti and B4C.