PROCESSING, MICROSTRUCTURE, AND MECHANICAL PROPERTIES OF B_4C - TiB_2 PARTICULATE SINTERED COMPOSITES

摘要

Pressureless sintering of boron carbide ceramics containing 0-25 vol. percent TiB_2 phase, produced via all in-situ chemical reaction between B_4C, TiO_2, and elemental carbon, was studied in the isothermal and constant-heating-rate regimes. The presence of TiB_2 results in a decrease in activation energy for sintering from 717 kJ/mol at 0 vol. percent TiB_2 to 266 kJ/mol at 25 vol. percent TiB_2. Ceramic bodies of B_4C - TiB_2 particulate composites with relative densities of up to 99 percent were sintered without pressure at temperatures of 2050-2100 deg C. Grain boundary diffusion is the primary mechanism of TiB_2 particle coarsening. TiB_2 particle size is bimodal depending on whether the particle is confined within a B_4C grain or located on the grain boundary. Densification behavior of the B_4C - TiB_2 system is identical at different heating rates in the temperature range of 1800-2150 deg C.