Effect of boron carbide composition on its densification behavior during spark plasma sintering (SPS)

The effect of boron carbide composition on its sintering behavior was investigated. Boron carbide of various compositions was synthesized by reacting stoichiometric boron carbide with TiO₂. Titanium oxide was reduced by carbon that originated in stoichiometric boron carbide, leads to a decrease its carbon content and the formation of TiB₂ phase. Powder mixtures containing boron carbide of various boron to carbon ratios (x in B_xC was changed from 4.05 to 6.33) and different vol% of TiB₂ (from 6 to 21 vol%) were synthesized and densified by spark plasma sintering at 1800 and 1900 °C under an uniaxial pressure 50 MPa for 30 min. A mixture of stoichiometric boron carbide with 20 vol% TiB₂ was densified under the same conditions. The positive effect of boron carbide composition on the sintering behavior was clearly observed, while only minor effects of TiB₂ addition were detected. It was established that the carbon concentration in boron carbide gradually decreased in the 1200–1700 °C temperature range during spark plasma sintering and after sintering at 1800 and 1900 °C when the B to C ratio (x) was already close to its stoichiometric value, regardless of the initial carbon content. Mechanical properties of the sintered samples reflected their relative density. The maximum values of Young's modulus (450 ± 10 GPa), bending strength (840 ± 40 MPa) and hardness (35 ± 4 GPa) were obtained for fully dense specimens fabricated from the synthesized B_6.3C-21vol%TiB₂ mixture.