Microstructure of boron carbide pressureless sintered in an Ar atmosphere containing gaseous metal species

97.4% of theoretical density was obtained for boron carbide (B4C) ceramics by heating up to 2226 °C in an Ar atmosphere containing gaseous Al and Si species without external pressure. Impurities and secondary phases in the sintered B4C samples were examined by X-ray fluorescence and X-ray diffraction analyses respectively, which revealed that both Al and Si elements infiltrated into the green compacts and reacted with B4C to form SiC, Al4C3 and Al4SiC4 during the sintering. Triple junctions observed in the polished surfaces of the densified samples were filled by the secondary phases, indicating formation of liquid phase during heating. Dilatometric measurements at a constant heating rate in the Ar gas with the metallic gas species demonstrated that the shrinkage started at around 1700 °C, which was the liquid-phase formation temperature for the system reported in the previous studies. It was supposed that the liquid phase might be responsible for the densification.