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

97.4% of theoretical density was obtained for boron carbide (B 4C) 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 B 4C 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 B 4C to form SiC, Al 4C 3 and Al 4SiC 4 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.