- The dynamic response of boron carbide-silicon carbide (B 4 C-SiC) composites was studied in planar impact experiments, using a 25-mm gas gun accelerating 1.5-mm thick tungsten impactors to velocities in the 750-850 m/s range. The velocity of composite sample-PMMA window interface was continuously monitored by Velocity Interferometer System for Any Reflector (VISAR). The composites were prepared by pressureless infiltration of porous B 4 C ceramic preforms by molten silicon with and without carbon addition. During the infiltration process, molten silicon reacts with the B 4 C preform and with free carbon, resulting in the formation of SiC. The Hugoniot Elastic Limit values, σ HEL , of the ceramic samples were derived from the records of the velocity of the sample-window interface. The σ HEL values were in the 11-15 GPa range and are affected by the presence of the residual silicon and by the morphology of the newly formed SiC. Analysis of the inelastic part of the VISAR records allowed concluding that the presence of residual silicon controls the failure of the B 4 C-SiC composite in compression.