- The dynamic response of two boron carbide-based composites was studied in planar impact experiments (impact velocities 100–1000 m/sec) using a 25 mm gas gun. The composites were fabricated by infiltration of compacted B 4 C B and partially sintered B 4 C B preforms by molten Si. In the course of the infiltration process, the liquid silicon reacts with the B 4 C B phase resulting in the formation of the SiC and B 12 (B,C,Si ) 3 B phases along with some residual silicon present in the infiltrated composites. The velocities of the sample-PMMA window interface were monitored continuously by VISAR. The composites display a relatively high HEL (12–14 GPa) and spall strength (about 1 GPa) values. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were used to characterize the fracture surface. The correlation between the microstructure of the infiltrated composites and their dynamic response is discussed.