Effect of carbon contents on microstructure of B₄C/SiC composites

B₄C/SiC composites were obtained by reaction sintering between C/B₄C green body and liquid Si, and the effect of carbon contents on microstructure was investigated by OM and SEM. Results show that B₄C/SiC composites consist of three new phases, namely, SiC, B₁₃C₂, and B₁₂(C, Si, B)₃. Compared with composites without carbon addition, microstructure becomes more even and smaller with increased carbon contents ranging from 0 vol.% to 10 vol.%, which may be due to the generation of a small amount of SiC and the increase in grain boundary. However, when the carbon contents exceeded 10 vol.%, residual carbon can forms defects, and abnormal grain growth is clearly observed. Meanwhile, increased carbon addition, more SiC is generated results in poor distribution uniformity of each phase.