Microstructure characterization of ZrB ₂-SiC composite fabricated by spark plasma sintering with TaSi ₂ additive

Dense ZrB ₂-SiC composite was synthesized by spark plasma sintering with 10vol.% TaSi ₂ additive. When sintered at 1600°C, core-shell structure was found existing in the sample. The core was ZrB ₂ and the shell was (Zr,Ta)B ₂ solid solution. This result was ascribed to the decomposition of TaSi ₂ and the solid solution of Ta atoms into ZrB ₂ grains. The solid solution process probably decreased the boride grain boundary active energy, contributing to the formation of coherent structure of grain boundaries. Additionally, the existence of dislocations in the boride grains indicated that the applied pressure also imposed an important effect on the densification of composite. When sintered at 1800°C, owing to the atom diffusion, Ta atoms homogeneously distributed in the boride grains, leading to the disappearance of core-shell structure. The boundaries between (Zr,Ta)B ₂ grains, as well as between boride grains and SiC particles, were still clear without amorphous phase existing.