Abstract: Multifunctional carbon fibers (Cf )/ZrB2 based composites were synthesized through a series of processes termed as IVI including sequential slurry injection, vacuum impregnation, pyrolysis and reimpregnation cycles, which facilitated the effective incorporation of ZrB2 powder into the carbon fiber preform. A single IVI cycle reduced the porosity of the preform from ∼77 % to ∼40 %. Microstructural analysis revealed a preferential distribution of ZrB2 powders within random layers and pyrolytic carbon effectively bridging the ceramic particles and fibers. Due to the hierarchical 0 °/90 °carbon fiber architecture, as fabricated Cf /ZrB2 composites exhibited anisotropy in mechanical and physical properties. Vertically oriented com-posites demonstrated higher compressive strain and low thermal conductivity (1.00-2.59 W m-1 K-1 from 298 to 1173 K). In contrast, horizontally oriented specimens exhibited higher compressive strength (60.77 ±20.30 MPa) and thermal conductivity (1.6-4.5 W m-1 K-1 from 298 to 1173 K). Furthermore, the continuous Cf endowed the composites with a positive temperature-dependent electrical conductiv-ity characteristic, not only contributed to their higher electrical conductivity values, but also was helpful for maintaining the excellent EMI shielding effectiveness (19.80-22.51 dB) of Cf /ZrB2 up to 800 °C without obvious degradation. Considering the low-density characteristics of as-prepared composites, their specific performance metrics demonstrate good competitiveness compared to those fabricated via alternative pro-cesses.

Key words: UHTCs, Boride, Anisotropic thermal conductivity, Electromagnetic shielding efficiency, Extreme-environment materials