Effect of microstructure on mechanical, electrical and thermal properties of B4C-HfB2 composites prepared by arc melting

B 4 C-HfB 2 composites were prepared by arc-melting using B 4 C and HfB 2 as raw materials. The eutectic composition of B 4 C-HfB 2 system was 70B 4 C-30HfB 2 (mol%) with a lamellar eutectic microstructure. HfB 2 about 1   μm in thickness was dispersed in B 4 C matrix uniformly of the eutectic composite, much smaller than raw powders. At the eutectic composition, the B 4 C-HfB 2 composites showed the maximum Vickers hardness (31.2   GPa) and fracture toughness (5.3   MPa   m 1/2 ) at room temperature, and maximum thermal expansion coefficient (7.1   ×   10 −6   K −1 ) from 293 to 1273   K. The electrical and thermal conductivity of B 4 C-HfB 2 composites increased with increasing HfB 2 content. The electrical conductivity of B 4 C-HfB 2 eutectic composites decreased from 8.94   ×   10 4 to 7.43   ×   10 4   Sm −1 with increasing temperature from 298 to 800   K, showing a metallic electrical behavior. The thermal conductivity of B 4 C-HfB 2 eutectic composite was 16–18 WK −1   m −1 from 298 to 973   K.