Ceramic eutectic composites based on B4C directionally reinforced by high-entropy (TiZrHfNbTa)B2 boride

Directionally solidified B4C/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 eutectic high-entropy ceramics were prepared by the floating zone method based on the crucibleless zone melting of compacted powders using B4C and transition metal diboride (TiB2, ZrB2, HfB2, NbB2, TaB2) powders as initial materials. The structure of as-prepared composites consists of a B4C matrix uniformly reinforced by a single-phase high-entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 diboride. The XRD analysis of the composites confirmed the presence of the following phases in their compositions: B4C and (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2. The effect of the solidification rate on structural and mechanical characteristics of the B4C/(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 ceramics was revealed. It was found that an increase in the solidification rate leads to a decrease in the size of the reinforcing phase and an increase in hardness and fracture toughness from 36 to 39 GPa and 5.9-7.3 MPa center dot m1/2, respectively.