In the present study, mixtures of presynthesized HEB (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)B₂  powders and 5 vol.%, 10 vol.%, 15 vol.%, 20 vol.% and 25 vol.% SiC were subjected to ball milling followed by Spark Plasma Sintering (SPS) at 1900 °C to obtain highly dense (up to 99.5%) HEB-SiC composites. HEB of this particular composition was synthesized using boro/carbothermal reduction of oxide mixtures at 1800°C. XRD analysis of both the as-synthesized powder and the sintered HEB compacts showed a single hexagonal phase without any remaining, unreacted oxide impurities. Lattice parameters of the sintered HEB compacts determined by Rietveld analysis were in good match with the results theoretically predicted by Ab Initio calculations. The addition of SiC significantly improved densification of HEB materials. The room temperature mechanical properties, such as hardness, flexural strength and fracture toughness continuously increased with the increasing amount of SiC up to 20 vol.%. A significant drop in the mechanical properties observed for the composite with 25 vol.% was caused by the significant coarsening of the microstructure. On the other hand, the dynamic oxidation rate of the materials significantly, almost linearly decreased with the addition of SiC up to 25 vol.%. It was concluded that the (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)B2 composite sintered with 25 vol.% SiC showed the best combination of room and high temperature mechanical properties.

Acknowledgement 
This work was supported by the Slovak Research and Development Agency under the contract no. APVV-21-0402 and APVV-SK-CZ-RD-21-0089. The support of project VEGA 2/0110/21 is also acknowledged. This study was performed as part of the implementation of the project “Building-up Centre for advanced materials application of the Slovak Academy of Sciences”, ITMS project code 313021T081, supported by the Research & Innovation Operational Programme funded by the ERDFT.