Synthesis of Dual Phase High Entropy Ultra‐High Temperature Ceramics From Different Carbon Sources

Dual phase (Hf,Nb,Ta,Ti,Zr)C‐(Hf,Nb,Ta,Ti,Zr)B 2 ceramics were synthesized by boro‐carbothermal reduction of oxides with different carbon black powders. The starting materials reacted differently based on the particle size, surface area, and additives in the carbon powder. Smaller powder‐particle sizes and the presence of oxygen‐containing functional groups increased the dispersibility of the carbon powder and led to more uniform reactions. Although increased surface area and structural disorder enhanced reactivity of the carbon, these characteristics also led to non‐uniform dispersion that caused problems with reaction. Increased net carbon content further increased the carbide phase proportion in the final sintered ceramics. This study demonstrates that powder reactions, residual oxides, and final proportions of targeted phases depend on the carbon powder. Carbon black powder with finer particle size that also contained additives promoted uniform dispersion and reaction while maintaining submicron‐sized grains after sintering, which increased hardness even though residual oxides were retained in the microstructure.