High-entropy carbide ceramics with refined microstructure and enhanced thermal conductivity by the addition of graphite

Aiming at the refined microstructure and enhanced thermal conductivity of high-entropy carbide (HEC) ceramics for high-temperature applications, the addition effect of graphite was comprehensively investigated in this study. HEC ceramics incorporated with different contents of graphite were solidified by spark plasma sintering (SPS) using self-synthesized high-entropy (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C powder and graphite as starting materials. The results demonstrate that the incorporated graphite removed the oxygen impurity in the mixed powders, decreased the oxygen content and increased the lattice parameter of the HEC phase, and improved the densification behavior of HEC ceramics. On the other hand, the addition of graphite brings a refinement of HEC grains and improves the mechanical properties. More importantly, the thermal conductivity of the HEC ceramics was significantly increased owing to the removing effect of oxide impurity by the added graphite. It is considered that the lattice "purified" HEC grains with low oxygen content contribute to the improvement in thermal conductivity of the ceramics.