Hierarchical Strain‐Modified Medium‐Entropy Carbide Ceramics Exhibit Exceptional Ablation Resistance up to 2400°C

Carbide ultrahigh-temperature ceramics (UHTCs) exhibit high melting points and are regarded as promising candidate materials for applications in ultrahigh-temperature conditions, such as high-speed flight vehicles. However, a high melting point alone is inadequate because thermal shock is typically associated with intense shear and oxidation, which require carbide UHTCs to not only have elevated temperature resistance but also robust structural stability. Herein, we present a reduced graphene oxide (rGO)-reinforced (HfZrTi)C medium-entropy ceramic (HZTMEC) that maintains structural integrity under thermal shock up to 2400°C and forms a dense and flat oxide layer. Notably, the addition of rGO induced a hierarchical strain modification spanning multiple length scales. At the microscale, rGO doping enhances atomic strain, refines grain size, and expands the distribution of high-strain regions, increasing dislocation density and hindering dislocation movement. At the mesoscale, the oxidation and volatilization of rGO during ablation create strip-shaped micropores in the oxide layer, dispersing the transformation stress and thermal stress generated by thermal shock. Therefore, long-term thermal stability without fracture over 2400°C was achieved in UHTCs. This study provides a valuable strategy for balancing ultrahigh-temperature ablation resistance and structural stability.