Enhanced Toughness of High‐Entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C Ceramics with the Incorporation of B4C

The high‐entropy carbide ceramic (HEC) (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C has attracted widespread attention due to its excellent mechanical properties and high‐temperature stability. However, its relatively low toughness has limited its widespread application. In this study, B 4 C/(Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C HEC with varying B 4 C molar ratios are prepared using high pressure and high temperature (HPHT) method ( P = 5 GPa, T = 2000 °C). The results indicate that the toughness of the highly dense (ρ > 8.0 g cm −3 ) composite high‐entropy carbide ceramics (HEC + B 4 C composite) initially increases and then decreases with increasing B 4 C content, reaching a maximum toughness value approximately twice that of pristine (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C, while the hardness remains unchanged ( K IC = 11.4 MPa m 1/2 , H V = 22.15 GPa). The different chemical bond strengths between B 4 C and (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C in the HEC + B 4 C composite lead to the formation of heterogeneous distribution of mechanical properties within the composite. This heterogeneity promotes significant crack deflection, crack branching, and bridging. This effectively disperses the stress at the crack tip, consumes fracture energy, and thereby improves the toughness of the samples. This research provides valuable insights into the strategy to reach a balance between hardness and toughness in advanced HEC ceramics.