Enhancing the Toughness of High-Entropy Carbide Ceramic (TiZrHfNbTa)0.2C through Composite B4C

Abstract The high-entropy carbide ceramic (HEC) (TiZrHfNbTa)0.2C has attracted widespread attention due to its excellent mechanical properties and high-temperature stability. However, lower than desired toughness limits its widespread application. In this paper, B4C/(TiZrHfNbTa)0.2C HEC with different molar ratios of B4C were prepared by high pressure and high temperature (HPHT) method (P = 5 GPa, T = 2000 ℃). The results indicate that the toughness of the composite high-entropy carbide ceramics (HEC + B4C composite) initially increases and then decreases with the increase of B4C content, with the maximum toughness being approximately 2 times that of (TiZrHfNbTa)0.2C while the hardness remains unchanged (KIC = 11.4 MPa·m1/2, HV = 22.15 GPa). The difference in the strength of chemical bonds between B4C and (TiZrHfNbTa)0.2C in the HEC + B4C composite leads to the formation of heterogeneous distribution of mechanical properties, introducing significant crack deflection, crack branching, and bridging. This effectively disperses the stress at the crack tip, consumes fracture energy, and improves the toughness of the samples. This study provides a significant contribution to the understanding how to balance the hardness and toughness of HEC.