Two Negatives Make a Positive: Understanding Strength Insensitivity to Point Defects in (HfNbTaTiZr)C High-Entropy Carbide Ceramic

Ideal strength represents the theoretical maximum load-bearing capacity of a defect-free crystal. However, real-world materials inevitably contain defects that degrade their mechanical performance. High-entropy carbide ceramics (HECCs) have received widespread attention due to their excellent mechanical properties, but the mechanisms underlying their defect tolerance remain unclear. In this study, ideal shear strength, deformation modes, and defect-induced mechanical responses of (HfNbTaTiZr)C and its constituent carbides were investigated using first-principles calculations. The results showed that although the ideal shear strength of (HfNbTaTiZr)C follows the weakest link rule due to inherent lattice distortion, this rule fails as point defects appear. Generalized stacking fault energy and Bader charge analyses indicate that the multielement composition of HECCs would mitigate the impact of point defects on mechanical performance. Comparing the shear strength and deformation modes of (HfNbTaTiZr)C and its constituent multicomponent carbides with/without point defects reveals that lattice distortion could significantly reduce the strength sensitivity of HECCs to defects, underpinning their superior mechanical stability.