Microscopic Mechanisms of Plastic Deformation in High-Entropy Carbide (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C under Quasi-Isentropic and Ramp Compression

High-entropy carbides (HECs), which are characterized by pronounced chemical disorder and lattice distortion, exhibit exceptional strength-toughness synergy and are promising candidates for impact protection and high-temperature structural applications. However, their microstructural evolution and stress response under extreme conditions, such as high stress and strain rates, remains poorly understood. In this work, a high-accuracy machine-learning interatomic potential is employed to investigate the representative multi-principal carbide (Zr_0.2Hf_0.2Ti_0.2Nb_0.2Ta_0.2)C (HEC) through large-scale molecular dynamics (MD) simulations. To elucidate how multiple “high-entropy” effects govern atomic-scale plasticity in HECs, large-scale MD simulations are carried out to explore their response under quasi-isentropic compression and ramp-wave loading along three principal crystallographic orientations: [001], $[01\overline{1}]$, and [111]. The results demonstrate that the high-entropy effects profoundly reshape the initiation of plasticity, the competition among slip systems, and the localized deformation modes in HEC. Local stress fluctuations and lattice distortions enhance transient Bain-type stacking rearrangements within the sublattice and promote the synergistic activation of multiple slip systems. This leads to a transformation of shear band formation from isolated nucleation to a network-like propagation. Complementary first-principles calculations reveal that the carbon vacancy formation energy in high-entropy ceramics is significantly reduced compared to their single-component carbides. This reduction of vacancy formation energy facilitates preferential displacement of carbon atoms and their participation in shear band nucleation during compression. Furthermore, the comparison between different loading paths highlights the complexity of the high-entropy effects’ response. The quasi-isentropic loading path helps to unveil the intrinsic deformation mechanisms governed by the high-entropy effect itself, whereas the stress gradients inherent in ramp-wave loading couple with the high-entropy effect, leading to a premature triggering and intensification of plastic localization.