Deformation twinning plays a crucial role in the exceptional fracture toughness of low-stacking-fault energy (SFE) multi-principal-element alloys, yet the modulation mechanism of crack–twin boundary interactions at different twin orientations remains insufficiently understood. In this study, molecular dynamics simulations are employed to systematically investigate the influence of twin orientation on crack propagation behavior in the CoCrNi medium-entropy alloy. Comparative simulations are conducted on traditional face-centered cubic metals such as Cu and Ni under identical geometric configurations and loading conditions. By varying the inclination angle between the twin boundary and the crack propagation direction, three representative propagation modes are identified in CoCrNi: a penetration mode at low angles (0°–20°), a deflection mode at medium angles (30°–50°), and a blunting mode at high angles (60°–80°). Atomic-scale analyses reveal distinct crack-tip evolution mechanisms. At low angles, the crack penetrates the twin boundary through the emission of Shockley partial dislocations and the initiation of micro-twins, releasing the stress at the crack tip. At medium angles, the crack deflects along the twin boundary, accompanied by multistage plastic dissipation involving interfacial slip and twin thickening via twinning activity. At high angles, dense amorphous clusters and complex dislocation tangles form near the crack tip, where local stress is absorbed through internal damping, leading to crack blunting and arrest. These findings elucidate how twin orientation governs the interplay between twinning-induced plasticity and crack-tip evolution, establishing an atomistic framework for orientation-dependent crack–interface interactions. This work provides theoretical guidance for tailoring twin geometry and twinning activity to achieve enhanced strength–toughness synergy in low-SFE CoCrNi alloys.
Zhang et al. (2026) studied this question.