| Abstract Scope |
Medium- and high-entropy alloys (M/HEAs) exhibit exceptional strength–ductility combinations, yet the atomic-scale mechanisms remain poorly understood. Using atomic electron tomography (AET), we directly map the 3D atomic structure of M/HEA nanoparticles, quantifying lattice distortion, strain heterogeneity, dislocation types, twin boundaries, and regions of chemical short-range order (CSRO). HEAs show greater lattice distortion and internal strain than MEAs, along with a higher density of Shockley partial and screw dislocations. Twinning is found to correlate with CSRO: twins nucleate in CSRO-deficient regions and are suppressed in CSRO-rich domains, providing direct evidence that local chemical order modulates stacking fault energy. During nanoparticle growth, most HEA nanocrystals merge coherently, while some form Σ3 twin boundaries, indicating that twinning can arise intrinsically during solidification. These results establish a direct link between atomic-scale chemical order, lattice distortion, and defect formation, offering new pathways for microstructural engineering of M/HEAs for enhanced mechanical performance. |