Nanoscale Origins of Mesoscale Organization: Creation, Evolution, and Self-Healing of Self-Assembled Dislocation Structures

Efficient self-assembly is widely observed in nature. However, development of beneficial self-organized microstructures are relatively rare in materials science, due in part to our incomplete understanding of self-organization mechanisms. Here, we investigate the multiscale evolution of two self-organized dislocation (SOD) patterns: dendritic petal-shaped dislocation loops and self-aligned loop walls in Fe-Cr alloys. While dislocation properties are predictable by conventional dislocation theory at the mesoscale, our study reveals that the complexity of SODs arises from atomistic interaction, driving complex hierarchy. Atomic-scale simulations and high-resolution transmission electron microscopy demonstrate that slight atomic-scale offsets in loop habit planes are critical for SOD pattern formation. Their special structure induces anisotropic strain fields, causing two-fold effects: directional growth due to surrounding strains and evolutionary decomposition due to internal strains. Contrary to classical self-organization models that assume isotropic elasticity, our findings reveal that defect formation and complex dislocations can be heavily influenced by anisotropy. The formation and evolution of complex hierarchical structures involve an elegant combination of fundamental rules in metallic crystals and establish a pathway for self-sustaining irradiation-resistant materials.