Three-dimensional network of multi-fold twins enabled by geometrically necessary amorphous zones

Three-dimensional multi-fold twin architectures are valuable for tailoring material properties but constructing them in man-made crystals remains challenging due to angular misfits from incomplete 360° space filling in large volumes, particularly lacking in-situ observations of crystal growth. Here, we successfully create three-dimensional architectures of plural multi-fold twins in a growing FeCoNiCuZn and the other multi-principal element alloy. The inherent chemical composition inhomogeneity entails twin fault energy variation across different {111} twinning planes, activating multiple twinning systems simultaneously. Importantly, we discover the commonly existed geometrically necessary amorphous zones in such three-dimensional multi-fold twin architectures. Combining in-situ transmission electron microscopy heating experiments and atomic electron tomography, we find that these geometrically necessary amorphous zones, typically several nanometers in size, fill the twin junctions and accommodate large geometric misfits, preventing crystallization even near the melting point.