| Abstract Scope |
Local chemical and structural ordering can impact properties of complex alloys. In multi-principal element alloys, chemical short-range order can tune stacking fault energies and may enhance radiation tolerance. In metallic glasses, structural short-range order, such as geometrically unfavored motifs (GUMs), may significantly influences shear band formation. Understanding how local ordering evolves under mechanical deformation at the nanoscale is essential for designing advanced alloys. Here, we demonstrate the integration of in-situ nanomechanical testing with four-dimensional scanning transmission electron microscopy (4D-STEM), effectively creating a five-dimensional approach (5D-STEM) to probe these phenomena. Two examples will be presented. For CrCoNi medium-entropy alloys, we reveal that short-range order governs the reversibility of stacking faults and thereby controls deformation mechanisms. In bulk metallic glass, 4D-STEM mapping of packing density evolution, coupled with molecular dynamics simulation, provides experimental evidence linking structural motifs to shear band nucleation. |