Annealing-Induced Plasticity and Strengthening in Metallic Glasses

Annealing-induced embrittlement has long been considered unavoidable in metallic glasses because it annihilates free volume (i.e., locally loosely-packed regions, LLPRs) required for plasticity. Here, we overturn this paradigm by demonstrating that sub-T_g annealing simultaneously increases both the strength and compressive plasticity of a chemically tailored Zr-based metallic glass, with plastic strain increasing by >150%. Our experimental analyses reveal that strategically employed Ni─Cu repulsion drives elemental partitioning during annealing, which seeds nanoscale chemical heterogeneity. Concurrently, atomistic simulations suggest the emergence of locally densely-packed regions (LDPRs) with characteristically low activation energy for shear transformation. These findings indicate that plasticity can be sustained by heterogeneous structures wherein densely-packed motifs, alongside conventional loosely-packed regions, serve as potential shear transformation sites. This shifts the design paradigm from merely introducing LLPRs to strategically engineering heterogeneous structures that enable compensatory plasticity.