Key Structural Motifs Underlying the Unusual Deformation Flexibility and Phase-Change Propensity in Amorphous Alloys

This article presents a concise summary of our efforts over the past two decades, aimed at a foundational understanding of the structure-property relationship in amorphous alloys. The general materials science principle is that materials' behavior is determined by their microstructure, based on the concept of lattice + defects; this approach has been enormously successful in conventional alloys, which are all crystalline, but is no longer applicable to the metastable alloys with an entirely amorphous internal structure. Innovative ideas to overcome this dilemma have been emerging in recent years, and many milestones have been set. Starting from sub-nanometer-scale quasi-equivalent coordination polyhedra as the structural building blocks, key motifs that control each specific property are identified, out of the variety of motifs in the intrinsically heterogeneous short-to-medium range structure. Mechanical and crystallization/relaxation behaviors are used as examples to illustrate the correlations between the atomic-level structure, in particular the key motifs, and the properties of glassy materials. Guided by the structural insight, the extraordinary deformation and phase-change properties beyond crystalline alloys or unexpected for amorphous solids are demonstrated and explained. The core message is that by leveraging the key motifs, the internal structure of the amorphous alloys can be purposely tailored to target exceptional properties.