Unveiling the structural arrangements responsible for the atomic dynamics in metallic glasses during physical aging

TL;DR

This study uncovers the complex atomic mechanisms behind physical aging in metallic glasses, revealing how structural rearrangements and medium-range ordering influence atomic dynamics and aging regimes.

Contribution

It provides the first direct connection between microscopic structural mechanisms and atomic motion in metallic glasses during aging, using combined dynamical and structural synchrotron techniques.

Findings

Atomic motion is dominated by stress-releasing rearrangements and medium-range ordering.

A secondary relaxation process emerges at higher temperatures, indicating precursors to crystallization.

Medium-range ordering occurs without affecting local density, involving localized relaxations.

Abstract

Understanding and controlling physical aging, i.e. the spontaneous temporal evolution of out-of-equilibrium systems, represents one of the greatest tasks in material science. Recent studies have revealed the existence of a complex atomic motion in metallic glasses, with different aging regimes in contrast with the typical continuous aging observed in macroscopic quantities. By combining dynamical and structural synchrotron techniques, for the first time we directly connect previously identified microscopic structural mechanisms with the peculiar atomic motion, providing a broader unique view of their complexity. We show that the atomic scale is dominated by the interplay between two processes: rearrangements releasing residual stresses related to a cascade mechanism of relaxation, and medium range ordering processes, which do not affect the local density, likely due to localized relaxations of liquid-like regions. As temperature increases, a surprising additional secondary relaxation process sets in, together with a faster medium range ordering, likely precursors of crystallization.