Relaxation decoupling in metallic glassy state

TL;DR

This paper reports a novel two-step relaxation process in metallic glasses below Tg, revealing a decoupling of dynamic modes with distinct mechanisms, challenging existing understanding of glass relaxation.

Contribution

It introduces the first observation of two-step relaxation dynamics in metallic glasses, highlighting a complex decoupling of atomic motion mechanisms.

Findings

Discovery of gradual transition from single to two-step relaxation

Identification of ballistic-like and subdiffusive relaxation modes

Implication of richer relaxation scenarios in metallic glasses

Abstract

Upon cooling, glass-forming liquids experience a two-step relaxation associated to the cage rattling and the escape from the cage, and the following decoupling between the \b{eta}- and the {\alpha}-relaxations. The found decoupling behaviors have greatly changed the face of glassy physics and materials studies. Here we report a novel dynamic decoupling that the relaxation function changes gradually from a single-step to a two-step form as temperature declines through the stress relaxation of various metallic glasses in a broad time and temperature range below glass transition temperature (Tg). Such a two-step relaxation is unexpected in glassy state and reveals a decoupling of dynamic modes arising from two different mechanisms: a faster one exhibiting ballistic-like feature, and a slower one associated with a broader distribution of relaxation times typical of subdiffusive atomic motion. This first observation of two-step dynamics in metallic glassy state points to a far richer-than-expected scenario for glass relaxation.