Break-down of the relationship between {\alpha}-relaxation and equilibration in hydrostatically compressed metallic glasses

TL;DR

This study reveals that hydrostatic compression alters metallic glasses in ways that challenge the traditional view that alpha-relaxation solely governs their memory erasure, showing irreversible changes and additional relaxation processes.

Contribution

It demonstrates that pressure-induced modifications in metallic glasses lead to irreversible structural and dynamic changes, revealing new relaxation processes beyond alpha-relaxation.

Findings

Annealing under pressure irreversibly modifies glass properties.

Compressed glasses do not revert to the original supercooled liquid upon heating.

Pressure can be used to engineer glass properties under extreme conditions.

Abstract

Glasses encode the memory of any thermo-mechanical treatment applied to them. This ability is associated to the existence of a myriad of metastable amorphous states which can be probed through different experimental pathways. It is usually assumed that this memory can be erased in the supercooled liquid, and that this process occurs on a time scale controlled by the {\alpha}-relaxation. We find that this assumption does not apply for hydrostatically compressed glasses. Annealing under pressure a prototypical metallic glass can irreversibly modify its dynamics, thermodynamics and structure, reduce the atomic mobility and lead to structural modifications of the first coordination shells which reduce the thermal stability with respect to a glass annealed in absence of pressure. When heated above their glass transition temperature, these compressed glasses do not convert into the pristine supercooled liquid, implying the existence of an additional process, beyond the {\alpha}-relaxation, contributing to the equilibrium recovery of the material. These results establish pressure as a powerful tool for engineering non-equilibrium glassy materials with tailored properties, while deepening our understanding of relaxation dynamics in disordered systems under extreme conditions.