Stress breaks universal aging behavior in a metallic glass

Amlan Das,Eric M Dufresne,Chaoyang Liu,Robert Maaß,Peter M Derlet

doi:10.1038/s41467-019-12892-1

Abstract

Numerous disordered materials display a monotonous slowing down in their internal dynamics with age. In the case of metallic glasses, this general behavior across different temperatures and alloys has been used to establish an empirical universal superposition principle of time, waiting time, and temperature. Here we demonstrate that the application of a mechanical stress within the elastic regime breaks this universality. Using in-situ x-ray photon correlation spectroscopy (XPCS) experiments, we show that strong fluctuations between slow and fast structural dynamics exist, and that these generally exhibit larger relaxation times than in the unstressed case. On average, relaxation times increase with stress magnitude, and even preloading times of several days do not exhaust the structural dynamics under load. A model Lennard-Jones glass under shear deformation replicates many of the features revealed with XPCS, indicating that local and heterogeneous microplastic events can cause the strongly non-monotonous spectrum of relaxation times.

Highlights

Numerous disordered materials display a monotonous slowing down in their internal dynamics with age
Recent progress in coherent scattering methods has addressed this shortcoming via X-ray photon correlation spectroscopy (XPCS) or electron correlation spectroscopy that allow the direct measurement of the structural dynamics at the interatomic or interparticle length scale in disordered systems[5,6]
Before turning our attention to the detailed stressdependent dynamic behavior of the investigated metallic glasses (MGs), we briefly introduce some important aspects of the conducted experiments

Summary

Introduction

Numerous disordered materials display a monotonous slowing down in their internal dynamics with age. 1234567890():,; Significant structural evolution is a ubiquitous property of glassy materials, including polymeric glasses, oxide glasses, molecular glasses, and metallic glasses (MGs) The origin of this time-dependent evolution, typically referred to as aging, is the inherently out-of-equilibrium state, where local and thermally activated excitations reconfigure the atomic or molecular structure to lower the overall energy of the material[1]. For the MGs considered here, this means that the thermally activated atomicscale relaxation dynamics is insensitive to the structural state, as macroscopically captured with density or microscopically described with the degree of medium and short-range ordering Further support for such universal aging behavior has been provided by computer simulations that showed how τ increases linearly or sublinearly with tw23—a property known for numerous polymeric glasses[24] and spin glasses[25], thereby underlining the wide applicability of the time-waiting time superposition across structural and nonstructural glassy systems. As a function of time, relaxation times vary strongly with

Methods

Results

Conclusion