The effect of cryogenic thermal cycling on aging, rejuvenation, and mechanical properties of metallic glasses

TL;DR

This study uses molecular dynamics simulations to explore how cryogenic thermal cycling affects the aging, rejuvenation, and mechanical properties of metallic glasses, revealing optimal amplitudes for energy minimization and mechanical strength.

Contribution

It demonstrates how thermal cycling can rejuvenate or further relax metallic glasses depending on initial conditions and cycling parameters, providing insights into optimizing their properties.

Findings

Poorly annealed glasses lower potential energy with cycling.

Well annealed glasses can be rejuvenated at high amplitudes.

Maximum elastic modulus and stress overshoot occur at specific cycling amplitudes.

Abstract

The structural relaxation, potential energy states, and mechanical properties of a model glass subjected to thermal cycling are investigated using molecular dynamics simulations. We study a non-additive binary mixture which is annealed with different cooling rates from the liquid phase to a low temperature well below the glass transition. The thermal treatment is applied by repeatedly heating and cooling the system at constant pressure, thus temporarily inducing internal stresses upon thermal expansion. We find that poorly annealed glasses are relocated to progressively lower levels of potential energy over consecutive cycles, whereas well annealed glasses can be rejuvenated at sufficiently large amplitudes of thermal cycling. Moreover, the lowest levels of potential energy after one hundred cycles are detected at a certain temperature amplitude for all cooling rates. The structural transition to different energy states is accompanied by collective nonaffine displacements of atoms that are organized into clusters, whose typical size becomes larger with increasing cooling rate or temperature amplitude. We show that the elastic modulus and the peak value of the stress overshoot exhibit distinct maxima at the cycling amplitude, which corresponds to the minimum of the potential energy. The simulation results indicate that the yielding peak as a function of the cycling amplitude for quickly annealed glasses represents a lower bound for the maximum stress in glasses prepared with lower cooling rates.