Stress breaks universal aging behavior in a metallic glass

Area of Science:

• Materials Science
• Condensed Matter Physics
• Rheology

Background:

• Disordered materials, particularly metallic glasses, exhibit age-dependent dynamics characterized by a universal superposition principle.
• This principle relates time, waiting time, and temperature for internal dynamics across various conditions.

Purpose of the Study:

• To investigate the effect of mechanical stress on the universal dynamics of metallic glasses.
• To determine if mechanical stress maintains or breaks the established time-temperature superposition principle.

Main Methods:

• In-situ X-ray Photon Correlation Spectroscopy (XPCS) experiments were performed on metallic glasses under mechanical stress.
• A model Lennard-Jones glass under shear deformation was used for computational validation.

Main Results:

• Mechanical stress within the elastic regime breaks the universality of dynamics in metallic glasses.
• Strong fluctuations between slow and fast structural dynamics were observed, with generally larger relaxation times under stress.
• Relaxation times increased with stress magnitude, and structural dynamics remained active even after prolonged preloading.

Conclusions:

• Mechanical stress introduces significant heterogeneity and non-monotonicity into the relaxation time spectrum of metallic glasses.
• Local, heterogeneous microplastic events are likely responsible for the observed complex dynamics under shear deformation.