Rejuvenation and Relaxation

A fundamental property of an amorphous solid is the ability to relax. As a function of time the system will find a lower energy state, which is also referred to as aging. To reverse aging remains a fundamental challenge. In metallic glasses, relaxation dynamics is typically explained with so called beta and alpha processes, each of which is characterized by a given relaxation time and energy scale. Using x-ray photon correlation spectroscopy, we find that residual stress fields around shear bands lead to unusual and an order of magnitude faster atomic dynamics. Such accelerated relaxation occurs over tens of micrometers away from the shear band. This means that metallic glasses that contain many shear bands will have a significantly different aging behavior than the as-cast material.

In addition to the ubiquitously known beta and alpha relaxations, we have recently also discovered a peak in the loss-modulus that occurs at much lower temperatures than the beta and alpha mode. We term this additional loss mechanism “γ-relaxation” in analogy to amorphous polymers, where this third relaxation mode has been known for a long time. It is found that γ-relaxation can be used to rejuvenate (reverse aging) the metallic glass significantly.

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