Metastable glasses will age spontaneously towards their equilibrium state, which is usually associated with the degradation of their properties. However, aged glasses can structurally rejuvenate with external energy injection. This anti-aging process provides insights into their complicated dynamics, and extends their practical applications.
In existing rejuvenation strategies, sufficiently long timescales are needed because the strategies have to work under relatively low stresses. Therefore, rejuvenating a glass at very short timescales is intriguing.
Recently, a group of scientists led by Institute of Mechanics of the Chinese Academy of Sciences has achieved the ultrafast rejuvenation of metallic glasses by shock compression. The study was published in Science Advances.
The scientists used a light-gas gun facility to conduct plate impact experiments. With a specially designed self-unloading double-target technique, they presented the first experimental evidence that metallic glasses can be rapidly rejuvenated to extremely-high-enthalpy states within the ever-known shortest timescale of about 365 ns, while without the introduction of shear bands or other damages.
By controlling the shock stress amplitude, the shock-induced rejuvenation can be successfully frozen at different degrees.
The rejuvenated glasses are extensively characterized in terms of their thermodynamics, multi-scale structures, and vibrational dynamics through boson heat capacity peaks.
Besides, the scientists revealed that the atomic free volume creation mediated by nanoscale shear transformations acts as the physical mechanism for the observed rejuvenation of metallic glasses.
A Deborah number, defined as a competition of timescales between the net structural disordering and the applied loading, is introduced to explain why the ultrafast rejuvenation takes place within a very short time window.