Recently, the Institute of Mechanics of the Chinese Academy of Sciences, in cooperation with researchers at home and abroad, has made new progress in the aging resistance of glass materials. For the first time, the Institute of Mechanics of the Chinese Academy of Sciences has realized the extreme rejuvenation of the structure of a typical metallic glass in the ultra-fast time scale. The relevant results, entitled Ultrafast extreme rejuvenation of metallic glasses by shock compression, were published in Scientific Progress (Science Advances5: eaaw6249 (2019).
The metastable glass material has a spontaneous aging trend to the thermodynamic equilibrium state, accompanied by the deterioration of the properties of the material. However, through external energy input, the aging glass material can re-realize the younger (rejuvenation) of the structure. On the one hand, this anti-aging (anti-aging) process is helpful to the basic understanding of the complex dynamic behavior of glass, on the other hand, it is also beneficial to the engineering application of glass materials. In recent years, a series of structural rejuvenation methods based on non-affine deformation have been proposed for metallic glass materials with wide application prospects, in order to effectively regulate the mechanical and physical properties of the materials. However, all previous rejuvenation methods work at low stress levels and require a long enough time scale, so it has a great limitations.
Based on a double-target plate impact technique for light gas gun devices, the researchers achieved a rapid rejuvenation of typical zirconium-based metallic glass to a state of high enthalpy and extreme disorder in about 365nanoseconds (1/1000000 of the time it takes to blink once). The challenge of this technique is to apply several GPa magnitude monopulse loading and transient automatic unloading to metallic glass, so as to avoid dynamic failure of shear band, spallation and so on. At the same time, by controlling the impact speed of the flyer, the rapid rejuvenation of metallic glass can be "frozen" at different levels.
The researchers have comprehensively studied the ultra-fast rejuvenation process of metallic glass from the perspectives of thermodynamics, multi-scale structure and phonon dynamics "boson peak". It is revealed that the rejuvenation of glass structure is due to the formation of free volume induced by "shear transition" mode of nano-scale clusters. Based on this physical mechanism, a dimensionless Deborah number is defined to explain the time-scale possibility of ultra-fast rejuvenation of metallic glass. This work improves the time scale of rejuvenation of metallic glass structure by at least 10 orders of magnitude, expands the application field of this kind of materials, and deepens people's understanding of glass ultrafast dynamics.
Comparison of various structural rejuvenation methods of Metallic Glass: the relationship between excess relaxation enthalpy and rejuvenation time