![]() ![]() Recent developments in the understanding of the atomic-scale mechanisms of rejuvenation from computer simulations have developed very insightful knowledge regarding the structural and thermodynamic origin of aging and rejuvenation due to either thermal processing or mechanical (or cyclic) loadings 11, 12, 13. All these studies reveal promising enhancement of mechanical properties without fully resolving their atomistic origins. The degree of rejuvenation and, hence, the amount of the stored energy as well as the free volume in a BMG can be controlled by different methods such as deformation 4, 5, high-pressure torsion (HPT) 6, ion irradiation 7, flash annealing 8, or even cooling to cryogenic temperatures 9, 10. ![]() Many efforts have been undertaken to tune the aging and rejuvenation. As aging leads to enhanced brittleness, it was found to be detrimental for many potential applications of BMGs. The first studies on aging due to the mechanical degradation of glassy polymers emerging in the 1950s and the fact that aging and rejuvenation occur (as discussed by Kovacs 1), culminated in a lively discussion about the existence of rejuvenation by Struik and McKenna in the late 1990s and the early years of this millennium 2, 3. The atomistic mechanisms underlying the aging and rejuvenation of bulk metallic glasses (BMGs) still remain unclear to a great extent. The low-temperature γ-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics. Dynamic mechanical analysis data shows that in the range of the β-transition, non-reversible structural rearrangements are preferentially activated. The results suggest that the structural footprint of the β-transition is related to entropic relaxation with characteristics of a first-order transition. This opens hitherto unavailable experimental possibilities allowing to unambiguously correlate changes in atomic configuration and structure to calorimetrically observed signals and can attribute those to changes of the dynamic and vibrational relaxations ( α-, β- and γ-transition) in glassy materials. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. Using a measure of the configurational entropy calculated from the X-ray pair correlation function, the structural footprint of the deformation-induced rejuvenation in bulk metallic glass is revealed. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in C u 44 Z r 44 A l 8 H f 2 C o 2 bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. The atomistic mechanisms occurring during the processes of aging and rejuvenation in glassy materials involve very small structural rearrangements that are extremely difficult to capture experimentally. ![]()
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