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. Here we use in-situ X-ray diffraction to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature in Cu44Zr44Al8Hf2Co2 bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature. 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. With synchrotron radiation, temperature and time resolutions comparable to calorimetric experiments are possible. 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. The results suggest that the structural footprint of the β-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the β-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature γ-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.
We thank DESY (Hamburg, Germany), a member of the Helmholtz Association (HGF), for providing experimental facilities. Parts of this research were carried out at PETRA III using the Powder Diffraction and Total Scattering beamline P02.1. The research leading to our findings took place in the framework of project CALIPSOplus under the Grant Agreement 730872 of the EU Framework Programme for Research and Innovation HORIZON 2020 (F.S., B.S., and E.S.). This work was funded by the European Research Council under the ERC Advanced Grant INTELHYB (grant ERC-2013-ADG-340025, J.E., B.S., and A.R.), the ERC Proof of Concept Grant TriboMetGlass (grant ERC-2019-PoC-862485, J.E.), and by the Austrian Science Fund (FWF) under project grant I3937-N36 (B.S. and A.R.). We thank Dr. Christoph Gammer and Dr. Ivan Kaban for fruitful discussions. Cameron Quick, MChem. is thanked for English language editing.
© 2022, The Author(s).