Abstract:
The atomistic mechanisms governing aging and rejuvenation in metallic glasses are still unclear. In-situ X-ray diffraction allows to investigate the structural rearrangements during annealing from 77 K up to the crystallization temperature of CuZrAlHfCo bulk metallic glass rejuvenated by high pressure torsion performed at cryogenic temperatures and at room temperature.
The structural evolution was evaluated by dynamic mechanical analysis as well as by differential scanning calorimetry to determine relaxation dynamics and crystallization behavior. 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 new 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 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. The DMA 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.
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