Structure-dynamics relationships in cryogenically deformed bulk metallic glass

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 Cu44Zr-44Al8Hf2Co2 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 (alpha-, beta- and gamma-transition) in glassy materials. The results suggest that the structural footprint of the beta-transition is related to entropic relaxation with characteristics of a first-order transition. Dynamic mechanical analysis data shows that in the range of the beta-transition, non-reversible structural rearrangements are preferentially activated. The low-temperature.-transition is mostly triggering reversible deformations and shows a change of slope in the entropic footprint suggesting second-order characteristics.

Automated summary

In-situ X-ray diffraction is used to study structural rearrangements during annealing processes in Cu44Zr-44Al8Hf2Co2 bulk metallic glass. The deformation-induced rejuvenation reveals a structural footprint that can be correlated to calorimetric signals, showing characteristics of a first-order transition for the beta-transition. Dynamic mechanical analysis data indicates that non-reversible structural rearrangements are preferentially activated during the beta-transition, while reversible deformations dominate the low-temperature alpha-transition with second-order characteristics.