Transition from relaxation to rejuvenation in ultrastable metallic glass driven by annealing

Abstract Ultrastable metallic glasses (SMGs) are of exceptional interest as they are promising candidates to solve the stability issues of conventional metallic glasses. The annealing-driven structural evolution of a Zr50Cu44.5Al5.5 SMG fabricated by direct current magnetron sputtering, alongside its thermophysical and mechanical properties, were systematically investigated over the temperature range 0.74 to 1.03 T g , where T g is the glass transition temperature. A temperature limit for further improvements in key properties due to annealing was found at 0.8 T g , as a relaxation-to-rejuvenation transition was observed beyond this temperature. This transition temperature agrees well with the optimal temperature range for an SMG formation. The origin of this transformation resides in the local structure deviation from short range order- to medium range order- and the resultant disorder-dominated state upon annealing. Rejuvenation occurs upon the activation of α relaxation, as structural units revert to bulk-like behavior due to a liquid–liquid transition. The abnormal three-stage sub- T g relaxation pattern observed in SMG was caused by a non-monotonic change in structural heterogeneity as annealing temperature increased from 0.74 to 0.93 T g . This work firstly provides direct evidence for an annealing-induced structural evolution in SMG fabricated at room temperature and imparts a better understanding of the optimal temperature range for SMG formation.