Rejuvenation to relaxation transition and liquid memory effect in La-based metallic glasses with different energy states

Rejuvenation of metallic glasses (MGs) under cryogenic thermal cycling (CTC) has been intensively studied due to its great theoretical and practical value. However, the relationship between energy states of MGs and rejuvenation capacity is still unclear. Here, a systematic study is performed on how the initial state of MGs affects the rejuvenation effect, and the difference in the initial state of MGs is mainly depicted by the fictive temperature Tf, as well as mechanical properties. A "rejuvenation to relaxation" transition upon Tf increasing is found among samples, and the critical energy state (Tf,c similar to 1.1T(g)) at which the transition occurs are further determined. The transition towards relaxation above Tf,c is attributed to the first CTC intervention of the local structures that are smaller than structural units involved in slow beta-relaxations. Besides, the CTC-induced recovery of MGs with a low Tf towards high temperature supercooled liquids has been found, and this behavior relates to the memory effect of MGs upon cooling process. When the liquid memory of MGs is awakened by CTC, the recovery to higher energy state (rejuvenation) occurs. This work supplements rejuvenation mechanism of MGs with different initial states, and provides a possibility to predict the evolution direction (rejuvenation or relaxation) of MGs by their energy states (or T-f).