Intermediate structural state for maximizing the rejuvenation effect in metallic glass via thermo-cycling treatment

Abstract

Annealing of metallic glasses (MGs) at temperature near glass transition temperature (Tg) triggers relaxation and often hampers their performances in service. Rejuvenation treatment of MGs by thermal cycling is recently intensively investigated. However, the mechanism responsible for the structural rejuvenation still remains elusive. In this work, we present a systematic study on the rejuvenation effect of a Zr46Cu38Al8Ag8 MG annealed at 0.9Tg for various durations, subjected to thermo-cycling treatment. It is found that well relaxed samples after long-term annealing are almost unaffected, while short-term annealed samples exhibit large rejuvenation effect by thermo-cycling treatment. Using synchrotron X-ray diffraction, we find that thermal cycling results in a disordering at the short-range scale, where the rejuvenation effect is large in a heterogeneous sample. More interestingly, the thermo-cycling treatment on intermediate structure with 20 h-annealed sample relatively exhibits a high degree rejuvenation effect, as compared to shorter- and longer-term annealed samples. This finding indicates that the activation barrier for rejuvenation strongly depends on the original structural states, e.g., free volume, inherent stress and structural heterogeneity.