Ultrastable metallic glass by room temperature aging

Glasses have markedly different stability around their glass transition temperature (T_g), and metallic glasses (MGs) are conventionally regarded as metastable compared to other glasses such as silicate glass or amber. Here, we show an aging experiment on a Ce-based MG around its T_g (~0.85T_g) for more than 17 years. We find that the MG with strong fragility could transform into kinetic and thermodynamic hyperstable state after the long-term room temperature aging and exhibits strong resistance against crystallization. The achieved hyperstable state is closer to the ideal glass state compared with that of other MGs and similar to that of the million-year-aged amber, which is attributed to its strong fragility and strong resistance against nucleation. It is also observed through the asymmetrical approaching experiment that the hyperaged Ce-based MG can reach equilibrium liquid state below T_g without crystallization, which supports the idea that nucleation only occurs after the completion of enthalpy relaxation.