Microalloying suppresses the formation of ultrastable Ce-based bulk metallic glasses

Microalloying has been widely used to enhance the glass-forming ability and stability of metallic glasses. However, this study reveals that microalloying can effectively suppress the formation of ultrastable states in Ce-based bulk metallic glasses. Over a decade of natural aging at room temperature, thermal relaxation was accompanied by the shrinkage of Ce-rich vacancy-sized open spaces driven by transient Ce diffusion. The addition of transition metals (Ni, Fe, and Co) strongly hindered this process because of their strong bonding with Ce atoms. Notably, Fe and Co atoms strongly suppressed the shrinkage of vacancy-sized open spaces by impeding Ce diffusion, preventing the glass from descending into an ultrastable state despite thermal relaxation observable. These findings highlight the role of microalloying in influencing the stability and structural evolution of metallic glasses during long-term aging.