β relaxation is a key dynamic feature of glasses, influencing a wide range of properties. Although many factors, such as thermal history and composition, have been extensively studied and reported to significantly influence β relaxation, considerable controversy persists, limiting a deeper understanding of β relaxation in glasses. Here, we employ a binary metallic glass (MG), ${\mathrm{Ce}}_{75}{\mathrm{Al}}_{25}$, as a model system with a polymorphic crystallization process to minimize thermally induced compositional deviations. This enables us to separate and analyze the thermal and compositional impacts on β relaxation using dynamic mechanical analysis (DMA) across various thermal annealing treatments below the glass transition temperature $\left(T_g\right)$ and above the crystallization temperature $\left(T_x\right)$. We clarify that relaxation dynamics at temperatures not far below $T_g$ are primarily governed by α relaxation, and changes to the energy states of glasses (or atomic structures) through sub-$T_g$ annealing have minimal impact on β relaxation signals. These findings suggest that the β relaxation of ${\mathrm{Ce}}_{75}{\mathrm{Al}}_{25}$ MG is in fact a pseudo Johari-Goldstein (JG) relaxation rather than a genuine JG β relaxation. It is suggested that β relaxation behaves more like a localized dynamic event involving only a fraction of atoms, which may aid in crystallization nucleation below $T_g$. By contrasting the effects of thermal annealing on other Ce-Al binary MGs with primary crystallization processes, we further reveal that the position of β relaxation is primarily composition-dependent. These results shed new light on the thermal and compositional effects on β relaxation in MGs.

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• Composition
• Thermal properties
• Glassy systems
• Metallic glasses
• Thermomechanical analysis