- The slow β relaxation is understood to be a universal feature of glassy dynamics. Its presence in bulk metallic
glasses (BMGs) is evidence of a broad relaxation time spectrum that extends to deep within the glassy state.
Despite the breadth of research devoted to this phenomenon, its microscopic origin is still not fully understood.
The low-temperature aging behavior and atomic structural rearrangements of a Au₄₉Cu₂₆.₉Si₁₆.₃Ag₅.₅Pd₂.₃ BMG
are investigated in the regime of the slow β relaxation by employing an ensemble of experimental techniques such
as high-intensity synchrotron x-ray scattering, modulated differential scanning calorimetry (MDSC), dynamic
mechanical analysis (DMA), impulse excitation, and dilatometry. Evidence of a distinct slow β-relaxation regime
is seen in the form of (1) an excess wing of the DMA loss modulus beginning at ∼50 °C, (2) a crossover effect
of elastic modulus with isothermal aging at 50 °C, and (3) a broad, nonreversing and largely irreversible sub-Tg
endotherm in theMDSC results. Atomic rearrangements occurring at the onset of the measured slow β-relaxation
temperature regime were found to be confined mainly to the short-range order length scale while no significant
atomic rearrangements occur on the length scale of the medium-range order. Furthermore, evidence is presented
that suggests the crossover effect in Young’s modulus is due to the evolution of chemical short-range order. These
results support the emergent picture of a dynamically heterogeneous glassy structure, in which low-temperature
relaxation occurs through atomic rearrangements confined mostly to the short-range order length scale.
- Evenson, Z., Naleway, S. E., Wei, S., Gross, O., Kruzic, J. J., Gallino, I., ... & Busch, R. (2014). β relaxation and low-temperature aging in a Au-based bulk metallic glass: From elastic properties to atomic-scale structure. Physical Review B, 89(17), 174204. doi:10.1103/PhysRevB.89.174204
|Funding Statement (additional comments about funding)
- Alexander von Humboldt Foundation Fredrick Wilhelm Bessel Research Award
- Project No. 16843N of the German Federation of Industrial Research Associations (AiF/IGF)
- Deutsche Forschungsgemeinschaft (German Research Foundation) through Grant No. GA 1721/2-1.J.J.K.
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