Effect of physical aging on Johari-Goldstein relaxation in La-based bulk metallic glass

The influence of physical aging on the β relaxation in La₆₀Ni₁₅Al₂₅ bulk metallic glass has been investigated by mechanical spectroscopy. The amplitude of the β relaxation (ΔG″) decreases while its relaxation time (τ_β) increases during aging. We find that, as in organic glasses, the changes of ln (τ_β) and ln (ΔG_max) are linearly correlated with ln (τ_β) = b - a ln (G max ″). This behavior is discussed in term of the asymmetric double-well potential (ADWP) model, with U and Δ the energies characterizing the ADWP. It is suggested that during aging the ratio U/Δ remains approximately constant, with a value close to the coefficient describing the linear correlation between ln (τ_β) and ln (G max ″)(U/Δ ∼ a). Moreover, the evolution versus aging time of ΔG_max can be described by a simple stretched exponential equation giving values of τ_aging consistent with tan(δ) measurements during aging. The very similar behavior of the β relaxation during aging in metallic glasses and organic material strongly suggests a common nature for this relaxation.