Shear transformation zone analysis of anelastic relaxation of a metallic glass reveals distinct properties of α and β relaxations

Abstract

Shear transformation zone analysis of anelastic relaxation of a metallic glass reveals distinct properties of α and β relaxationsMetallic glasses with pronounced high-frequency β relaxation in their dynamic-mechanical response have been observed to exhibit large plasticity. Due to their disordered atomic structure, it is challenging to identify the microscopic mechanisms of their relaxation behavior. Quasistatic anelastic relaxation measurements have been performed over 10 orders of magnitude of time on La 55 Ni 20 Al 25 metallic glass, which exhibits a strong β relaxation. The corresponding time-constant spectra were computed from the data-they contain a series of peaks corresponding to an atomically quantized hierarchy of shear transformation zones (STZs), where both the α and β relaxations are consistent with the STZ model. Two different regimes of activation-volume increment between the peaks are observed, suggesting the involvement of different elements in STZs corresponding to α vs β relaxations. Room-temperature structural relaxation significantly affects the former but not the latter.

Thermodynamic–Dynamic Interrelations in Glass-Forming Polymer Fluids

“…Interestingly, anelastic measurements on metallic glass materials over a large frequency range have revealed direct evidence for a "quantized" activation energy spectrum for the secondary β-relaxation in these materials. 246,247 The energy landscapes found numerically for various simulated GF liquids indeed exhibit a remarkably general structure, resembling superficially the well-known energy level spacing characteristic of quantum harmonic oscillator. It seems also relevant to point out here that many-body dynamical systems have been observed to exhibit a classical analog of zero-point energy [248][249][250][251] associated with the emergence of an energy threshold, where the dynamic of the material first exhibits ergodic or "stochastic" dynamics rather than integrable or "regular" motion.…”

“…In particular, the estimated average energy of the saddles was found by a number of groups for a range of model GF liquids − to increase linearly with the order k of the saddle where energy is measured with respect to the energy minimum, inherent structure energy, to which the saddles are related. Interestingly, anelastic measurements on metallic glass materials over a large frequency range have revealed direct evidence for a “quantized” activation energy spectrum for the secondary β-relaxation in these materials. , …”

Analysis of the anelastic deformation of high-entropy Pd20Pt20Cu20Ni20P20 metallic glass under stress relaxation and recovery

“…Anelastic behavior during recovery process is an effective method to investigate the distribution and evolution of flow defects related to free-volume zones in HE-MGs [39,61]. The anelasticity originates from the microscopic heterogeneous behavior of MGs [63].…”

“…To further improve the characterization of the recovery behavior, a direct spectrum analysis was considered [65]. A single stretched exponent exp (−(𝑡𝑡/𝜏𝜏) 𝛽𝛽 ) has been used to describe the shape of the recovery spectrum [61]. However, as the recovery deformation in HE-MG involves several processes, the temporal evolution of the anelastic strain can be also modeled with the combination of exponentially decaying terms, exp (−𝑡𝑡/𝜏𝜏 𝑖𝑖 ) , with different time constants, 𝜏𝜏 𝑖𝑖 , as shown in the linear constitutive model depicted in Fig.…”

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“…On heating, these materials undergo nanocrystallization formation of primary aluminium [12][13][14][15][16] that leads to their additional hardening. The process of structural relaxation precedes crystallization [17].…”