Internal friction and dynamic shear modulus of a metallic glass in a seven-orders-of-magnitude frequency range

We report measurements of the internal friction and shear modulus of glassy Cu49Hf42Al9 at sub-hertz frequencies (0.03-1 Hz) and at a high frequency of 560 kHz at temperatures from the room one up to well above the glass transition temperature T-g. It is found that an increase of the frequency in this range results in a drastic decrease of the internal friction and shear modulus relaxation both below and above T-g. The relaxation kinetics is analyzed within the framework of a classical phenomenological approach in terms of the real and imaginary parts of the dynamic shear compliance both for the initial and relaxed states of the glass under investigation. A law describing the frequency dependence of the imaginary compliance component in the whole frequency range investigated is determined. A new method for the determination of the Gibbs activation energy of relaxation is derived. The underlying activation energy spectrum determined on this basis is found to smoothly increase with the activation energies accessible in the experiment. A change of the activation energy with temperature below and above T-g is determined. The phenomenological analysis is combined with a physical interpretation of the relaxation, which is assumed taking place due to the activation of interstitial-type defects (essentially elastic dipoles) frozen-in from the melt upon glass production. It is argued that there exist at least three mechanisms of energy losses, which are related to changes of the dipoles' orientation in the same energy states and transitions between their low- and high-energy states. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study reports measurements of internal friction and shear modulus of glassy Cu49Hf42Al9 at different frequencies and temperatures. It is found that the relaxation of internal friction and shear modulus decreases with increasing frequency in the investigated range. A new method for determining the Gibbs activation energy of relaxation is derived, and the underlying activation energy spectrum is found to smoothly increase with accessible activation energies in the experiment.