A comprehensive atomistic analysis of the experimental dynamic-mechanical response of a metallic glass

Abstract

It is shown that assumed anelastic relaxation-time spectra can be recovered reliably from simulated loss–modulus curves that include noise by nonlinear least-squares fitting. The same method is used to obtain spectra for published experimental data on a metallic glass. The results provide a comprehensive kinetic picture of the atomically quantized hierarchy of shear transformation zones (STZs). We resolve a window of STZs consisting of 25–33 atoms, and a simultaneous fit yields the Arrhenius behavior for each size. The corresponding activation energies are 1.75–2.31 eV. The high activation energy that is often observed above Tg is shown to be an artifact of the temperature dependence of the high-frequency shear modulus. The hierarchy of STZ sizes is consistent with both a and b relaxations, suggesting that they originate from the same microscopic mechanism.