Mechanical relaxation in supercooled liquids of bulk metallic glasses

We report the mechanical relaxation behaviors in typical supercooled liquids of bulk metallic glasses (BMGs). The metallic supercooled liquids are ideal systems for studying intrinsic motions of glass-former supercooled liquids because their structure is close to the simple "dense random packing of spheres'' model. We show that the primary relaxation in the frequency domain is dissipative and can be described by the empirical Kohlrausch-Williams-Watts function, and the temperature dependence of the primary relaxation time has the Vogel-Fulcher-Tamman form. Beyond the primary relaxation, an excess wing is found on the high-frequency tail of the primary relaxation. A corresponding shoulder is exhibited at a given frequency in the temperature region below the glass-transition temperature. The experimental results confirm that the decoupling between the slow beta relaxation and the primary (a) relaxation exists in metallic supercooled liquids. Based on the current models of the glass transition, we demonstrate that the dynamically heterogeneity originates in the heterogeneous microstructure of metallic supercooled liquids, and a picture of the heterogeneous microstructure is provided. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim