Characterization of flow units in metallic glass through structural relaxations

Abstract

We characterize the evolution of flow units associated with the flow “defects” in metallic glass by monitoring the fictive temperature change of a typical metallic glass upon isothermal annealing below its glass transition temperature. The correlations between the fictive temperature Tf, enthalpy change, and the concentration of flow units have been obtained. Such correlations help in understanding the evolution process of flow units, structural feature, and structural relaxation behaviors in metallic glasses, and can rationalize effects of the cooling rate, aging, and annealing on properties and structure of metallic glasses.

Structural perspectives on the elastic and mechanical properties of metallic glasses

“…(3). 35,36 This also means the concentration of flow units of a MG can be determined by monitoring the change of certain properties of the MG upon isothermal annealing, and the flow units concept helps in understanding the widespread mechanical behavior of metallic glasses.…”

The fracture of bulk metallic glasses

“…Compared with the elastic matrix, the defects of flow units are a group of atoms exhibiting a lower packing density, higher atomic mobility, higher energy dissipation rate, lower modulus, and higher energy states in the energy landscape [77][78][79][80][81][82][83][84][85]88]. The flow units show a collective rearrangement process during stress or thermal induced deformation.…”

“…(which act as the viscous flow units for deformation and glass transition) embodied in the elastic solid matrix, that is: metallic glass = ideal elastic glassy matrix + flow units [65,66,68,[79][80][81][82][83][84][85][86][87]. Compared with the elastic matrix, the defects of flow units are a group of atoms exhibiting a lower packing density, higher atomic mobility, higher energy dissipation rate, lower modulus, and higher energy states in the energy landscape [77][78][79][80][81][82][83][84][85]88].…”

Densification contribution as a function of strain rate under indentation of terbium-doped aluminophosphate glass

“…It was suggested [1] that different mechanisms may be responsible for the plastic deformation of glassy matrix, the main of which are the particular modes of shear flow [2][3][4][5][6][7] and permanent densification caused by the compression of material [8,9]. The contribution of each of these mechanisms to the total plastic deformation strongly depends on the composition and the resulting glass structure, particularly, on the atomic packing density [8,10].…”