Abstract
Plastic deformation of metallic glasses performed at temperatures well below the glass transition proceeds via the formation of shear bands. In this contribution, we investigated shear bands originating from in situ tensile tests of Al88Y7Fe5 melt-spun ribbons performed under a transmission electron microscope. The observed contrasts of the shear bands were found to be related to a thickness reduction rather than to density changes. This result should alert the community of the possibility of thickness changes occurring during in situ shear band formation that may affect interpretation of shear band properties such as the local density. The observation of a spearhead-like shear front suggests a propagation front mechanism for shear band initiation here.
Highlights
Deformation processes in metallic glasses are different from those in crystalline materials due to the absence of a periodic lattice
Deformation tests on metallic glasses well below the glass transition temperature using deformation rates less than 10−2 have shown that the plastic flow is confined to narrow regions called shear bands when the applied strain exceeds the elastic range [1,2,3,4,5,6]
Whereas the interpretation of contrast changes in transmission electron microscopy (TEM) is often complicated [30,31,32], investigations on Al88 Y7 Fe5 metallic glass deformed ex situ by cold rolling have revealed local contrast changes within shear bands, which have been successfully determined as density changes using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in combination with foil thickness measurements [11,33,34]
Summary
Deformation processes in metallic glasses are different from those in crystalline materials due to the absence of a periodic lattice. Deformation tests on metallic glasses well below the glass transition temperature using deformation rates less than 10−2 have shown that the plastic flow is confined to narrow regions called shear bands when the applied strain exceeds the elastic range [1,2,3,4,5,6]. An important issue is the quantification of free volume [24] or density inside shear bands [11]. Whereas the interpretation of contrast changes in transmission electron microscopy (TEM) is often complicated [30,31,32], investigations on Al88 Y7 Fe5 metallic glass deformed ex situ by cold rolling have revealed local contrast changes within shear bands, which have been successfully determined as density changes using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in combination with foil thickness measurements [11,33,34].
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