Shear-induced chemical segregation in a Fe-based bulk metallic glass at room temperature

Abstract

Shear-induced segregation, by particle size, is known in the flow of colloids and granular media, but is unexpected at the atomic level in the deformation of solid materials, especially at room temperature. In nanoscale wear tests of an Fe-based bulk metallic glass at room temperature, without significant surface heating, we find that intense shear localization under a scanned indenter tip can induce strong segregation of a dilute large-atom solute (Y) to planar regions that then crystallize as a Y-rich solid solution. There is stiffening of the material, and the underlying chemical and structural effects are characterized by transmission electron microscopy. The key influence of the soft Fe–Y interatomic interaction is investigated by ab-initio calculation. The driving force for the induced segregation, and its mechanisms, are considered by comparison with effects in other sheared media.

Direct Observation of Quadrupolar Strain Fields forming a Shear Band in Metallic Glasses

“…[5][6][7][8][9] Experimentally, only a few electron microscopy and atomic probe tomography investigations, which provide the spatial resolution necessary for resolving nanoscale features, have been devoted to directly investigate the structure and chemistry of individual shear bands. [10][11][12][13][14] Using scanning transmission electron microscopy (STEM) annular dark field (ADF) imaging, Maaß et al observed a reduction in scattering power at the core of shear bands suggesting spatially localized free volume, [10] while Rösner et al observed alternating scattering power along shear bands, which have been associated with local density fluctuations. [11,12] Chen et al [15] and Yan et al [16] showed nanocrystallization after shear banding of metallic glasses by high-resolution TEM.…”

“…[ 5–9 ] Experimentally, only a few electron microscopy and atomic probe tomography investigations, which provide the spatial resolution necessary for resolving nanoscale features, have been devoted to directly investigate the structure and chemistry of individual shear bands. [ 10–14 ]…”