On the shear-affected zone of shear bands in bulk metallic glasses
Introduction
Metallic glasses (MGs) are principally of great interest as structural materials since they exhibit high strength and hardness. However, most MGs lack ductility, especially under tension where zero ductility prevails. However, in recent years progress has been made in developing bulk metallic glasses (BMGs) exhibiting respectable ductility during cold rolling, bending and compression tests. Upon inhomogeneous deformation, that is at low temperatures and high stresses, the plasticity is manifested by a macroscopic sliding along a localized region called a shear band (SB) having a typical thickness of about 15 nm, when tilted upright (edge-on) [[1], [2], [3]]. It has been found that such SBs contain alternating density changes accompanied by structural changes in the medium range order (MRO) [[3], [4], [5], [6]]. The current understanding of how mesoscopic SBs evolve from shear transformation zones (STZs), which are regarded as the main carriers for plasticity in metallic glasses [7], is that alignments of Eshelby-like quadrupolar stress-field perturbations lead to percolation and thus to SB formation [6,8]. The formation of a SB upon deformation creates an interface between the SB and the matrix. To maintain cohesion at the interface atoms need to be rearranged in the matrix, which consequently should also affect the adjacent matrix regions. Indeed, recent publications report on the existence of so-called shear band affected zones (SBAZs) [[9], [10], [11], [12]]. To address the relation between the structure of amorphous materials in terms of MRO and their mechanical behavior in more detail, the immediate environment of SBs in BMGs was investigated using fluctuation electron microscopy (FEM) to extract the local information on MRO [[13], [14], [15]]. FEM contains information about the four-body correlation of atom pairs (pair-pair correlation function) g4(r1,r2,|r|,θ) yielding information about the MRO (cluster size and volume fraction) in amorphous materials [15,16]. The obtained MRO profiles measured across SBs from tensile and compressive sides of 3-point bending tests display the impact of the local stress state on the MRO and thus shed more light on the lateral extension of deformation in SB environments.
Section snippets
Methods
FEM and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) were performed with a Thermo Fisher Scientific FEI Themis 300 G3 transmission electron microscope (TEM) operated at 300 kV. Nanobeam diffraction patterns (NBDPs) were acquired with parallel illumination using probe sizes of 1.3 and 1.6 nm at full width half maximum (FWHM) in μProbe-STEM mode operated at spotsize 8 with a 50 μm C2 aperture giving a semi-convergence angle of 0.58–0.8 mrad. The probe size
Results
3-point bending test of notched bars were carried out (see supplementary video in Appendix A). A more detailed description is given in Ref. [23]. During such deformation tests, the area around the notch is dominated by tensile strain whereas the side opposite to the notch is mainly under compressive strain. In this paper these specific regions are referred to as the tensile and compressive sides, respectively. FIB lamellae containing SBs from each side (tensile and compressive) of the deformed
Discussion
In the following we discuss the robustness of this analysis.
Conclusions
Fluctuation electron microscopy revealed a detailed structural picture of the interplay between deformation and MRO structure obtained from two representative BMGs (Pd40Ni40P20 and Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105)) performed under 3-point bending conditions. (i) Prior to deformation, the amount of MRO was observed to be higher for Vit105 than for Pd40Ni40P20. The degree of MRO was reduced after deformation. Profiling the MRO of shear band environments from compressive and tensile sides
CRediT authorship contribution statement
Farnaz A. Davani: Investigation, Data curation, Formal analysis, Writing - original draft. Sven Hilke: Investigation, Formal analysis, Software, Writing - review & editing. Harald Rösner: Conceptualization, Methodology, Writing - review & editing, Validation, Supervision. David Geissler: Methodology, Software, Writing - review & editing. Annett Gebert: Supervision, Writing - review & editing, Funding acquisition. Gerhard Wilde: Writing - review & editing, Supervision, Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We gratefully acknowledge financial support by the DFG via SPP 1594 (Topological engineering of ultra-strong glasses, WI 1899/27-2 and GE 1106/11) and WI 1899/29-1 (Coupling of irreversible plastic rearrangements and heterogeneity of the local structure during deformation of metallic glasses, projekt number 325408982). Moreover, we acknowledge funding for our TEM equipment via the DFG Major Research Instrumentation Programme under INST 211/719-1 FUGG.
References (35)
- et al.
The structure of shear bands in metallic glasses
Acta Metall.
(1981) - et al.
The influence of deformation on the medium-range order of a Zr-based bulk metallic glass characterized by variable resolution fluctuation electron microscopy
Acta Mater.
(2019) - et al.
Density changes in shear bands of a metallic glass determined by correlative analytical transmission electron microscopy
Ultramicroscopy
(2014) - et al.
Structural processes that initiate shear localization in metallic glass
Acta Mater.
(2009) - et al.
Long range stress fields and cavitation along a shear band in a metallic glass: the local origin of fracture
Acta Mater.
(2015) - et al.
Fluctuation microscopy in the STEM
Ultramicroscopy
(2002) Circular Hough transform diffraction analysis: a software tool for automated measurement of selected area electron diffraction patterns within Digital MicrographTM
Ultramicroscopy
(2008)- et al.
Nanobeam diffraction fluctuation electron microscopy technique for structural characterization of disordered materials—application to Al88Y7Fe5Ti metallic glasses
Ultramicroscopy
(2010) - et al.
Effect of sample thickness, energy filtering, and probe coherence on fluctuation electron microscopy experiments
Ultramicroscopy
(2011) - et al.
Catastrophic stress corrosion failure of Zr-base bulk metallic glass through hydrogen embrittlement
Corrosion Sci.
(2019)
Atomic-scale mechanisms of tension-compression asymmetry in a metallic glass
Acta Mater.
Effect of stress gradient on the deformation behavior of a bulk metallic glass under uniaxial tension
Mater. Sci. Eng., A
Deformation behavior of a Zr-based bulk metallic glass under a complex stress state
Intermetallics
Effect of complex stress fields on the plastic energy accumulation in a Zr-based bulk metallic glass
Phys. B Condens. Matter
Softening and dilatation in a single shear band
Acta Mater.
Atomic-scale origin of shear band multiplication in heterogeneous metallic glasses
Scripta Mater.
Thickness of shear bands in metallic glasses
Appl. Phys. Lett.
Cited by (22)
Research progress on the shear band of metallic glasses
2023, Journal of Alloys and CompoundsCharacterization of bulk metallic glasses by microscratch test under Rockwell C diamond indenter and progressive normal load
2023, Engineering Fracture MechanicsOutside-in disintegration of medium-range order in nano metallic glasses during torsion deformation revealed by molecular dynamics simulations
2022, Journal of Non-Crystalline SolidsCitation Excerpt :Therefore, it is of great significance to examine the detailed yielding process of MROs in MGs and its underlying mechanism during torsion deformation. Although it is reported in recent years that the MROs in bulk MGs could be analyzed by employing advanced experimental equipment such as four-dimensional scanning transmission electron microscopy and variable resolution fluctuation electron microscopy [16–19]. Unfortunately, the MRO structures in nano MGs, especially its dynamic evolution, are difficult to characterize by conventional experiment techniques such as microscopy or diffraction measurements [11,20].
Correlation between phase transformation and surface morphology under severe plastic deformation of theAl<inf>87</inf>Ni<inf>8</inf>La<inf>5</inf> amorphous alloy
2022, Journal of Non-Crystalline SolidsCitation Excerpt :Deformation often results in the branching of shear bands [9,22]. Such branches of shear bands do not always penetrate the surface, so they often remain undetected [13]. More recent studies have shown that the structure of shear bands and their vicinity iscomplex, and changes of the amorphous phase structure can propagate at large distances from a shear band.
Impact of cryogenic cycling on tracer diffusion in plastically deformed Pd<inf>40</inf> Ni<inf>40</inf> P<inf>20</inf> bulk metallic glass
2021, Acta MaterialiaCitation Excerpt :Recent investigations by digital image correlation revealed that the shear band formation during rolling shows a local stick-slip behaviour [27] on the level of the individual shear band. There is no clear evidence about the plastic shear distribution and shear bands through the samples processed by HPT [22]; one may imagine that the whole HPT-processed sample consists of shear bands and shear band-affected zones, that have been found to extend over about 1 micrometer in thickness along the shear bands [17]. It was argued that HPT processing of a bulk metallic glass induces a rejuvenated amorphous structure characterized by an increased average free volume in comparison to the as-cast material below the glass transition temperature, as it was indicated by the DSC measurements and observed local strain softening within rejuvenated regions that were distributed heterogeneously [28].