Mechanical behavior of shear bands and the effect of their relaxation in a rolled amorphous Al-based alloy

Jiang, W. H.; Pinkerton, F. E.; Atzmon, Michael

doi:10.1016/j.actamat.2005.04.003

Cited by 145 publications

(79 citation statements)

References 48 publications

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“…For the present 'ductile' CuZr glass with smaller G/B ratio, the correlation is relatively weaker which indicates that shear could be the dominating deformation mode [35]. While it is most likely to find brittle behaviors in stronger shear-dilatation correlation glass (with bigger G/B ratio) since the great propensity to nucleate cavitation (or TTZ) via shear-induced dilatation, which has been proposed as a brittle fracture mechanism in MGs [33,35,31,18,17,34]. as demonstrated by Fig.…”

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confidence: 91%

“…The microscopic scenario is that the STZ operations redistribute stress spatially which usually leads to the creation of free volume via atomic-scale dilatation [21,1]. So that local structural dilatation [19,30,31], density change [27,28], and even nanovoids [32,33,21,34] have been observed within the shear bands of MGs. Although the concept of shear-dilatation correlation is widely accepted in the glass community, and various experiments and simulations have indicated STZ and cavitation as important deformation and fracture mechanisms of glassy alloys [33,35,31,18,17,34], there still lacks a direct microscopic evidence and no quantitative relationship established for such an intimate correlation.…”

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Direct atomic-scale evidence for shear–dilatation correlation in metallic glasses

et al. 2016

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Direct atomic-scale evidence is presented for the shear-dilatation correlation in metallic glasses via molecular dynamics and first-principles calculations. A quantitative parabolic relationship is established between the atomic local shear and hydrostatic volumetric strains by carrying out statistical analysis on a deformed glass model. The correction is further verified by density functional theory. Our atomistic demonstration of shear-dilatation correlation collaborates with the experimentally observed a few percent volume change in shear bands. It brings quantitative insights into the unique correlation between shear transformation and cavitation in metallic glasses.© 2015 Elsevier Ltd. All rights reserved.Metallic glasses (MGs) are a category of promising high strength structural materials with many other superior physical and chemical properties [1]. The deformation mechanisms of such amorphous solid state are in sharp contrast with their crystalline counterparts since there are no long-range atoms packing pattern in MGs [2,3]. No conventional mechanisms, such as ordinary dislocation plasticity or deformation twinning in crystals, exist in MGs which can carry plastic deformation. Therefore MGs usually suffer from the notorious catastrophic failure with a strong strain localization (shear banding) phenomenon [4,5].Several models have been proposed to rationalize the inelastic deformation of MGs, which include free volume [6], shear transformation zone (STZ) [7][8][9], cooperative shear model (CSM) [10,11], flow unit [12], vibrational soft spot [13], shear-diffusive transformation [14,15], and our recently proposed tensile transformation zone (TTZ) [16][17][18]. All of these models are based on the local structural rearrangement of atoms via the interplay of atomic-scale shear and dilation/contraction in MGs [19][20][21][22][23][24]. Among them, Argon's STZ model involves local rearrangement of a cluster of atoms undergoing a stress-driven, and thermally activated shear distortion [25,23,24]. Whereas Spaepen's free volume model is based on a dynamic equilibrium between the stress-assisted creation and annihilation of free volume [6]. The free volume behaviors can be regarded as dilation and contraction of local atomic environments. Since both models have been successfully adopted to describe the homogeneous and inhomogeneous flows in MGs, there should be some intrinsic correlation between shear and dilatation/compaction during deformation of glasses [21,26].Generally, shear-dilatation correlation is an intrinsic nature of deformation in amorphous alloys although local compaction is also allowed [27,28]. For example, intuitively derived law between shear strain and local dilatation has been used in constitutive modelings of MGs [29]. Shear is not necessarily the only deformation mode accommodating the local atomic rearrangement. The microscopic scenario is that the STZ operations redistribute stress spatially which usually leads to the creation of free volume via atomic-scale dilatation [21,1]. So that local ...

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Direct atomic-scale evidence for shear–dilatation correlation in metallic glasses

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“…While the shear response of amorphous solids has received a significant amount of attention in the theoretical physics and molecular simulation literature over the past decade [1-8], significantly less attention has been devoted to hydrostatic loading in such systems [9,10]. This omission appears significant since experimental studies in metallic glass (MG) and other amorphous solids reveal nanocavities [11,12] that form during or subsequent to deformation and strongly implicate cavitation in the physics of the fracture process zone, even when the fracture behavior is relatively brittle [13][14][15]. The importance of cavitation in fracture is supported by recent molecular dynamics (MD) simulations in glassy Cu 50 Zr 50 and Fe 80 P 20 [16].…”

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confidence: 93%

Cavitation in Amorphous Solids

Guan

Spector

et al. 2013

Phys. Rev. Lett.

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Molecular dynamics simulations of cavitation in a Zr 50 Cu 50 metallic glass exhibit a waiting time dependent cavitation rate. On short time scales nucleation rates and critical cavity sizes are commensurate with a classical theory of nucleation that accounts for both the plastic dissipation during cavitation and the cavity size dependence of the surface energy. All but one parameter, the Tolman length, can be extracted directly from independent calculations or estimated from physical principles. On longer time scales strain aging in the form of shear relaxations results in a systematic decrease of cavitation rate. The high cavitation rates that arise due to the suppression of the surface energy in small cavities provide a possible explanation for the quasibrittle fracture observed in metallic glasses. DOI: 10.1103/PhysRevLett.110.185502 PACS numbers: 63.50.Lm, 62.20.mm, 64.70.pe Amorphous materials, commonly termed glasses when quenched from the melt, occur in every class of material including ceramics, metals, and polymers. While the shear response of amorphous solids has received a significant amount of attention in the theoretical physics and molecular simulation literature over the past decade [1-8], significantly less attention has been devoted to hydrostatic loading in such systems [9,10]. This omission appears significant since experimental studies in metallic glass (MG) and other amorphous solids reveal nanocavities [11,12] that form during or subsequent to deformation and strongly implicate cavitation in the physics of the fracture process zone, even when the fracture behavior is relatively brittle [13][14][15]. The importance of cavitation in fracture is supported by recent molecular dynamics (MD) simulations in glassy Cu 50 Zr 50 and Fe 80 P 20 [16].Theory and simulation studies have been applied to understand this process in liquids more commonly than in glasses. Two recent studies [17,18] simulated the process of homogeneous nucleation in liquids in comparison with experimental data. These studies observed evidence of the curvature dependence of the surface energy on the measured cavitation rate, an effect that has itself been the subject of a significant amount of study [19][20][21][22]. One particularly notable contribution from simulation was the mapping out of the point at which the gas-liquid spinodal dips below the glass line and the glass must become unstable to cavitation [23].Continuum mechanics approaches to modeling the kinetics of cavitation have been developed over many years by numerous researchers [6,[24][25][26][27][28][29][30]. Often preexisting cavities are assumed to exist due to voids, inclusions, or intersections of grains, and the effect of surface energy is neglected. Various assumptions have been considered regarding the plastic constitutive behavior around the cavity [6,[24][25][26][27][28][29][30]. In these cases, because plastic and elastic energy both scale with the volume of the void, above a critical stress cavity growth becomes unbounded. Here, as in some earlier ...

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“…[19][20][21][22][23][24][25] Yokoyama et al have reported that the mechanical properties are improved by the formation of shear bands upon cold rolling in Zr-based BMG. 20) Jiang et al have reported the mechanical properties of an amorphous Al-based alloy in which nanoscale shear bands are introduced by cold rolling.…”

Section: Introductionmentioning

confidence: 99%

“…20) Jiang et al have reported the mechanical properties of an amorphous Al-based alloy in which nanoscale shear bands are introduced by cold rolling. 21) It is an interesting experiments to improve mechanical properties by microstructural modification during processing, i.e., introducing shear bands on purpose. However, previous results have problems that only thin ribbon is obtained in amorphous alloy and BMG partially fractures after cold working.…”

Section: Introductionmentioning

confidence: 99%

Microstructural Change by Friction Stir Processing in Zr-Al-Cu-Ni Bulk Metallic Glass

Takigawa

Kobata

Chung³

et al. 2007

Mater. Trans.

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Microstructural change by friction stir processing (FSP) is examined in Zr-Al-Cu-Ni bulk metallic glass. The microstructure in the friction zone (FZ) exhibits an amorphous ''band-like'' structure, and a small number of nanoscale crystalline particles are observed along the ''band-like'' structure. The change in hardness with the microstructural change is examined and it is revealed that the hardness in FZ greatly increases although the volume fraction of crystalline phase is very limited. The increasing hardness is possibly explained from the combined effect of low temperature annealing during FSP and nano-size of crystalline particles.

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Mechanical behavior of shear bands and the effect of their relaxation in a rolled amorphous Al-based alloy

Cited by 145 publications

References 48 publications

Direct atomic-scale evidence for shear–dilatation correlation in metallic glasses

Direct atomic-scale evidence for shear–dilatation correlation in metallic glasses

Cavitation in Amorphous Solids

Microstructural Change by Friction Stir Processing in Zr-Al-Cu-Ni Bulk Metallic Glass

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