Structural investigation of cold-rolled metallic glasses using positron annihilation methods

Chen, H. S.; Chuang, S. Y.

doi:10.1063/1.88483

Cited by 54 publications

(19 citation statements)

References 3 publications

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“…[4][5][6][7][8][9][10][11][12] The functional dependence of the disordering process on these quantities is a fortiori unknown. It seems clear, though, that the process is accompanied by shear-induced dilatation, [13][14][15][16] a phenomenon that has been known for years in the deformation of soils that consist of randomly packed grains. 17,18 One expects deformation-induced disordering to occur during homogeneous deformation as well.…”

Section: Introductionmentioning

confidence: 99%

Creation and annihilation of free volume during homogeneous flow of a metallic glass

Heggen

Spaepen

Feuerbacher

2004

Journal of Applied Physics

172

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Bulk samples of Pd41Ni10Cu29P20 glass were tested at constant true stress (20–636MPa) in compression at 550, 555, and 565K to study the transition from steady-state creep at low stress to deformation-induced softening at high stress. In the high-stress regime strongly accelerating creep was observed. All deformation was homogeneous. The activation volume was 106Å3. The isoconfigurational activation energy was 9.03±0.64eV. The disordering rate is proportional to the applied power density (stress×strain rate). The disordering process is inefficient in energy and in the production of free volume.

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Section: Introductionmentioning

confidence: 99%

Creation and annihilation of free volume during homogeneous flow of a metallic glass

Heggen

Spaepen

Feuerbacher

2004

Journal of Applied Physics

172

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“…Free volume change induced by plastic deformation has been investigated by using various techniques such as positron annihilation, 9,10) direct density measurement, 11,12) TEM and SEM observation, 2,3) fluctuation electron microscopy, 13) and so on. However, the experimental techniques have inherent limitations in spatial and temporal resolutions; and most tests have to be performed after sample failure.…”

Section: Introductionmentioning

confidence: 99%

Free Volume Evolution in Metallic Glasses Subjected to Mechanical Deformation

2007

Mater. Trans.

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We define the Turnbull-Cohen free volume as the critical excess of the Voronoi volume of an atom less its core volume. Using molecular dynamics simulation we calculated the free volume change in two model binary metallic glasses undergoing tension and shear deformation. We show that the free volume change is an integral part of the deformation process; and the shear localization manifested as a shear band is directly related to the inhomogeneous distribution of the free volumes. Shear band formation may consist of two stages: the initial free volume production in the amorphous solids and the liquefaction of the regions with accumulated deformation strains. We show, for the first time, the formation of voids and the ''vein'' patterns on fracture surfaces at atomic scales; they are the combined result of the free volume change and loading and sample conditions.

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“…73) Positron annihilation studies of deformed bulk Zr-glasses support this view. 77) By contrast, earlier work on cold-rolling of metallic glasses suggested that the rolling would cause a densification through local regrouping of atoms. 78) In a Mössbauer-study of coldrolled Fe-Ni-glasses 79) it was found that the deformation following cold rolling was not only confined to shear-bands, but distributed throughout the volume of the sample.…”

Section: Crystallization Reactions During Intense Deformationmentioning

confidence: 83%

Nanocrystallization Reactions in Amorphous Aluminum Alloys

et al. 2003

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Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk volumes comprised of a high density (10 21 -10 23 m À3 ) of nanocrystals (7-20 nm) within an amorphous matrix. The primary crystallization kinetics in response to the annealing and the deformation of amorphous Al alloys are assessed in specific sample types and selected thermal treatments to evaluate primary nanocrystallization reactions. All amorphous Al alloy compositions are hypereutectic so that the initial phase selection of primary Al proceeds at a reduced driving free energy compared to thermodynamically favored intermetallic phases. Differential scanning calorimetry (DSC) studies on powders and melt spun ribbon (MSR) samples based upon thermal cycling and annealing below the glass transition, T g , demonstrate a strong sensitivity of the primary crystallization onset and reaction enthalpy to thermal history and the as-quenched state. Microcalorimetry investigations and careful analysis of nanocrystal size distributions for Al 92 Sm 8 MSRs following sub-T g anneals reveal a partial nanocrystallization reaction resulting from a transient, decaying nucleation rate and a limited supply of heterogeneous nucleation sites. While crystallization is generally thought of as a thermally activated process, it can also be induced in response to external forcing such as irradiation or mechanical alloying. Intense deformation of amorphous Al 88 Y 7 Fe 5 MSR, for example, yields a distribution of Al-nanocrystallites in the amorphous matrix without thermal annealing. Moreover, the results of cold-rolling experiments with melt-spun amorphous Al 85 Ni 10 Ce 5 ribbons show that the deformation process can alter the phase selection upon annealing. These results suggest that the shear process during rolling effects a local rearrangement of atoms in the amorphous matrix. The kinetics behavior highlights the important role of the as-synthesized amorphous structure, reaction pathways and transient conditions on the evolution of nanoscale microstructures during primary crystallization.

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Structural investigation of cold-rolled metallic glasses using positron annihilation methods

Cited by 54 publications

References 3 publications

Creation and annihilation of free volume during homogeneous flow of a metallic glass

Creation and annihilation of free volume during homogeneous flow of a metallic glass

Free Volume Evolution in Metallic Glasses Subjected to Mechanical Deformation

Nanocrystallization Reactions in Amorphous Aluminum Alloys

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