Molecular dynamics study of medium-range order in metallic glasses

Likhachev, V. A.; Mikhailin, A. I.; Zhigilei, Leonid V.

doi:10.1080/01418619408242222

Cited by 24 publications

(14 citation statements)

References 19 publications

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“…regular face-sharing tetrahedra) have been also proposed as the basic building blocks in amorphous metals, we also analize them. We define a regular tetrahedron as four neighbor atoms whose relative distances differ by less than 0.55 % [20]. During the simulated quench, the heat capacity C P presents a clear discontinuity at T g ∼ 750 K, which agrees well with the experimental glass transition temperature estimated for pure nickel [21].…”

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confidence: 72%

Structure and Stability of an Amorphous Metal

Fuente

Soler

1998

Phys. Rev. Lett.

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Using molecular dynamics simulations, with a realistic many-body embedded-atom potential, and a novel method to characterize local order, we study the structure of pure nickel during the rapid quench of the liquid and in the resulting glass. In contrast with previous simulations with pair potentials, we find more crystalline order and fewer icosahedra for slower quenching rates, resulting in a glass less stable against crystallization. It is shown that there is not a specific amorphous structure, only the arrest of the transition from liquid to crystal, resulting in small crystalline clusters immersed in an amorphous matrix with the same structure of the liquid.PACS numbers: 61.43. Fs, 61.43.Bn, 81.40.Ef The detailed knowledge of the atomic structure is essential to understand the special properties of amorphous materials. There seems to be general agreement in that the basic process underlying the glass transition is the arrest of structural relaxations [1], but it is not clear to what extent this leads to new structural units. Very different structural models have been proposed [2], and some of them assume that the glass structure is essentially different from those of the liquid and the crystal. For close-packed systems, the icosahedron has been largely proposed as a characteristic configuration, which becomes predominant during liquid quenching. Another example is the polycluster model [3], in which the amorphization proceeds by the nucleation and growth of amorphous clusters within the liquid.However, like in liquids and defective solids, the lack of atomic periodicity makes the experimental determination of the structure a largely unsolved problem. Therefore, molecular dynamics simulations offer an invaluable complementary tool, although the simulated times are generally much shorter than the experimental quenches. A common strategy is to study model systems with simple interactions, hoping that they will describe qualitatively the properties of real glasses. Thus, systems simulated with pair potentials show an increase of icosahedra during liquid cooling [4][5][6][7]. However, the structural properties depend strongly on the type of interatomic potential used [8], and some simulations indicate that the formation of icosahedra decreases when many-body effects or nonadditivity are included [9]. Therefore, it is questionable to what extent these results can be extrapolated to real glasses.An alternate strategy is to focus on systems, like pure metals, whose natural relaxation times are so short that they can be actually simulated in the limit between glass formation and crystallization. Within this approach we show in this work that, in the case of a pure metal, there is no specific amorphous structure different from that of the liquid and the crystal, but only the arrest of the transition from one to the other. We also study the stability of the glass and, in contrast with recent works [4,10], show that it is more stable when quenched faster.Although the experimental quenching rates required to form thei...

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confidence: 72%

Structure and Stability of an Amorphous Metal

Fuente

Soler

1998

Phys. Rev. Lett.

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“…A mass of 100 daltons is attributed to each molecule. An amorphous molecular solid prepared by melting of a close packed crystal and subsequent quenching from the melt 54 is used in the simulation. 21 A schematic sketch of the simulation setup is shown in Fig.…”

Section: Simulation Setupmentioning

confidence: 99%

Microscopic mechanisms of laser ablation of organic solids in the thermal and stress confinement irradiation regimes

Zhigilei

Garrison

2000

Journal of Applied Physics

406

480

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The results of large-scale molecular dynamics simulations demonstrate that the mechanisms responsible for material ejection as well as most of the parameters of the ejection process have a strong dependence on the rate of the laser energy deposition. For longer laser pulses, in the regime of thermal confinement, a phase explosion of the overheated material is responsible for the collective material ejection at laser fluences above the ablation threshold. This phase explosion leads to a homogeneous decomposition of the expanding plume into a mixture of liquid droplets and gas phase molecules. The decomposition proceeds through the formation of a transient structure of interconnected liquid clusters and individual molecules and leads to the fast cooling of the ejected plume. For shorter laser pulses, in the regime of stress confinement, a lower threshold fluence for the onset of ablation is observed and attributed to photomechanical effects driven by the relaxation of the laser-induced pressure. Larger and more numerous clusters with higher ejection velocities are produced in the regime of stress confinement as compared to the regime of thermal confinement. For monomer molecules, the ejection in the stress confinement regime results in broader velocity distributions in the direction normal to the irradiated surface, higher maximum velocities, and stronger forward peaking of the angular distributions. The acoustic waves propagating from the absorption region are much stronger in the regime of stress confinement and the wave profiles can be related to the ejection mechanisms.

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“…This interatomic distance appears in the octahedral atomic configuration characteristic of the close-packed crystals but is not typical for tetrahedral clusters responsible for the short-range order in one-component noncrystalline structures. 53 Thus, as soon as material melts, the atoms tend to escape from this interatomic distance-octahedral configurations disappear and a broad second peak corresponding to the interatomic distances found in clusters with local tetrahedral and icosahedral short-range order 54,55 develops.…”

Section: E Real-space Correlationsmentioning

confidence: 99%

Time-resolved diffraction profiles and atomic dynamics in short-pulse laser-induced structural transformations: Molecular dynamics study

2006

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The diffraction profiles and density correlation functions are calculated for transient atomic configurations generated in molecular dynamics simulations of a 20 nm Au film irradiated with 200 fs laser pulses of different intensity. The results of the calculations provide an opportunity to directly relate the detailed information on the atomic-level structural rearrangements available from the simulations to the diffraction spectra measured in time-resolved x-ray and electron diffraction experiments. Three processes are found to be responsible for the evolution of the diffraction profiles. During the first several picoseconds after the laser excitation, the decrease of the intensity of the diffraction peaks is largely due to the increasing amplitude of thermal atomic vibrations and can be well described by the Debye-Waller factor. The effect of thermoelastic deformation of the film prior to melting is reflected in shifts and splittings of the diffraction peaks, providing an opportunity for experimental probing of the ultrafast deformations. Finally, the onset of the melting process results in complete disappearance of the crystalline diffraction peaks. The homogeneous nucleation of a large number of liquid regions throughout the film is found to be more effective in reducing long-range correlations in atomic positions and diminishing the diffraction peaks as compared to the heterogeneous melting by melting front propagation. For the same fraction of atoms retaining the local crystalline environment, the diffraction peaks are more pronounced in heterogeneous melting. A detailed analysis of the real space correlations in atomic positions is also performed and the atomic-level picture behind the experimentally observed fast disappearance of the correlation peak corresponding to the second nearest neighbors in the fcc lattice during the laser heating and melting processes is revealed.

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Molecular dynamics study of medium-range order in metallic glasses

Cited by 24 publications

References 19 publications

Structure and Stability of an Amorphous Metal

Structure and Stability of an Amorphous Metal

Microscopic mechanisms of laser ablation of organic solids in the thermal and stress confinement irradiation regimes

Time-resolved diffraction profiles and atomic dynamics in short-pulse laser-induced structural transformations: Molecular dynamics study

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