Mechanisms of void shrinkage in aluminium

Zhang, Zezhong; Li, Tianyu; Smith, Andrew; Medhekar, Nikhil V.; Nakashima, Philip; Bourgeois, Laure

doi:10.1107/s1600576716010657

Cited by 18 publications

(15 citation statements)

References 46 publications

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“…Often the reaction within the thin TEM specimen differs from that in the bulk, both due to the surface effect and the electron irradiation. Electron irradiation indeed can substantially lower the energy barrier for diffusion of vacancies, as we quantitatively measured in our recent study of in situ annealing of voids in aluminium [68].…”

Section: Discussionsupporting

confidence: 59%

“…In general, a vacancy has a lower formation energy at the surface than in the bulk, which leads to a vacancy flux from the surface to the bulk. Diffusion calculations using Fick's equations similar to what was used in our previous work [68] suggest that such a vacancy flux can be significant for an ultra-thin sample at a temperature higher than 100 • C, as was the case for in situ annealing experiments. The fact that small GP zones shrink during in situ annealing is an indication of such vacancy flux (see [46,45] before transforming into HCP γ / γ ( 67 at.% Ag) [18,19].…”

Section: Discussionmentioning

confidence: 72%

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The bi-layered precipitate phase ζ in the Al-Ag alloy system

et al. 2017

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The Al-Ag system is thought to be a well-understood model system used to study diffusional phase transformations in alloys. Here we report the existence of a new precipitate phase, ζ, in this classical system using scanning transmission electron microscopy (STEM). The ζ phase has a modulated structure composed of alternative bilayers enriched in Al or Ag.Our in situ annealing experiments reveal that the ζ phase is an intermediate precipitate phase between GP zones and γ . First-principles calculations show that ζ is a local energy minimum state formed during Ag clustering in Al. The layered structure of ζ is analogous to the well-known Ag segregation at the precipitate-matrix interfaces when Ag is microalloyed in various aluminium alloys.

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Section: Discussionsupporting

confidence: 59%

Section: Discussionmentioning

confidence: 72%

The bi-layered precipitate phase ζ in the Al-Ag alloy system

et al. 2017

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“…In order to examine nucleation of the θ′ phase at high spatial and temporal resolutions, we performed in situ heating experiments in the transmission electron microscope (TEM). This approach has recently been successful in characterising the evolution of precipitates embedded in a crystalline matrix at near atomic scale [23][24][25] . Using this method we achieved high nucleation rates of the θ′ phase as well as of a new precipitate phase (called η′), directly on pre-existing θ″ precipitates.…”

Section: Resultsmentioning

confidence: 99%

Transforming solid-state precipitates via excess vacancies

Bourgeois

Zhang

et al. 2020

Nat Commun

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Many phase transformations associated with solid-state precipitation look structurally simple, yet, inexplicably, take place with great difficulty. A classic case of difficult phase transformations is the nucleation of strengthening precipitates in high-strength lightweight aluminium alloys. Here, using a combination of atomic-scale imaging, simulations and classical nucleation theory calculations, we investigate the nucleation of the strengthening phase θ′ onto a template structure in the aluminium-copper alloy system. We show that this transformation can be promoted in samples exhibiting at least one nanoscale dimension, with extremely high nucleation rates for the strengthening phase as well as for an unexpected phase. This template-directed solid-state nucleation pathway is enabled by the large influx of surface vacancies that results from heating a nanoscale solid. Template-directed nucleation is replicated in a bulk alloy as well as under electron irradiation, implying that this difficult transformation can be facilitated under the general condition of sustained excess vacancy concentrations.

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“…However, according to previous reports, the stable nuclei are supposed to evolve from the vacancies that were induced by the intense electron beam irradiation. 12 Interestingly, the voids did not remain stationary. Instead, anisotropic void growth along one direction was observed ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…11 These voids are three-dimensional clusters of vacancies, which evolve through capturing or emitting vacancies on the void surfaces. 12,13 In most cases, one would try to suppress void formation because they tend to induce deleterious effects and cause structural failure. 13 There are, however, specific cases in which void formation is beneficial and can be used for the fabrication of nanostructures.…”

Section: Introductionmentioning

confidence: 99%

Real-time atomic scale observation of void formation and anisotropic growth in II–VI semiconducting ribbons

et al. 2017

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Void formation in semiconductors is generally considered to be deteriorating. However, for some systems, void formation and evolution are beneficial and can be used for the fabrication of novel nanostructures. In either scenario, the understanding of void formation and evolution is of both scientific and technical high importance. Herein, using ZnS ribbons as an example, we report real-time observations of void formation and the kinetics of growth at the nano- and atomic scales upon heating. Direct imaging reveals that voids, created by a focused electron beam in wurtzite (WZ) ribbons, have a rectangular shape elongated along the <0001> direction. The voids are enclosed by low-surface-energy planes including {01-10} and {2-1-10}, with minor contribution from the higher-energy {0001} planes. Driven by thermodynamics to minimize surface energy, the voids grow straight along the [000±1] directions, exhibiting a strong anisotropy. Occasionally, we observe oscillatory kinetics involving periodic void growth and shrinkage, likely due to the fluctuation of the local chemical potential leading to a transitional kinetic state. We also reveal that the morphology and growth kinetics of voids are highly structure-dependent. Real-time observation during void growth through the complex WZ-zinc blende (ZB)-WZ structure shows that the void, with an initial elongated rectangular morphology in the WZ domain, transforms into a different shape, dominated by the {110} surfaces, after migrating to a domain of the ZB structure. However, when the void moves from the ZB to the WZ domain, it transforms back into a rectangular shape followed by fast growth along the [0001] direction. Our experimental results, together with density functional theory (DFT) calculations, provide valuable insights into the mechanistic understanding of void formation and evolution in semiconductors. More importantly, our study may shed light on new pathways for the morphological modulation of nanostructures by utilizing the intrinsic anisotropy of void evolution in WZ semiconductors.

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Mechanisms of void shrinkage in aluminium

Cited by 18 publications

References 46 publications

The bi-layered precipitate phase ζ in the Al-Ag alloy system

The bi-layered precipitate phase ζ in the Al-Ag alloy system

Transforming solid-state precipitates via excess vacancies

Real-time atomic scale observation of void formation and anisotropic growth in II–VI semiconducting ribbons

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