Atomic-scale modeling of twinning disconnections in zirconium

Mackain, Olivier; Cottura, Maeva; Rodney, David; Clouet, Emmanuel

doi:10.1103/physrevb.95.134102

Cited by 34 publications

(15 citation statements)

References 66 publications

(94 reference statements)

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“…Twinning disconnections are defined as interfacial dislocations with both a Burgers vector and a step height, which exist to maintain the coherency at TBs during their migration. Using nudged elastic band calculations, a higher activation energy of homogeneous disconnection nucleation than propagation was reported [28,29], suggesting that disconnection nucleation can be the ratelimiting process of TB motion. Twinning disconnections may also nucleate heterogeneously, such as when the release of twinning disconnections from BP/PB interfaces was observed by El Kadiri et al [9].…”

Section: Introductionmentioning

confidence: 88%

Disconnection-Mediated Twin Embryo Growth in Mg

Turlo

Beyerlein

et al. 2019

SSRN Journal

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While deformation twinning in hexagonal close-packed metals has been widely studied due to its substantial impact on mechanical properties, an understanding of the detailed atomic processes associated with twin embryo growth is still lacking. Conducting molecular dynamics simulations on Mg, we show that the propagation of twinning disconnections emitted by basalprismatic interfaces controls the twin boundary motion and is the rate-limiting mechanism during the initial growth of the twin embryo. The time needed for disconnection propagation is related to the distance between the twin tips, with widely spaced twin tips requiring more time for a unit twin boundary migration event to be completed. Thus, a phenomenological model, which unifies the two processes of disconnection and twin tip propagation, is proposed here to provide a quantitative analysis of twin embryo growth. The model fits the simulation data well, with two key parameters (twin tip velocity and twinning disconnection velocity) being extracted. In addition, a linear relationship between the ratio of twinning disconnection velocity to twin tip velocity and the applied shear stress is observed. Using an example of twin growth in a nanoscale single crystal from the recent literature, we find that our molecular dynamics simulations and analytical model are in good agreement with experimental data.

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Section: Introductionmentioning

confidence: 88%

Disconnection-Mediated Twin Embryo Growth in Mg

Turlo

Beyerlein

et al. 2019

SSRN Journal

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“…The SCGBM of perfect GBs occurs through the (homogeneous) nucleation and further motion of disconnections [29,16,13,30,14]. Both processes are thermally activated.…”

Section: Shear Strain Directionsmentioning

confidence: 99%

“…Both processes are thermally activated. The SCGBM activation energy is dominated by the disconnections nucleation [13,30]. This nucleation activation energy barrier typically involves the disconnection core energies, the elastic disconnection-disconnection interaction energy and finally the Peach-Koehler energy due to the work of the shear stress.…”

Section: Shear Strain Directionsmentioning

confidence: 99%

“…Glissile disconnections have thus, Burgers vectors perpendicular to x. Following [13,30,14], assuming a linear isotropic elastic crystal (Poisson ratio ν, and shear modulus µ), the energy interaction of a migrating GB displaying two (straight) disconnections with opposite Burgers vectors ( b = b y e y + b z e z ) separated by a distance δ writes:…”

Section: Shear Strain Directionsmentioning

confidence: 99%

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Multiple coupling modes to relax shear strain during grain boundary migration

Combe

Mompiou²,

Legros³

2021

Acta Materialia

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Shear-coupled grain boundary (GB) migration is an effective plastic mechanism in absence of dislocation activity, ie. more favorably in nanocrystalline metals. For a given GB, several stress induced migration mechanisms, referred as coupling modes participate to the decrease of the elastic energy produced by the shear. They operate through the nucleation and motion of interfacial defects known as disconnections, carrying elementary shear strain characterized by their Burgers vector. However, so far, the coupling modes have been studied only under a simple shear, a situation much less complex than expected in a strained polycrystal, where multiple components of the stress tensor are present. Here we propose a more systematic investigation of the coupling modes when a composite shear is applied. This promotes the activation of new coupling modes. Using Molecular Dynamics simulations, we evidence these multiple coupling modes and the operation of their associate disconnections. Moreover, we also show that, even at low temperature, GB migration may occur by the successive occurrence of two modes: the relaxed shear appears then as an effective parameter, resulting from the combination of two operating elementary mechanisms.

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“…The SCGBM has been abundantly studied using atomistic simulations investigating for instance the dependence of the GB mobilities on the GB misorientation or structure [11,[13][14][15]. The elementary mechanisms of SCGBM have been numerically investigated on flat perfect model GB: the GB migration results from the nucleation of two mobile disconnections with opposite Burgers vectors (BV) and their migration in opposite directions [16][17][18][19][20][21][22][23]. Disconnections are GB line defects that have both step (height) and dislocation character [24].…”

mentioning

confidence: 99%