In situ TEM observations of reverse dislocation motion upon unloading in tensile-deformed UFG aluminium

Mompiou, Frédéric; Caillard, D.; Legros, Marc; Mughrabi, H.

doi:10.1016/j.actamat.2012.02.049

Cited by 142 publications

(70 citation statements)

References 28 publications

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“…3a and c). The above results indicate that the dislocation emission process is energetically more favorable, as shear-coupled migration is the dominating process compared with pure normal migration and that the coupled shear (i.e., β 4 0) is able to considerably enhance the dislocation emission in NC materials, which is in good agreement with the existing observations made in experiments [27,[38][39][40], MD and quasicontinuum studies [25,26].…”

Section: Resultssupporting

confidence: 81%

“…This result indicates that the coupled shear (i.e., the coupling factor β) plays an important role in enhancing the dislocation activity in nanocrystalline materials, which consist of mostly high-angle boundaries (i.e., ω4 0:26) [1]. This finding provides a possible explanation for the abundant dislocation activity observed in the experiments conducted by De Hosson et al [38,39] and Mompiou et al [27,40] for nano-grained and ultrafine-grained Al during nano-indentation or tensioning where grain boundary motions played a significant role. Since the value of β depends on the specific structure of GBs, the results obtained from Fig.…”

Section: Resultssupporting

confidence: 52%

“…[25]). Some experiments carried out by De Hosson et al [38,39] and Mompiou et al [27,40] have also shown that dislocations activity was promoted during the motion of grain boundary in bicrystal or ultrafine-grained metals and that the moving GBs acted as a source of dislocations. Most recently, Ovid'ko and Skiba [41] proposed theoretically that dislocations could emit approximately vertically from a disclinated GB fragment generated by GB sliding or migration.…”

Section: Introductionmentioning

confidence: 99%

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Enhancing dislocation emission in nanocrystalline materials through shear-coupled migration of grain boundaries

Soh

2014

Materials Science and Engineering: A

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a b s t r a c tA theoretical model has been developed to illustrate the effect of shear-coupled migration of grain boundaries on dislocation emission in nanocrystalline materials. The energy characteristics and critical shear stress τ c that is required to initiate the emission process were determined. The results obtained show that the dislocation emission can be considerably enhanced as shear-coupled migration was the dominating process; a critical coupling factor that corresponded to the minimum τ c , which led to an optimal dislocation emission, was also discovered. The proposed model has also been quantitatively validated by the existing molecular dynamics simulations.

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Section: Resultssupporting

confidence: 81%

Section: Resultssupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

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Enhancing dislocation emission in nanocrystalline materials through shear-coupled migration of grain boundaries

Soh

2014

Materials Science and Engineering: A

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“…For example, in Al, deformation twins only form sporadically under extreme conditions, such as near crack tips (high stress concentration), during ball milling at cryogenic temperature or in deformed nanocrystalline grains [17][18][19][20] . While mechanical behaviour of conventional polycrystalline Al has been studied, including pop-in effects 21 , stress-induced grain boundary migration 22 , the onset of plasticity before the first increase in repulsive force 23 , reverse dislocation motion on unloading 24 and strain ratedependent plasticity 25 , successful fabrication of high-density growth twins in Al was only recently accomplished 26,27 ; thus, the deformation behaviour of highly twinned Al remains a mystery.…”

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confidence: 99%

In situ nanoindentation study on plasticity and work hardening in aluminium with incoherent twin boundaries

et al. 2014

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Nanotwinned metals have been the focus of intense research recently, as twin boundaries may greatly enhance mechanical strength, while maintaining good ductility, electrical conductivity and thermal stability. Most prior studies have focused on low stacking-fault energy nanotwinned metals with coherent twin boundaries. In contrast, the plasticity of twinned high stacking-fault energy metals, such as aluminium with incoherent twin boundaries, has not been investigated. Here we report high work hardening capacity and plasticity in highly twinned aluminium containing abundant S3{112} incoherent twin boundaries based on in situ nanoindentation studies in a transmission electron microscope and corresponding molecular dynamics simulations. The simulations also reveal drastic differences in deformation mechanisms between nanotwinned copper and twinned aluminium ascribed to stacking-fault energy controlled dislocation-incoherent twin boundary interactions. This study provides new insight into incoherent twin boundary-dominated plasticity in high stacking-fault energy twinned metals.

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“…In nanotwinned copper, it has been postulated from the low value of the activation volume (few b 3 , compared to value of several hundreds of b 3 for typical mechanisms in coarse grained) that twin transmission is the rate controlling deformation mechanism [13]. Moreover, because lattice dislocations can easily dissociate and eventually glide inside a coher-ent twin [10], contrary to grain boundaries where they usually decompose [14,15], ductility is enhanced compared to conventional nanocrystalline (nc) metals.…”

Section: Introductionmentioning

confidence: 99%

In situ TEM study of twin boundary migration in sub-micron Be fibers

Mompiou

Legros

Ensslen³

et al. 2015

Acta Materialia

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Deformation twinning in hexagonal crystals is often considered as a way to palliate the lack of independent slip systems. This mechanism might be either exacerbated or shut down in small-scale crystals whose mechanical behavior can significantly deviate from bulk materials. Here, we show that sub-micron beryllium fibers initially free of dislocation and tensile tested in-situ in a transmission electron microscope (TEM) deform by a {1012} 1011 twin thickening. The propagation speed of the twin boundary seems to be entirely controlled by the nucleation of twinning dislocations directly from the surface. The shear produced is in agreement with the repeated lateral motion of twinning dislocations. We demonstrate that the activation volume (V) associated with the twin boundary propagation can be retrieved from the measure of the twin boundary speed as the stress decreases as in a classical relaxation mechanical test. The value of V ≈ 8.3 ± 3.3 × 10 −29 m 3 is comparable to the value expected from surface nucleation. This text is a revised version of the article published in Acta Materialia, 96 (2015) 57-65

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In situ TEM observations of reverse dislocation motion upon unloading in tensile-deformed UFG aluminium

Cited by 142 publications

References 28 publications

Enhancing dislocation emission in nanocrystalline materials through shear-coupled migration of grain boundaries

Enhancing dislocation emission in nanocrystalline materials through shear-coupled migration of grain boundaries

In situ nanoindentation study on plasticity and work hardening in aluminium with incoherent twin boundaries

In situ TEM study of twin boundary migration in sub-micron Be fibers

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