The influence of twins on the mechanical properties of nc-Al

Frøseth, A. G.; Swygenhoven, H. Van; Derlet, P. M.

doi:10.1016/j.actamat.2004.01.017

Cited by 151 publications

(107 citation statements)

References 35 publications

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“…23 At the same time, previous TEM studies proved that in Al with a grain size of 10 to 20 nm, twinning became a preferred deformation mode. 24,25 These observations suggest that in addition to the value of the stacking fault energy, the grain size also has a significant effect on the contributions of the different deformation mechanisms (dislocation glide or twinning) to plastic deformation. According to the literature, because our Ni samples have relatively high stacking fault energy and the mean grain size values are several hundreds of nanometers, the majority of twin boundaries in our samples are most probably growth twins, and the observed untwinning is a result of the interaction between gliding dislocations and pre-existing twin boundaries.…”

Section: Discussionmentioning

confidence: 86%

Microstructure and mechanical behavior of ultrafine-grained Ni processed by different powder metallurgy methods

Gubicza

Bui²,

Fellah³

et al. 2009

J. Mater. Res.

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Ultrafine-grained samples were produced from a Ni nanopowder by hot isostatic pressing (HIP) and spark plasma sintering (SPS). The microstructure and mechanical behavior of the two specimens were compared. The grain coarsening observed during the SPS procedure was moderated due to a reduced temperature and time of consolidation compared with HIP processing. The smaller grain-size and higher nickel-oxide content in the SPS-processed sample resulted in a higher yield strength. Compression experiments showed that the specimen produced by SPS reached a maximal flow stress at a small strain, which was followed by a long steady-state softening while the HIP-processed sample hardened until failure. It was revealed that the softening of the SPS-processed sample resulted from microcracking along the grain boundaries.

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Section: Discussionmentioning

confidence: 86%

Microstructure and mechanical behavior of ultrafine-grained Ni processed by different powder metallurgy methods

Gubicza

Bui²,

Fellah³

et al. 2009

J. Mater. Res.

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“…25 Recently, the role of TBs in tensile deformation of different nanocrytalline materials is investigated using molecular dynamics ͑MD͒ simulations. [26][27][28] The vicinal TBs providing dislocations sites are reported in nanocrystalline Al, in which even the presence of one atomic plane step structure can trigger dislocation activity sources. 28 This is similar to the results observed in the present work.…”

Section: -2mentioning

confidence: 99%

Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries

Cao

Wei

Mao

2007

Applied Physics Letters

162

111

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This letter addresses the issue of deformation mechanisms and mechanical tensile behavior of the twinned metal nanowires using atomistic simulations. Free surfaces are always the preferential dislocation nucleation sites in the initial inelastic deformation stage, while with further plastic deformation, twin boundary interfaces will act as sources of dislocations with the assistance of the newly formed defects. The smaller the twin boundary spacing, the higher the yielding stresses of the twinned nanowires. Twin boundaries, which serve both as obstacles to dislocation motion and dislocation sources, can lead to hardening effects and contribute to the tensile ductility. This work illustrates that the mechanical properties of metal nanowires could be controlled by tailoring internal growth twin structures. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2721367͔Due to the unique mechanical, electrical, and optical properties, materials with nanometer-sized structure have attracted a great deal of interest in the past few decades [1][2][3] Many researchers have demonstrated, through both experiments and analysis, that the structure and properties of nanowires can be quite different from those of bulk materials due to the effects of larger free surfaces. [4][5][6][7][8][9][10][11][12][13][14] Simulations reported in the previous literatures are generally defect-free and the sizes of the modeled wires are usually smaller than 6 nm. [6][7][8][9][10][11][12][13][14] Meanwhile experimentally, twins, a class of planar defects, are observed most often in single-crystal metal ͑copper, silver, and gold͒ nanowires with a ͓111͔ growth orientation. 15,16 Because twin boundaries ͑TBs͒ in nanowires will strongly affect the physical properties of nanowires, it is of great significance to investigate the details of twin structures and their roles in metal nanowires. Until now, there are still some key issues about twin related deformation which are not quite clear and need fundamental understanding. For example, what is the role of TBs in mechanical deformation? Does it act as grain boundaries or surfaces? In our recent work, the mechanical behavior of fivefold twinned nanowires is studied. 17 We found that the strengthening mechanism in the fivefold twinned nanowires is due to the TBs as obstacles to the dislocation motion. In this letter, we address the effect of TBs on inelastic deformation of the twinned nanowires using atomistic simulations.In this work we focus on twinned Cu nanowires with ͗111͘ growth orientation and nearly square cross section as indicated from the experimental observations. 15,16 The initial configuration of the twinned nanowires is constructed by repeating ⌺3 coherent twins in the ͗111͘ axis orientation. 18 Four samples are prepared for the simulations. The first one consists of two twins, the second consists of four twins, and the third contains five twins. The twin boundary spacings ͑TBSs͒ of the first, second, and third wires are 14 nm ͑sample I͒, 7 nm ͑sample II͒, and 5 nm ͑sample III͒, respect...

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“…28,29 Uniform uniaxial deformation of NT Cu has been investigated previously using both experiments and MD simulations. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Interestingly, the strength of such NT Cu was found to first increase with decreasing twin-boundary spacing (TBS), reaching a maximal strength at a critical twin thickness, then decrease with further reduced twin thickness due to a transition of deformation mechanisms from the classical Hall-Petch type strengthening to a dislocation-nucleationcontrolled softening with twin-boundary migration. 29,41 Harder and tougher materials under shock loading could offer novel applications, such as improved armor materials.…”

Section: Introductionmentioning

confidence: 99%

Shock response of nanotwinned copper from large-scale molecular dynamics simulations

Yuan

2012

Phys. Rev. B

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A series of large-scale molecular dynamics simulations have been performed to investigate the shock response of nanotwinned (NT) Cu, including shock-induced plasticity, strength behind the shock front, and spall behaviors. In this study, two configurations were investigated at an impact velocity of 600 m/s, i.e., the practical NT polycrystalline Cu with an average grain size of 10 nm and the simple NT single-crystalline Cu with an impact direction of [112]. In the NT polycrystalline Cu, the average flow stress behind the shock front first increases with decreasing twin-boundary spacing (TBS), reaching a maximum at a critical TBS, and then decreases as the TBS become even smaller. This trend of the average flow stress with decreasing TBS is due to two competitive dislocation activities under shock loading, with one being inclined to the twin boundaries (the dislocation-twin boundary intersecting) and the other parallel to the twin boundaries (detwinning with twin-boundary migration). Since voids always nucleate near the grain boundary (GB) junctions and then grow along the GBs to create spallation, no apparent correlation between the spall strength and TBS is observed in the NT polycrystalline Cu. However, the spall strengths of the NT single-crystalline Cu are found to increase with decreasing TBS. Two partial dislocation slips initiated from each twin boundary create voids at the intersections between the partial dislocation slips and twin boundaries. The smaller TBSs result in a larger number of twin boundaries and provide more nucleation sites for voids, requiring a higher tensile stress to create spallation in the NT single-crystalline Cu. These findings should provide insights for understanding the deformation physics of the NT metals subjected to shock loading.

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The influence of twins on the mechanical properties of nc-Al

Cited by 151 publications

References 35 publications

Microstructure and mechanical behavior of ultrafine-grained Ni processed by different powder metallurgy methods

Microstructure and mechanical behavior of ultrafine-grained Ni processed by different powder metallurgy methods

Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries

Shock response of nanotwinned copper from large-scale molecular dynamics simulations

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