Dislocation multi-junctions and strain hardening

Bulatov, Vasily V.; Hsiung, L.M.; Tang, Meijie; Arsenlis, A.; Bartelt, M. C.; Cai, Wei; Florando, J.N.; Hiratani, Masato; Rhee, Min Suk; Hommes, Gregg; Pierce, Tim; Rubia, T. Dı́az de la

doi:10.1038/nature04658

Cited by 285 publications

(148 citation statements)

References 15 publications

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“…This is critical in producing very high strain hardening. Other sessile dislocation structures that may contribute to strain hardening include dislocation jogs [31] and multiple junctions [32]. However, it was reported that experimentally observed latent hardening does not correlate with jog formation [27].…”

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confidence: 99%

Strong Strain Hardening in Nanocrystalline Nickel

et al. 2009

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Low strain hardening has hitherto been considered an intrinsic behavior for most nanocrystalline (NC) metals, due to their perceived inability to accumulate dislocations. In this Letter, we show strong strain hardening in NC nickel with a grain size of $20 nm under large plastic strains. Contrary to common belief, we have observed significant dislocation accumulation in the grain interior. This is enabled primarily by Lomer-Cottrell locks, which pin the lock-forming dislocations and obstruct dislocation motion. These observations may help with developing strong and ductile NC metals and alloys.

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confidence: 99%

Strong Strain Hardening in Nanocrystalline Nickel

et al. 2009

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“…Subsequent transition to deformation twinning leads to a velocity burst, and deformation twins propagate at a transonic speed. Classical dislocation theory predicts that, dislocation velocity cannot exceed the shear wave velocity [16], and with increasing dislocation velocity, dislocation self-pinning and tangling ensue, leading to stress accumulation until deformation twins nucleate [25,26]. Twin propagation velocity exceeds the shear wave velocity.…”

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confidence: 99%

Macrodeformation Twins in Single-Crystal Aluminum

et al. 2016

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Deformation twinning in pure aluminum has been considered to be a unique property of nanostructured aluminum. A lingering mystery is whether deformation twinning occurs in coarse-grained or single-crystal aluminum, at scales beyond nanotwins. Here, we present the first experimental demonstration of macro deformation twins in single-crystal aluminum formed under ultrahigh strain-rate (∼10 6 s −1 ), large shear strain (200%) via dynamic equal channel angular pressing. Deformation twinning is rooted in the rate dependences of dislocation motion and twinning, which are coupled, complementary processes during severe plastic deformation under ultrahigh strain rates.When we talk about crystal deformation, what do we actually talk about? Crystal defects [1]. Crystal defects such as dislocations (line defects) and twins (planar defects) play a critical role in plastic deformation and ultimately govern the multifarious mechanical behaviors of many crystalline materials [2,3]. While both dislocation slip and deformation twinning are dependent on an intrinsic material property -stacking fault energy [4,5] (SFE), their sensitivities to SFE differ considerably. A notable example is pure aluminum, a typical face-centered cubic (fcc) metal with high SFE (104-142 mJ m −2 ) [6], in which deformation twinning rarely occurs even deformed at low temperatures and/or at high strain rates [7,8]. This rareness of deformation twinning in such materials is normally attributed to the following two reasons: (i) a large number of slip systems in fcc metals render dislocation slip a very efficient deformation mode [9,10], and (ii) the nucleation of twinning partial dislocations require much higher shear stresses than trailing partial dislocations due to the high unstable twin fault energy [11]. Searching for macro deformation twins in pure aluminum and revealing the underlying mechanisms have been of sustained interest in the past decade.Molecular dynamics (MD) simulations first predicted that nanoscale deformation twins can nucleate under high tensile stress (2.5 GPa) and high strain rate (10 7 s −1 ) in nanograined aluminum [6,12], and subsequent experiments confirmed this prediction in nanograined aluminum films under different kinds of severe plastic deformation (SPD) [13][14][15]. One explanation was proposed based on classical dislocation theory [16]: when grain size decreases to tens of nanometers, normal dislocation activities are greatly suppressed by the high fraction of grain boundaries (GBs); as a result, deformation twinning takes over as the dominant deformation mechanism [13]. Besides nanograin size effect, many simulation and experimental studies suggest that deformation twinning prefers to occur at high strain rates in fcc metals [17,18]. This rate-dependent twinning mechanism has been corrobarated by a very recent experiment on pure aluminum with comparatively large nanograins (50-100 nm) [19]. However, there has been no solid evidence for deformation twinning in single-crystal or coarse-grained pure aluminum. It is natural ...

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“…However, a detailed analysis of the phenomenon is lacking due to the complexity of incorporating both vacancies and dislocations in a single computational framework. As a thermally activated process, the diffusion of vacancies occurs over times scales that are much longer than can be accessed by molecular dynamics [4,5], and available dislocation dynamics formulations [6][7][8][9] do not account for the nonlinear vacancy-dislocation interactions inherent to climb [3,10]. Only recently have dislocation glide and climb been simultaneously considered in the simulation of prismatic loop coarsening [11].…”

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confidence: 99%

Power-Law Creep from Discrete Dislocation Dynamics

et al. 2012

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We report two-dimensional discrete dislocation dynamics simulations of combined dislocation glide and climb leading to `power-law' creep in a model aluminum crystal. The approach fully accounts for matter transport due to vacancy diffusion and its coupling with dislocation motion. The existence of quasi-equilibrium or jammed states under the applied creep stresses enables observations of diffusion and climb over time scales relevant to power-law creep. The predictions for the creep rates and stress exponents fall within experimental ranges, indicating that the underlying physics is well captured.Comment: 5 pages, 5 figure

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Dislocation multi-junctions and strain hardening

Cited by 285 publications

References 15 publications

Strong Strain Hardening in Nanocrystalline Nickel

Strong Strain Hardening in Nanocrystalline Nickel

Macrodeformation Twins in Single-Crystal Aluminum

Power-Law Creep from Discrete Dislocation Dynamics

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