Atomistic mechanisms of intermittent plasticity in metals: Dislocation avalanches and defect cluster pinning

Niiyama, Tomoaki; Shimokawa, Tomotsugu

doi:10.1103/physreve.91.022401

Cited by 20 publications

(16 citation statements)

References 43 publications

(83 reference statements)

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“…1(a); σ z (t) gradually increases by elastic deformation and abruptly drops by repeated plastic deformation, where the time-series are averaged over a 0.2 ps interval to remove thermal fluctuations. This serrated behavior is the same as the intermittent plasticity observed in previous numerical studies 21,22 , but the amplitude of the stress fluctuation decreases as N GB increases.…”

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confidence: 84%

Barrier effect of grain boundaries on the avalanche propagation of polycrystalline plasticity

Niiyama

Shimokawa

2016

Phys. Rev. B

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To investigate the barrier effect of grain boundaries on the propagation of avalanche-like plasticity at the atomic-scale, we perform three-dimensional molecular dynamics simulations by using simplified polycrystal models including symmetric-tilt grain boundaries. The cut-offs of stress-drop distributions following power-law distributions decrease as the size of the crystal grains decreases. We show that some deformation avalanches are confined by grain boundaries; on the other hand, unignorable avalanches penetrate all the grain boundaries included in the models. The blocking probability that one grain boundary hinders this system-spanning avalanche is evaluated by using an elemental probabilistic model.A new insight into crystalline plasticity has been provided from non-equilibrium physics at the beginning of the century. Discontinuous, stick-slip plastic deformation, referred to as intermittent plasticity, has been revealed as an intrinsic nature of plasticity in crystalline solids [1][2][3][4][5][6][7][8] ; the probability of a deformation event with a magnitude s follows a power-law distribution, P(s) ∝ s −β , where β is a constant. This power-law distribution is a fingerprint of the presence of non-equilibrium critical phenomena especially self-organized criticality 9,10 . A combination of acoustic emission measurements and numerical simulations using discrete-dislocation dynamics have revealed that the power-law behavior of plasticity is caused by avalanches of dislocation motions 2,6 . The acoustic emission measurements in the creep of polycrystal ices have indicated that grain boundaries (GBs), i.e., interfaces between crystal grains, can act as obstacles to the avalanches 11,12 . Louchet et al. have introduced a new concept regarding the plastic deformation of polycrystals, which is one of the most fundamental subjects in material science; polycrystal yielding occurs when the avalanche transmits across GBs and percolates through the material 13 . Thus, the elucidation of the interaction between GBs and avalanches of plasticity would advance our understanding regarding the features of plastic deformation of polycrystals, in particular, the grain size dependence of plastic yielding [14][15][16] . The interaction between single dislocations and GBs has been extensively investigated [17][18][19] , but the quantification of the interaction between avalanches of dislocations is still quite preliminary. The consequence of the avalanche statistics by GBs has been discussed through discrete-dislocation dynamics 20 . However, the dislocation-GB interaction is truly atomic-scale dynamics. Therefore, molecular dynamics (MD) simulations for this issue are desperately needed to provide a correct description and quantification of the interaction. Recently, intermittent plasticity in single crystals has been successfully reproduced by MD simulations 21,22 . However, intermittent plasticity in polycrystals remains unaddressed.In this study, by performing MD simulations with polycrystal models consisting of some symmetr...

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confidence: 84%

Barrier effect of grain boundaries on the avalanche propagation of polycrystalline plasticity

Niiyama

Shimokawa

2016

Phys. Rev. B

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“…S3e). The waiting time is defined as the difference between t 2 and t 3 , that is t = t 3 − t 2 14,19 . The jerk amplitude is defined as the height of peak in the squared derivative time series (d σ /d t ) 2 (Fig.…”

Section: Methodsmentioning

confidence: 99%

Rotatable precipitates change the scale-free to scale dependent statistics in compressed Ti nano-pillars

Pan

Wang

et al. 2019

Sci Rep

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Compressed nano-pillars crackle from moving dislocations, which reduces plastic stability. Crackling noise is characterized by stress drops or strain bursts, which scale over a large region of sizes leading to power law statistics. Here we report that this “classic” behaviour is not valid in Ti-based nanopillars for a counterintuitive reason: we tailor precipitates inside the nano-pillar, which “regulate” the flux of dislocations. It is not because the nano-pillars become too small to sustain large dislocation movements, the effect is hence independent of size. Our precipitates act as “rotors”: local stress initiates the rotation of inclusions, which reduces the stress amplitudes dramatically. The size distribution of stress drops simultaneously changes from power law to exponential. Rotors act like revolving doors limiting the number of passing dislocations. Hence each collapse becomes weak. We present experimental evidence for Ti-based nano-pillars (diameters between 300 nm and 2 μm) with power law distributions of crackling noise P( s ) ∼ s − τ with τ ∼ 2 in the defect free or non-rotatable precipitate states. Rotors change the size distribution to P( s ) ∼ exp(− s / s 0 ). Rotors are inclusions of ω-phase that aligns under stress along slip planes and limit dislocation glide to small distances with high nucleation rates. This opens new ways to make nano-pillars more stable.

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“…The intermittent plastic deformation in crystals was modeled previously using molecular dynamics [30], discrete dislocation dynamics [17,19,[31][32][33], phase field theories [34], and various mesoscopic approaches [35,36]. The results of different simulations are not fully consistent, suggesting that scaling exponents may be covering a broad range of values [18,37,38] and supporting the idea that microplasticity is not a universal critical phenomenon.…”

Section: Introductionmentioning

confidence: 96%

Variety of scaling behaviors in nanocrystalline plasticity

Zhang

Salman²,

Weiss

et al. 2020

Phys. Rev. E

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We address the question of why larger, high-symmetry crystals are mostly weak, ductile, and statistically subcritical, while smaller crystals with the same symmetry are strong, brittle and supercritical. We link it to another question of why intermittent elasto-plastic deformation of submicron crystals features highly unusual size sensitivity of scaling exponents. We use a minimal integer-valued automaton model of crystal plasticity to show that with growing variance of quenched disorder, which can serve in this case as a proxy for increasing size, submicron crystals undergo a crossover from spin-glass marginality to criticality characterizing the second order brittle-to-ductile (BD) transition. We argue that this crossover is behind the nonuniversality of scaling exponents observed in physical and numerical experiments. The nonuniversality emerges only if the quenched disorder is elastically incompatible, and it disappears if the disorder is compatible.

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Atomistic mechanisms of intermittent plasticity in metals: Dislocation avalanches and defect cluster pinning

Cited by 20 publications

References 43 publications

Barrier effect of grain boundaries on the avalanche propagation of polycrystalline plasticity

Barrier effect of grain boundaries on the avalanche propagation of polycrystalline plasticity

Rotatable precipitates change the scale-free to scale dependent statistics in compressed Ti nano-pillars

Variety of scaling behaviors in nanocrystalline plasticity

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