Langevin model for real-time Brownian dynamics of interacting nanodefects in irradiated metals

Dudarev, S. L.; Gilbert, Mark R.; Arakawa, Kazuto; Mori, Hirotarô; Yao, Zhongwen; Jenkins, M. L.; Derlet, P. M.

doi:10.1103/physrevb.81.224107

Cited by 71 publications

(52 citation statements)

References 62 publications

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“…Any correlation arising from their interaction may be eliminated by analyzing the center of massx, defined here to be the mean of the two kink positions,x = (x (1) + x (2) )/2. It may be shown 24,25 that such a quantity is independent of any interaction, and it yields a diffusion constant one half that of a free kink, D kink /2. Thus we construct from the two kink positions a single time series {x n∆t }, n = 0, 1, ...N for the center of mass to ensure such correlation effects do not affect our results.…”

Section: Molecular Dynamics Simulation Of Thermally Fluctuating DImentioning

confidence: 99%

Theory and simulation of the diffusion of kinks on dislocations in bcc metals

et al. 2013

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Isolated kinks on thermally fluctuating (1/2) 111 screw, 100 edge and (1/2) 111 edge dislocations in bcc iron are simulated under zero stress conditions using molecular dynamics (MD). Kinks are seen to perform stochastic motion in a potential landscape that depends on the dislocation character and geometry, and their motion provides fresh insight into the coupling of dislocations to a heat bath. The kink formation energy, migration barrier and friction parameter are deduced from the simulations. A discrete Frenkel-Kontorova-Langevin (FKL) model is able to reproduce the coarse grained data from MD at ∼10 −7 of the computational cost, without assuming an a priori temperature dependence beyond the fluctuation-dissipation theorem. Analytic results reveal that discreteness effects play an essential rôle in thermally activated dislocation glide, revealing the existence of a crucial intermediate length scale between molecular and dislocation dynamics. The model is used to investigate dislocation motion under the vanishingly small stress levels found in the evolution of dislocation microstructures in irradiated materials.Dislocation motion is limited by two general processes, the formation and migration of kinks and pinning by impurities and other defects 1 . In this paper we investigate the motion of kink-limited screw and edge dislocations in bcc Fe, where the kink formation energy is much larger than the thermal energy. To obtain dislocation motion on the time-scales accessible to molecular dynamics (MD) simulations some researchers have resorted to inducing kink formation by applying stresses some six orders of magnitude greater than those pertaining experimentally 2,3 .But dislocation core structures and Peierls barriers are known to be highly stress-dependent 4 , making it difficult to relate simulation to the vanishingly low stress conditions found in thermally activated evolution of dislocation microstructures.To avoid the problem of nucleating kinks in MD simulations we use periodic boundary conditions which enforce the existence of an isolated kink on each dislocation line in the supercell. This allows us to study the detailed dynamics of kink migration in isolation, a crucial and previously unexplored aspect of kink-limited dislocation motion, as seperate from the kink nucleation process. Under no applied stress, kinks are seen to undergo stochastic motion in a potential landscape that varies with the dislocation character and Burgers vector. A coarse graining procedure is introduced, that facilitates statistical analysis yielding many properties of the kink motion, and which provides physical insight into the coupling of dislocations to the heat bath. In particular, the friction parameter for a dislocation is found to be temperature-independent, contradicting decades of theoretical work since Liebfried 5 . But this temperature-independence is seen in many other investigations of dislocations 2,3,6 with a large lattice resistance and in the stochastic motion of point defects 8,9 , although to the best of our ...

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Section: Molecular Dynamics Simulation Of Thermally Fluctuating DImentioning

confidence: 99%

Theory and simulation of the diffusion of kinks on dislocations in bcc metals

et al. 2013

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“…These energies vary from a fraction of an eV to several eV [1,2]. The energy scales of elastic interactions between defects are similar, depending on the size of defects and the distance between them [3,4]. Whereas the spectrum of activation energies for 15 reactions between defects is discrete, the energies of elastic interactions are distributed continuously.…”

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“…Langevin dynamics simulations of mobile elastically interacting nano-defects [3,4] show that these interactions strongly influence the evolution of microstruc-40 ture, leading to trapping of defects, and giving rise to defect clustering and the formation of rafts of defects. Rafts of defects are routinely observed experimentally in materials exposed to irradiation [20,21,22,23,24,25,26].…”

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Elastic interactions between nano-scale defects in irradiated materials

Dudarev

2017

Acta Materialia

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Closed form expressions are derived for the energy of elastic interaction between dislocation loops, and between dislocation loops and vacancy clusters, to enable simulations of elastically biased microstructural evolution of irradiated materials. The derivations assume the defects are separated by distances greater than their size. The resulting expressions are well suited for real-space simulations of microstructural evolution involving thousands of elastically interacting defects in 3D. They play a similar role to interatomic potentials in molecular dynamics simulations.

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“…The resulting data can be deployed as an input for the theoretical models of long time evolution of damaged material. 3,14,33,34 It was shown that both the SIAs and the vacancy loops have high one-dimensional (1D) mobility along close-packed crystal directions in bcc crystals. 10,31,32 The small clusters can switch their propagation direction between equivalent directions, which result in the three-dimensional (3D) diffusion at elevated temperatures.…”

Section: Introductionmentioning

confidence: 99%

Radiation-induced damage and evolution of defects in Mo

et al. 2011

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The formation of defects in bcc Mo lattice as a result of 50-keV Xe bombardment is studied via atomistic simulation with an interatomic potential developed using the force-matching ab initio based approach. The defect evolution in the cascade is described. Diffusion and interaction of interstitials and vacancies are analyzed. Only small interstitial atom clusters form directly in the cascade. Larger clusters grow only via aggregation at temperatures up to 2000 K. Stable forms of clusters demonstrate one-dimensional diffusion with a very high diffusion coefficient and escape quickly to the open surface. Point vacancies have much lower diffusivity and do not aggregate. The possibility of a large prismatic vacancy loop formation near the impact surface as a result of fast recrystallization is revealed. The mobility of the vacancy dislocation loop segments is high, however, the motion of the entire loops is strongly hindered by neighbor point defects. This paper explains the existence of the large prismatic vacancy loops and the absence of the interstitial loops in the recent experiments with ion irradiation of Mo foils.

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Langevin model for real-time Brownian dynamics of interacting nanodefects in irradiated metals

Cited by 71 publications

References 62 publications

Theory and simulation of the diffusion of kinks on dislocations in bcc metals

Theory and simulation of the diffusion of kinks on dislocations in bcc metals

Elastic interactions between nano-scale defects in irradiated materials

Radiation-induced damage and evolution of defects in Mo

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