Development of an interatomic potential for the simulation of phase transformations in zirconium

Mendelev, Mikhail I.; Ackland, Graeme J.

doi:10.1080/09500830701191393

Cited by 312 publications

(223 citation statements)

References 23 publications

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“…[11] to perform ab initio calculations based on the density functional theory, an approach that has proved instrumental in unravelling dislocation core properties in various metals [10,11,[17][18][19][20][21]. We also performed atomistic simulations with the embedded atom method (EAM) potential developed by Mendelev and Ackland [22] to check the validity of our results in larger simulation cells. This potential is suitable to model screw dislocations, predicting, in particular, dissociation in a prismatic plane [23], in contrast with most other empirical potentials.…”

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confidence: 99%

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First-Principles Study of Secondary Slip in Zirconium

2014

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Although the favored glide planes in hexagonal close-packed Zr are prismatic, screw dislocations can escape their habit plane to glide in either pyramidal or basal planes. Using ab initio calculations within the nudged elastic band method, we show that, surprisingly, both events share the same thermally activated process with an unusual conservative motion of the prismatic stacking fault perpendicularly to itself. Halfway through the migration, the screw dislocation adopts a nonplanar metastable configuration with stacking faults in adjacent prismatic planes joined by a two-layer pyramidal twin.Plastic deformation in metals results mainly from the motion of line defects called dislocations. Many dislocation properties derive from the atomic-scale structure of their core, the region in the immediate vicinity of the dislocation line where crystallinity is disrupted. One such property is cross slip, i.e., the ability for screw dislocations to change glide plane, a stress-releaving process central to strain hardening and fatigue resistance [1,2].Thus far, cross slip has mostly been studied in facecentered cubic (fcc) metals for the conventional planar dissociated 1/2 110 {111} dislocations. Elasticity models [2,3] confirmed by atomic-scale simulations [4,5] showed that the dominant cross-slip mechanism involves a local constriction of the dislocation in its initial glide plane followed by redissociation in the crossslip plane (Friedel-Escaig mechanism). Another mechanism, which occurs under higher stresses met, for instance, in nanocrystalline plasticity [6], involves the successive change of glide plane of both partial dislocations [7]. Mechanisms involving a metastable configuration of the screw dislocation spread over several planes are also possible, as found in iridium [8].Cross slip is also observed in hexagonal close-packed (hcp) metals. In zirconium and titanium, 1/3 1210 dislocations are dissociated and glissile in prismatic {1010} planes [9], as confirmed by first-principles calculations [10,11]. But screw dislocations have also been reported experimentally to glide at high temperatures in both first-order pyramidal π 1 {1011} planes [12][13][14] and basal {0001} planes [12, 15] (see Fig. 1 for a graphical description of these planes). These secondary-slip processes do not correspond to cross slip as understood in fcc metals because the parent and the cross-slipped glide planes are not equivalent. Rather, this secondary slip in hcp metals is related to the fundamental question: how can a dislocation dissociated in a plane glide in another plane?In this Letter, we employ a combination of firstprinciples and empirical potential atomic-scale calculations to study secondary slip in hcp metals. We focus mainly on zirconium, although we checked that the present findings also apply to titanium. We show that unexpectedly, both basal and pyramidal slips are limited by the same thermally activated process, which involves an unusual motion of the prismatic stacking fault perpendicularly to itself, and results in a no...

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“…We also performed atomistic simulations with the embedded atom method (EAM) potential developed by Mendelev and Ackland [22] to check the validity of our results in larger simulation cells. This potential is suitable to model screw dislocations, predicting, in particular, dissociation in a prismatic plane [23], in contrast with most other empirical potentials.…”

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confidence: 99%

First-Principles Study of Secondary Slip in Zirconium

2014

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“…iron_carbon -complete asymmetric potential set for Fe-C simulations [12,20] zirconium -single species Zr hcp potential [21] pairpot -multispecies Lennard-Jones potential with parameters read at runtime morse -multispecies Morse potential with parameters read at runtime generic_atvf -generic potential loading module to load cubic spline potential coefficients from disk at runtime [22] The generic potentials currently offer single species potentials for Al, Cs, K, Li, Mo, Na, Nb, Rb, Ta, V, W, Cu, Au, Ag, Ni, Ti, Zr, and Pt. In addition, Ni-Al cross species potentials are included.…”

Section: Available Potentialsmentioning

confidence: 99%

The MOLDY short-range molecular dynamics package

Ackland

D'Mellow

Daraszewicz

et al. 2011

Computer Physics Communications

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We describe a parallelised version of the MOLDY molecular dynamics program. This Fortran code is aimed at systems which may be described by shortrange potentials and specifically those which may be addressed with the embedded atom method. This includes a wide range of transition metals and alloys. MOLDY provides a range of options in terms of the molecular dynamics ensemble used and the boundary conditions which may be applied. A number of standard potentials are provided, and the modular structure of the code allows new potentials to be added easily. The code is parallelised using OpenMP and can therefore be run on shared memory systems, including modern multicore processors. Particular attention is paid to the updates required in the main force loop, where synchronisation is often required in OpenMP implementations of molecular dynamics. We examine the performance of the parallel code in detail and give some examples of applications to realistic problems, including the dynamic compression of copper and carbon migration in an iron-carbon alloy. Moldy addresses the problem of many atoms (of order 10 6 ) interacting via a classical interatomic potential on a timescale of microseconds. It is designed for problems where statistics must be gathered over a number of equivalent runs, such as measuring thermodynamic properities, diffusion, radiation damage, fracture, twinning deformation, nucleation and growth of phase transitions, sputtering etc. In the vast majority of materials, the interactions are non-pairwise, and the code must be able to deal with many-body forces. Solution method: Molecular dynamics involves integrating Newton's equations of motion. MOLDY uses verlet (for good energy conservation) or predictor-corrector (for accurate trajectories) algorithms. It is parallelised using open MP. It also includes a static minimisation routine to find the lowest energy structure. Boundary conditions for surfaces, clusters, grain boundaries, thermostat (Nose), barostat (ParrinelloRahman), and externally applied strain are provided. The initial configuration can be either a repeated unit cell or have all atoms given explictly. Initial velocities are generated internally, but it is also possible to specify the velocity of a particular atom. A wide range of interatomic force models are implemented, including embedded atom, morse or Lennard Jones. Thus the program is especially well suited to calculations of metals. KeywordsRestrictions: The code is designed for short-ranged potentials, and there is no Ewald sum. Thus for long range interactions where all particles interact with all others, the order-N scaling will fail. Different interatomic potential forms require recompilation of the code. Additional comments: There is a set of associated open-source analysis software for postprocessing and visualisation. This includes local crystal structure recognition and identification of topological defects. Running time: A set of test modules for running time are provided. The code scales as order N. The parallelisation ...

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“…were performed using two different interatomic potentials, namely A95 and the potential described in [13], which we denote as M07. In these cases, strain was applied at a constant rate of 25x10 6 s -1 by applying a constant velocity to the upper rigid block of atoms.…”

Section: Modelmentioning

confidence: 99%

Interaction of a moving { } twin boundary with perfect dislocations and loops in a hcp metal

Serra

Bacon

2010

Philosophical Magazine

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. Interaction of a moving 101-2 twin boundary with perfect dislocations and loops in an HCP metal. Philosophical Magazine, Taylor & Francis, 2010, 90 (07-08) AbstractAtomic-scale computer simulation is used to investigate the interaction of a moving twin boundary in an HCP metal with either a straight 1/3 dislocation lying perpendicular to the direction of twinning shear or a periodic row of perfect dislocation loops. The screw dislocation does not decompose in the moving interface and has no effect on its motion. The 60° mixed dislocation is attracted by the boundary and decomposes into twinning dislocations and a disconnection (an interfacial defect with both step and dislocation character): the sign of the crystal dislocation determines the form of the disconnection and thus its effect on twin boundary motion.Boundary reactions with crystal dislocations are likely to be important for assisting the twinning process. Loops with Burgers vector, b, parallel to the interface are reformed in the other crystal after the twin boundary has passed through. The boundary attracts both interstitial and vacancy dislocation loops with inclined b but is not transparent to them, for the complete loop is swept along its glide prism by the moving interface.Depending on its nature, a loop either retains its structure in its parent crystal or is absorbed in the interface. The decomposition product in the latter case is consistent with the reactions of straight dislocations. The results indicate that twinning is efficient at sweeping loops from the microstructure when their density is low and is suppressed by loops when their density is high.

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Development of an interatomic potential for the simulation of phase transformations in zirconium

Cited by 312 publications

References 23 publications

First-Principles Study of Secondary Slip in Zirconium

First-Principles Study of Secondary Slip in Zirconium

The MOLDY short-range molecular dynamics package

Interaction of a moving { } twin boundary with perfect dislocations and loops in a hcp metal

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