Characterization and visualization of the lattice misfit associated with dislocation cores

Hartley, Craig S.; Mishin, Y.

doi:10.1016/j.actamat.2004.11.027

Cited by 150 publications

(103 citation statements)

References 11 publications

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“…1 shows the c + a edge and screw dislocation core structures on pyramidal II planes as predicted by the MEAM potential 26 and DFT 45 . Dislocation core structures are visualized using both the component of the Nye tensor plot 46 and differential displacement plot 47 . The MEAM potential and DFT calculation predict similar core structures; both the edge and screw dislocations dissociate into partials of 1/2 c + a on Pyr.…”

Section: Meam Potentialmentioning

confidence: 99%

The origins of high hardening and low ductility in magnesium

Curtin

2015

Nature

570

170

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Magnesium is the ultimate lightweight structural metal but exhibits low ductility connected to unusual, mechanistically-unexplained, dislocation/plasticity phenomena, which make it difficult to form and use in energy-saving lightweight structures. Here, long-time molecular dynamics simulations using a DFT-validated interatomic potential reveal the fundamental origins of the previouslyunexplained phenomena and show a clear path toward design of new ductile magnesium alloys. The key c + a dislocation is metastable on easy-glide pyramidal II planes and undergoes a thermallyactivated, stress-dependent transition to one of three lower-energy, basal-dissociated immobile dislocation structures, which (i) cannot contribute to plastic straining and (ii) serve as strong obstacles to the motion of all other dislocations. The transition is intrinsic to magnesium, driven by reduction in dislocation energy and predicted to occur at very high frequency at room temperature, thus eliminating all major dislocation slip systems able to contribute to c-axis strain and leading to its low ductility.Enhancing ductility can thus be achieved by delaying, in time and temperature, the transition from the easy-glide metastable dislocation to the immobile basal-dissociated structures, and our results provide the underlying insights needed to guide the design of ductile magnesium alloys. * Corresponding author: william.curtin@epfl.ch 1 This is a post-print of the following article: Wu, Z. & Curtin, W. A. The origins of high hardening and low ductility in magnesium. Nature 526, 62-67 (2015). The final publication is available at http://dx.doi.org/10.1038/nature15364Developing lightweight structural metal is a crucial step on the path toward reduced energy consumption in many industries, especially automotive 1,2 and aerospace 3 . Magnesium (Mg) is the ultimate lightweight metal, with a density 23% that of steel and 66% that of aluminum, and so has tremendous potential to achieve energy efficiency 4 . In spite of this tantalizing property, Mg generally exhibits low ductility, insufficient for the forming and performance of structural components. The low ductility is associated with the inability of hexagonally-close-packed (hcp) Mg to deform plastically in the crystallographic c direction, which is accomplished primarily by dislocation glide on the pyramidal II plane with the c + a Burgers vector 5 (see Fig. 1).Experiments reveal a range of unusual, confounding, conflicting, and mechanistically-unexplained phenomena connected to c+a dislocations that coincide with the inability of Mg to achieve high plastic strains 6 . Uncovering and controlling the fundamental behavior of c + a dislocations is thus the key issue in Mg, and any solution would catapult Mg science, technology, and applications forward. Success would enable, for instance, lightweight automobiles that would consume less energy, independent of the energy source, and thus act as a multiplier for many other energyreduction strategies.Due to its critical importance and pro...

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Section: Meam Potentialmentioning

confidence: 99%

The origins of high hardening and low ductility in magnesium

Curtin

2015

Nature

570

170

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“…The resulting system is periodic along the dislocation line direction (z, also parallel to the Burgers vector). The dislocation core was tracked using the Nye tensor analysis [35]. Replication of the system along the line direction z allows carrying out averages of Nye tensor components during a molecular dynamics simulation at high temperature.…”

Section: Screw Dislocationmentioning

confidence: 99%

Modelling defects in Ni–Al with EAM and DFT calculations

Bianchini

Kermode

Vita

2016

Modelling Simul. Mater. Sci. Eng.

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We present detailed comparisons between the results of embedded atom model (EAM) and density functional theory (DFT) calculations on defected Ni alloy systems. We find that the EAM interatomic potentials reproduce low-temperature structural properties in both the γ and γ′ phases, and yield accurate atomic forces in bulk-like configurations even at temperatures as high as ∼1200 K. However, they fail to describe more complex chemical bonding, in configurations including defects such as vacancies or dislocations, for which we observe significant deviations between the EAM and DFT forces, suggesting that derived properties such as (free) energy barriers to vacancy migration and dislocation glide may also be inaccurate. Testing against full DFT calculations further reveals that these deviations have a local character, and are typically severe only up to the first or second neighbours of the defect. This suggests that a QM/MM approach can be used to accurately reproduce QM observables, fully exploiting the EAM potential efficiency in the MM zone. This approach could be easily extended to ternary systems for which developing a reliable and fully transferable EAM parameterisation would be extremely challenging e.g. Ni alloy model systems with a W or Re-containing QM zone.

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“…[22] For our purpose, a modified version of the bond-angle analysis [23] with the capability to identify crystalline structures and complex stacking defects inherent to Ni 3 Al was implemented. Furthermore, this tool combines Nye-tensor analysis for Burgers vector identification [24,25] and dislocation skeletonization. [26] For complementary analysis, the centrosymmetry parameter (CSP) as well as the coordination number for binary systems were used.…”

Section: Methodsmentioning

confidence: 99%

Atomistic Simulations of Compression Tests on Ni₃Al Nanocubes

Amodeo

Begau

Bitzek

2014

Materials Research Letters

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Supplementary Material Available OnlineThe deformation behaviour of nano-sized Ni 3 Al cubes with {100} side surfaces is investigated under uniaxial compression using constant-temperature molecular dynamics simulations at 300 K. The simulations reproduce key features of recently performed nanocompression experiments, namely the lack of strain hardening, homogeneous deformation of the entire sample and overall high stress levels of the order of 3-5 GPa. According to the simulations, the critical initial step is the formation of a pseudo-twin structure, which then further deforms by Shockley partial dislocations. These deformation mechanisms differ significantly from bulk Ni 3 Al and are rationalized in terms of generalized stacking fault energies and resolved shear stresses.

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Characterization and visualization of the lattice misfit associated with dislocation cores

Cited by 150 publications

References 11 publications

The origins of high hardening and low ductility in magnesium

The origins of high hardening and low ductility in magnesium

Modelling defects in Ni–Al with EAM and DFT calculations

Atomistic Simulations of Compression Tests on Ni₃Al Nanocubes

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Characterization and visualization of the lattice misfit associated with dislocation cores

Cited by 150 publications

References 11 publications

The origins of high hardening and low ductility in magnesium

The origins of high hardening and low ductility in magnesium

Modelling defects in Ni–Al with EAM and DFT calculations

Atomistic Simulations of Compression Tests on Ni3Al Nanocubes

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Product

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Atomistic Simulations of Compression Tests on Ni₃Al Nanocubes