Basal and prism dislocation cores in magnesium: comparison of first-principles and embedded-atom-potential methods predictions

Abstract

The core structures of screw and edge dislocations on the basal and prism planes in Mg, and the associated gamma surfaces, were studied using an ab initio method and the embedded-atom-method interatomic potentials developed by Sun et al and Liu et al. The ab initio calculations predict that the basal plane dislocations dissociate into partials split by 16.7 Å (edge) and 6.3 Å (screw), as compared with 14.3 Å and 12.7 Å (Sun and Liu edge), and 6.3 Å and 1.4 Å (Sun and Liu screw), with the Liu screw dislocation being metastable. In the prism plane, the screw and edge cores are compact and the edge core structures are all similar, while ab initio does not predict a stable prismatic screw in stress-free conditions. These results are qualitatively understood through an examination of the gamma surfaces for interplanar sliding on the basal and prism planes. The Peierls stresses at T = 0 K for basal slip are a few megapascals for the Sun potential, in agreement with experiments, but are ten times larger for the Liu potential. The Peierls stresses for prism slip are 10–40 MPa for both potentials. Overall, the dislocation core structures from ab initio are well represented by the Sun potential in all cases while the Liu potential shows some notable differences. These results suggest that the Sun potential is preferable for studying other dislocations in Mg, particularly the ⟨c + a⟩ dislocations, for which the core structures are much larger and not accessible by ab initio methods.

Magnesium interatomic potential for simulating plasticity and fracture phenomena

“…Comparing the GSF energy surfaces shows that the basal plane has the lowest stacking fault energy along the dislocation slip direction, followed by the prismatic plane. The minimum energy path (MEP) on the prismatic plane is along the a direction, consistent with DFT calculations [14] and in contrast with previous study [13,14] using EAM potentials (Liu [11] and Sun [12]) where unusual MEPs on prismatic plane were found. On the pyramidal I and II planes, the stacking fault energies along the c + a dislocation slip direction are similar, and substantially higher than those on basal and prismatic planes.…”

“…The Version of Record is available online at http://dx.doi.org/10.1088/0965-0393/23/1/015004. [42] f Reference [43] g Reference [13] h Reference [44] difficult than nucleation of a dislocations on basal and prismatic planes. The MEP on the pyramidal II plane follows the c + a direction while on the pyramidal I plane, the MEP is more complex.…”

Deformation of periodic nanovoid structures in Mg single crystals

“…plane are 13 and 9.3 MPa using the EAM [30] and MEAM potentials [29], respectively, in contrast to our simulations results that the former leads to a lower yield stress than the latter. This indicates that other quantities, such as the critical stress required to nucleate the dislocation from the void surface, need to be taken into account to justify the potential-dependent difference.…”

“…In other words, the MEAM-based predictions are closer to the Lubarda model with ρ = 1, while the EAM-based ones are closer to that with ρ = 2. On the other hand, previous studies [30,36] found that the two interatomic potentials predict very similar core structures of dislocations on the prismatic plane, i.e., ρ ≈ 1.5. Thus, the difference in their yield stress must be attributed to factors other than the dislocation width, suggesting that the Lubarda model with only one adjustable parameter is oversimplified.…”

“…In all dynamic simulations, the time step is 2 fs. Two interatomic potentials -the embedded atom method (EAM) potential by Sun et al [28] and the modified embedded atom method (MEAM) potential by Wu et al [29], which are considered the most accurate in terms of the dislocation core description among all EAM and MEAM potentials for Mg, respectively [30,29] -are adopted for interactions between Mg atoms. The lattice constant a and the c/a ratio are 3.184 and 1.628 using the EAM potential, while 3.187 and 1.623 using the MEAM potential.…”