Large-scale atomistic study of core structures and energetics of (()) dislocations in hexagonal close packed metals

Abstract

Using two different kinds of many-body potentials as well as the Lennard-Jones potential for hexagonal close packed metals, we have found that c + a edge dislocations with dislocation lines along 1 100 can split onto the basal plane, forming a non-planar sessile structure. The 'type I' undissociated dislocation core, observed in previous papers, is shown to be stable only for small simulations. The observed dissociated core structure has a large distorted region that we interpret as a (11 21) twin nucleus, which may help the formation of (11 21) tension twins. We also find that this core structure is lower in energy than the previously observed glissile 'type II' configuration, dissociated on the (11 22) plane. The sessile splitting of the core gives rise to non-Schmid behaviour, with the twin nucleus expanding under c-axis tension, and contracting under compression.

Analysis on Dissociation of Pyramidal I Dislocation in Magnesium by Generalized-Stacking-Fault Energy

“…(8) and (9), the slips on f30 34g and f30 32g planes are presented. Meanwhile, the 1=6h20 23i partial dislocation appears in both Eqs.…”

“…Meanwhile, the 1=6h20 23i partial dislocation appears in both Eqs. (8) and (9) due to the dissociation of the 1=3h 1 123i dislocation. This is consistent with our calculation of c surface shown in Fig.…”

“…In the research of hcp structures, it is widely recognized that the slip and twinning are the dominant deformation modes, especially, more attentions are focused on the hc ? ai slip in pyramidal I and II planes [1][2][3][4][5][6][7][8][9]. There are two focuses on the discussion of these two pyramidal hc ?…”

Atomistic study of edge and screw 〈c+a〉 dislocations in magnesium

“…Atomistic level modeling of dislocation structures and motion is one avenue through which insight into the deformation modes can be obtained. To this end, hc + ai dislocations have been studied at 0 K for several decades using simple interatomic potentials [1][2][3][4][5][6][7][8][9] and embedded atom method (EAM) potential [12,13], but the potentials were usually fitted to hcp zirconium or used very small computational cells of 9000 atoms with only 1000 atoms free to relax, which is too small to accurately capture the extended hc + ai dislocations. Only Liang and Bacon [7][8][9] used a pair potential designed for Mg, but that study was limited by the small cell size.…”

Locking of Dislocations without the Application of an External Stress: Experiment and Theory

“…В результате компьютерного моделирования [70][71][72] были полу-чены многочисленные формы ядра краевой (c  a)-дислокации, кото-рые включают релаксацию ядра, образование высокоэнергетическо-го поверхностного дефекта при расщеплении в плоскости пирамиды II, образование низкоэнергетического дефекта упаковки при рас-щеплении в плоскости базиса и т.д. В результате, если опустить де-тали, остаются следующие формы краевой (c  a)-дислокации: недис-социированная (стянутая) форма; ядро, диссоциированное (разма-занное) в исходной плоскости пирамиды II; ядро, диссоциированное (размазанное) в плоскости базиса и пересекающихся с ней плоско-стях.…”