Materials Science and Engineering A 400–401 (2005) 325–328 Dislocation reactions and junctions in MgO Philippe Carrez a,∗ , Patrick Cordier a , Benoit Devincre b , Ladislas P. Kubin b a Laboratoire de Structure et Propri´ et´ es de l’Etat Solide, UMR CNRS 8008, Universit´ e de Lille 1, 59655 Villeneuve d’Ascq Cedex, France b Laboratoire d’Etude des Microstructures, CNRS-ONERA, 29 Avenue de la Division Leclerc, BP 72, 92322 Chˆ atillon Cedex, France Received 13 September 2004; received in revised form 20 December 2004; accepted 28 March 2005 Abstract Deformation processes in MgO single crystals are simulated at the mesoscopic scale using 3-D dislocation dynamics simulations. Our goal is to understand the strong hardening properties of this material through interactions and reactions between dislocations gliding in non-coplanar slip systems. This study focuses on interactions between dislocations of the 1/2〈110〉{110} slip systems. The systematic modeling of dislocation intersections shows that only sessile “Lomer-like” junctions are energetically favorable which is consistent with previous observations. © 2005 Elsevier B.V. All rights reserved. Keywords: MgO single crystal; Dislocation dynamics simulations; Dislocations junctions 1. Introduction Magnesium oxide is one of the model ceramics that has been largely studied in the past mainly due to its potential as an important refractory material for energy production [1–4]. Alloyed to FeO, it is also likely to be the second most abundant phase of the lower mantle [5]. Thus, mechanical properties of this material are not only important in Materials Science, but also in Earth Sciences. MgO exhibits a strong hardening which is usually attributed to a high rate of dis- location storage [3,6]. To understand the effect of a possible dislocation “forest” hardening in MgO, a first approach consists in looking at dislocation reactions, which constitute obstacles to further dislocation motion. In the present study, dislocation interactions are studied using dislocation dynam- ics (DD) modeling. Indeed, dislocation dynamics simulations have already shown their efficiency for modeling mechanical properties of single crystals at the mesoscopic scale [7–10]. A DD simulation has been adapted to the case of MgO. Details of the code used are given in several previous studies [7,8] and will not be recalled here. In what follows, the influ- ence of orientation on the interactions between two straight ∗ Corresponding author. Tel.: +33 320 434861; fax: +33 320 436591. E-mail address: philippe.carrez@univ-lille1.fr (P. Carrez). dislocations gliding on different slip planes is systematically investigated. 2. Dislocations and slip systems in MgO MgO is an ionic crystal exhibiting a rock-salt structure similar to that of NaCl. The Bravais lattice of MgO is fcc, space group Fm ¯ 3m. Its lattice parameter is 0.4211 nm. In this structure, the Mg + and O 2- ions are displaced by half a diag- onal of the cube. The predominant slip systems in NaCl-type crystals are 1/2〈110〉{110}. Each {110} plane contains a single slip direction, which results in six possibilities: 1/2[1 1 0]( ¯ 1 1 0), 1/2[1 ¯ 1 0](1 1 0), 1/2[0 1 1](0 ¯ 1 1), 1/2[0 1 ¯ 1](0 1 1), 1/2[1 0 1]( ¯ 1 0 1), 1/2[1 0 ¯ 1](1 0 1) The active slip planes are either orthogonal or cut each other at π/3 (Fig. 1). Slip is also possible in other close-packed planes such as {100} or {111}. From single crystal defor- mation experiments at 0.63T m , Routbort [2] showed that slip in 1/2〈110〉{110} alone was about four times easier than combined slip on 1/2〈110〉{110} and 1/2〈110〉{001}. Re- cent analyses of orientations in (Mg, Fe)O polycrystals de- formed in torsion suggest that {111} glide is involved at 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.03.071