Dislocation Intersections and Reactions in FCC and BCC Crystals
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Dislocation Intersections and Reactions in FCC and BCC Crystals Ladislas P. Kubin, Ronan Madec1 and Benoit Devincre Laboratoire d'Etude des microstructures, CNRS-ONERA, 29 Av. de la Division Leclerc, BP 72, 92322 Chatillon Cedex, France 1 Now at: DPTA, Commissariat à l'Energie Atomique, BP12, 91680 Bruyères-le-Châtel, France ABSTRACT The various types of configurations formed in face-centered cubic (fcc) and body-centered cubic (bcc) structures by two interacting, non-coplanar, dislocation segments of various orientations are examined and discussed. The focus is on junction formation and on a particular interaction, the collinear interaction, which deserves much more attention than paid up to now.
INTRODUCTION As first stated by Taylor [1], strain hardening in crystals stems from dislocation interactions. Within the widely accepted "forest model" [2, 3], the formation and the destruction of junctions or locks produced by attractive interactions between non-coplanar dislocations contribute to most of the flow stress in conditions of multiple slip. The stability of junctions is governed by selfenergies, which are mainly elastic in nature since the contribution of the dislocation cores is comparatively negligible. This allowed performing studies on particular junction configurations in several simple crystal structures, fcc [4, 5], see also [6], bcc [7, 8] and hexagonal close-packed [9]. More recent studies of individual junction configurations at the atomic scale [10, 11] and at the mesoscopic scale [12-15] have confirmed the validity of such elastic approaches. At the mesoscale, however, analytical elastic calculations cannot fully account for the mutual distortions of interacting dislocations lines. This is why dislocation dynamics (DD) simulations are particularly suited for a more precise treatment of such problems. The aim of the present study is to provide a global insight into the interactions and reactions of two dislocation segments in fcc and bcc crystals, stressing their dependence on the initial orientation of the lines. Some aspects of the simulation technique used in the present study are summarized. Mappings of dislocation reactions are then presented and discussed, with emphasis on an intersection process which has been largely ignored up to now and has recently be found to be of prominent importance, the collinear interaction. Concluding remarks are finally presented.
METHODOLOGY Use is made of a DD simulation, in which segments with a finite set of orientations are embedded into an elastic medium and move by discrete translations in an underlying mesoscopic lattice with same symmetry elements as the considered crystal. An early version of this simulation, in which continuous dislocation shapes were discretized into edge and screw segments, has been described is some detail [16, 17]. The updated version used in the present work is based on the same principles, which are discussed in [15, 18], but makes use of an
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