The Interaction of He with a ½<111>{110} Edge Dislocation in W and Mo

The positions of the metal atoms around a ½<111>{110} edge dislocation in Mo and W are calculated using the Wilson—Johnson potentials. The boundary conditions are given by anisotropic elasticity theory. The He—metal potential, also developed by Wilson and Johnson, is used to calculate the position with maximum energy gain for a He-atom

Disclinations, dislocations and continuous defects: a reappraisal

Disclinations, first observed in mesomorphic phases, are relevant to a number of ill-ordered condensed matter media, with continuous symmetries or frustrated order. They also appear in polycrystals at the edges of grain boundaries. They are of limited interest in solid single crystals, where, owing to their large elastic stresses, they mostly appear in close pairs of opposite signs. The relaxation mechanisms associated with a disclination in its creation, motion, change of shape, involve an interplay with continuous or quantized dislocations and/or continuous disclinations. These are attached to the disclinations or are akin to Nye's dislocation densities, well suited here. The notion of 'extended Volterra process' takes these relaxation processes into account and covers different situations where this interplay takes place. These concepts are illustrated by applications in amorphous solids, mesomorphic phases and frustrated media in their curved habit space. The powerful topological theory of line defects only considers defects stable against relaxation processes compatible with the structure considered. It can be seen as a simplified case of the approach considered here, well suited for media of high plasticity or/and complex structures. Topological stability cannot guarantee energetic stability and sometimes cannot distinguish finer details of structure of defects.Comment: 72 pages, 36 figure

DISLOCATION MOVEMENT IN DISTORTED CRYSTALS

On démontre que la méthode topologique communément utilisée pour définir le vecteur de Burgers d'une dislocation, peut conduire à violer la loi de conservation du vecteur de Burgers dans les cristaux distordus. La solution proposée ici est de considérer la stabilité d'une dislocation comme une propriété physique du réseau qui impose le module du vecteur de Burgers et son orientation par rapport au réseau. Si d'autre part le vecteur de Burgers est conservatif dans l'espace euclidien, la loi de conservation géométrique est rigoureusement assurée. Avec ce modèle, il est nécessaire de considérer tout changement de l'orientation ou du module du vecteur de Burgers comme causé par l'éclatement de dislocations partielles qui peuvent être stables ou pas. Les vecteurs de Burgers des dislocations instables laissées, dans chaque cellule unité, sur un plan de glissement incliné, par une dislocation stable, peuvent s'exprimer au moyen d'un changement de métrique et du vecteur de Darboux le long des trajectoires décrites par chaque point de la ligne de dislocation sur le plan de glissement incliné.It is demonstrated that the topological method of defining the Burgers vector of a dislocation, which is at present commonly used, may lead to violation of the « Burgers vector conservation law » in distorted crystals. The remedy proposed here is to consider the stability of a dislocation as a physical property of the lattice which prescribes the Burgers vector modulus and orientation relative to the lattice. On the other hand, if the Burgers vector is considered as conservative relative to Euclidean space, the geometrical conservation law is rigorously ensured. It is necessary in this model to regard any change in Burgers vector orientation or modulus as being caused by splitting off partial dislocations that may be stable or not. The Burgers vectors of the unstable dislocations left in each unit cell on a bent glide plane by a stable dislocation may be expressed in terms of the changing metric and Darboux vector along the trajectories described by each point of the dislocation line on the bent glide plane