Forces between Dislocations due to Dislocation Core Fields
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Forces between Dislocations due to Dislocation Core Fields Charles H. Henager, Jr.* and Richard G. Hoagland Pacific Northwest National Laboratory1 Richland, WA 99335-0999 ABSTRACT Atomistic dislocation models were used to determine the properties of dislocation core fields in Al using an EAM potential. Equilibrium atom configurations were compared with initial configurations displaced according to the Volterra field to determine core displacement fields for edge, screw, and mixed (60ÛDQGÛ JHRPHWULHV7KHFRUHILHOGZDVDSSUR[LPDWHGE\ a line force defect field lying parallel to the dislocation line direction. Best-fit parameters for the core fields were obtained in terms of the anisotropic elastic solution for a line force defect, from which the line force strengths and the origin of the line forces were determined. The line force stress fields were then used to compute the forces between dislocations for several dislocation configurations. The Volterra field dominates beyond 50b but core field forces modify the equilibrium angle of edge dislocation dipoles and determine the force between otherwise noninteracting edge and screw dislocations at distances out to 50b compared to the Volterra-only forces. INTRODUCTION Discrete dislocation simulations rely on knowledge of elastic forces between interacting dislocation segments moving on a discrete lattice network to track the evolution of dislocation position with time and applied stress [1]. The underlying discrete lattice has the symmetry properties of the crystal lattice but is much larger, the size being set by the minimum climb distance between two edge dislocations that can coexist on separate {111} planes without recombining spontaneously [1]. This distance is on the order of 10b, where b is the Burgers vector magnitude, and is an order of magnitude larger than assumed dislocation core radii in fcc metals. While the core radius is important in determining the range of accuracy of linear elasticity for discrete simulations, the presence of the core strain field has other consequences. The origin of the nonlinear dislocation core fields rests in third order elasticity and manifests itself as a volume change per unit length of dislocation line [2,3]. Most importantly, there are long range strain fields that can be attributed to nonlinear dislocation core fields [2,4-10]. This study examines the strength of these long-range fields using atomistic simulations carried out with an embedded atom method potential in aluminum [11]. Investigations of dislocation core fields using atomistic methods has provided details of core displacement fields that cannot be obtained using other approaches [2,8,12] and have demonstrated accurate representations of this field using line force defects [2,10,13]. We also pursue this approach in the present work. DETERMINATION OF LINE FORCE DEFECT PARAMETERS We used cylindrical atomistic models containing straight dislocations at the center of the model and having two regions; region I is an inner cylinder containing moveable atoms and
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