Modeling the Effects of Dislocation-Grain Boundary Interactions in Polycrystal Plasticity: Identification and Characteri
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Modeling the Effects of Dislocation-Grain Boundary Interactions in Polycrystal Plasticity: Identification and Characterization of Unit Mechanisms M. de Koning1, R. Miller2, V.V. Bulatov1, F. Abraham3 1
Lawrence Livermore National Laboratory, University of California, CA 94550 University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5A9 Canada 3 IBM Research Division, Almaden Research Center, San Jose, CA 95120 2
ABSTRACT In this paper we focus on one of the key issues in polycrystalline plasticity: the unit mechanisms involving the interactions between dislocations and grain boundaries (GB). Using a combination of large-scale molecular dynamics simulations based on an embedded atom potential and an analysis in terms of the line-tension model we identify and characterize the geometrical parameters that govern the occurrence of slip transmission, absorption, blockage, etc. in dislocation-GB interactions. The results provide a guideline for the development of quantitative micro-constitutive equations for dislocation-GB interactions to be used in meso-scale simulations of polycrystal plasticity. INTRODUCTION Quantitative modeling of polycrystal plasticity requires an atomistic-micro-meso scale computational approach that couples the physics of individual dislocations to the evolution of large collections of dislocations and, ultimately, to the aggregate behavior of grain microstructures under stress. As a step in the construction of such a model one must understand the unit defect mechanisms that govern the behavior of the system at the atomistic level and provide the basis for a description on higher scales. One of the fundamental issues in this context concerns the elementary interactions between dislocations and grain boundaries. Characterization and quantification of such interactions is a very challenging task given the complex nature of the involved unit mechanisms. This complexity is reflected by a large set of possible parameters involved in such interactions: the Burgers vector and glide plane of the dislocation, the stress state on both sides of the grain boundary, five degrees of freedom describing the GB geometry [1] (lattice misorientation and boundary inclination) and possibly others. Specific combinations of these parameters may determine which combination of possible outcomes (blockage, transmission, absorption) actually occurs in a dislocation-GB collision event. Figure 1 gives an illustration of the complexity involved in characterizing and quantifying dislocation-GB interactions. It shows three atomistic configurations obtained from large-scale molecular dynamics (MD) simulations of dislocation-GB collisions in Ni modeled by an EAM potential [2]. In these simulations, dislocations were emitted from a crack tip in one of two grains separated by a symmetric tilt boundary. Under the influence of the crack tip stress, dislocation loops are nucleated on two planes oblique to the crack front. As the dislocations continue to expand under stress, their interaction with the boundary is seen to be quite diffe
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