Multiscale Modeling of Dislocation Processes in Bcc Tantalum: Bridging Atomistic and Mesoscale Simulations
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Multiscale Modeling of Dislocation Processes in Bcc Tantalum: Bridging Atomistic and Mesoscale Simulations L. H. Yang, Meijie Tang, and John A. Moriarty Physics and Advanced Technologies Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
ABSTRACT Plastic deformation in bcc metals at low temperatures and high-strain rates is controlled by the motion of a/2 screw dislocations, and understanding the fundamental atomistic processes of this motion is essential to develop predictive multiscale models of crystal plasticity. The multiscale modeling approach presented here for bcc Ta is based on information passing, where results of simulations at the atomic scale are used in simulations of plastic deformation at mesoscopic length scales via dislocation dynamics (DD). The relevant core properties of a/2 screw dislocations in Ta have been obtained using quantum-based interatomic potentials derived from model generalized pseudopotential theory and an ab-initio data base together with an accurate Green’s-function simulation method that implements flexible boundary conditions. In particular, the stress-dependent activation enthalpy for the lowest-energy kinkpair mechanism has been calculated and fitted to a revealing analytic form. This is the critical quantity determining dislocation mobility in the DD simulations, and the present activation enthalpy is found to be in good agreement with the previous empirical form used to explain the temperature dependence of the yield stress.
INTRODUCTION The low-temperature and high-strain-rate plastic deformation properties of bcc metals are controlled by a/2 screw-dislocation behavior in the crystalline lattice. In particular, the motion of the screw dislocation is believed to be associated with the formation and expansion of kink pairs on the screw dislocation line. Thus, the accurate prediction of kink-pair activation energetics is essential to the understanding and determination of the mobility of screw dislocations in these materials. In turn, an atomistic-based dislocation mobility model is a key ingredient needed to develop predictive multiscale simulations of crystal plasticity for bcc metals. At higher length scales, the dislocation dynamics (DD) simulation approach has shown some predictive power of the macroscopic plastic response of bcc single crystals based on the fundamental mechanisms of dislocation behavior [1]. However, the accuracy of DD simulations is limited in part by our understanding of the unit dislocation mechanisms and in part by the local rules that dominate the DD simulation process. Therefore, validating a realistic atomistic mobility model is an important first step in developing predictive DD simulations that intend to use atomistic data generated by the proposed kink-pair mechanism. The objectives of this study are twofold. First, it provides a critical link to allow data generated at the atomic length scale to be used directly in mesoscale DD simulations. Second, the DD simulation results can in turn
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