Cross Slip in Cu - A Molecular Dynamics Study
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Cross Slip in Cu - A Molecular Dynamics Study Dan Mordehai1, Guy Makov2 and Itzhak Kelson1 School of Physics and Astronomy, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel. 2 Department of Physics, NRCN, PO.Box 9001, Be'er Sheva, Israel 1
ABSTRACT The annihilations of screw dislocation dipoles via cross-slip in Cu were simulated using constant-temperature constant-stress molecular dynamics. The cross-slip mechanism and annihilation process of flexible dislocations in a large dipole configuration was identified as a dynamic variant of the Friedel-Escaig mechanism. The cross-slip rate was found to exhibit exponential dependence on the temperature, from which the activation enthalpy for the cross-slip process was calculated by the Arrhenius relation. INTRODUCTION It has been known for many years that dislocations play a significant role in material response behavior. However, little is known about the quantitative relations between dislocation properties and macroscopic material behavior. Accordingly, one of the key problems in quantitative analysis of material properties is the description of the dynamics of dislocations and their interaction ([1]). For example, in order to fully understand stage III plasticity in fcc metals, a detailed model for dislocation cross-slip should be introduced. One of the main tools to study dislocation properties in detail are atomistic calculations. Several works describing atomistic simulations of cross-slip in Cu were published in recent years [2-5]. One of the most comprehensive works describes cross-slip of screw dislocations using the nudged elastic band technique (NEB) is [2]. In this method the system is simulated along the minimal energy path rather than by calculating the full time dependent dynamics. The authors showed that the simulated path for cross-slip and annihilation fits the Friedel-Escaig mechanism. A few molecular dynamics (MD) calculations were made in order to calculate the activation energy and rate for spontaneous annihilation of close screw dislocations in a dipole structure [6]. In an earlier work by Duesbery, a two dimensional model was used to describe cross-slip at T=0K ([3]). In this work, he calculated the stress required on the cross-slip plane in Cu to initiate cross-slip. He found this stress to be above 0.023µ. In these simulations it was shown that in order to cross-slip the dislocation does not need to fully constrict. Recently a very detailed review of cross-slip models and calculations was presented by Püschl ([4]). In the present work, we study the cross-slip mechanism in Cu and the annihilation of screw dislocation dipoles using a 3 dimensional constant-stress constant-temperature MD. This method enables us to initiate cross-slip within reasonable calculation times, and to study the cross-slip mechanism. Repeating the calculations under various thermodynamic conditions (temperature and external stress), the activation enthalpy was calculated.
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