Atomistic Simulation of Dislocation-Defect Interactions in Cu
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Atomistic Simulation of Dislocation-Defect Interactions in Cu B. D. Wirtha, V. V. Bulatov and T. Diaz de la Rubia, Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550 ABSTRACT The mechanisms of dislocation-defect interactions are of practical importance for developing quantitative structure-property relationships, mechanistic understanding of plastic flow localization and predictive models of mechanical behavior in metals under irradiation. In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. Thus, the resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present a comprehensive molecular dynamics simulation study that characterizes the interaction and fate of moving dislocations with stacking fault tetrahedra in Cu using an EAM interatomic potential. This work is intended to produce atomistic input into dislocation dynamics simulations of plastic flow localization in irradiated materials. INTRODUCTION It is well established that irradiation of metals by high-energy neutrons and ions produces significant changes in material microstructure and mechanical properties [1-5]. In low stacking fault energy face centered cubic (fcc) metals, stacking fault tetrahedra (SFT) are the primary defect observed following high-energy particle irradiation. For example, post-irradiation microstructural examination of copper irradiated at temperatures between 20 and 100 °C and doses between 10-4 and 102 dpa reveals that approximately 90% of the high number density (about 1023 m-3) of radiation-induced defects are SFTs and that the average SFT size remains constant at about 2.5 ± 0.5 nm [3,6]. When deformed after irradiation, Cu and other low stacking fault energy fcc metals exhibit significant mechanical property degradation, including a sharp increase in yield stress, a decrease in ductility and often, plastic flow localization in the form of defect-free dislocation channels [2,5]. The formation of dislocation channels is commonly attributed to dislocation absorption of the vacancies contained in SFTs [7]. However, a concise atomistic picture of the SFT absorption mechanism is lacking. Thus, the objective of this work is to obtain atomistic insight into the interaction of SFTs with dislocations, necessary to understand radiation-induced mechanical property changes. Computer simulation studies have been used to successfully model the production and accumulation of damage in irradiated Cu [8-13] and some key results of our work are briefly summarized here. Molecular dynamics (MD) simulations of displacement cascade evolution in Cu reveal the formation of large vacancy and self-interstitial
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