Molecular dynamics simulation of screw dislocation interaction with stacking fault tetrahedron in face-centered cubic Cu
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Jae-Hyeok Shim Nuclear Engineering Department, University of California, Berkeley, California 94720; and Materials Science and Technology Research Division, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
Brian D. Wirth Nuclear Engineering Department, University of California, Berkeley, California 94720 (Received 25 January 2007; accepted 22 May 2007)
The interaction of a gliding screw dislocation with stacking fault tetrahedron (SFT) in face-centered cubic (fcc) copper (Cu) was studied using molecular dynamics simulations. Upon intersection, the screw dislocation spontaneously cross slips on the SFT face. One of the cross-slipped Shockley partials glides toward the SFT base, partially absorbing the SFT. At low applied stress, partial absorption produces a superjog, with detachment of the trailing Shockley partial via an Orowan process. This leaves a small perfect SFT and a truncated base behind, which subsequently form a sheared SFT with a pair of opposite sense ledges. At higher applied shear stress, the ledges can self-heal by gliding toward an SFT apex and transform the sheared SFT into a perfect SFT. However, complete absorption or collapse of an SFT (or sheared SFT) by a moving screw dislocation is not observed. These observations provide insights into defect-free channel formation in deformed irradiated Cu.
I. INTRODUCTION
Many experimental results report the change in mechanical behavior following high-energy particle irradiation of metallic materials.1–6 For irradiation at low-tointermediate temperature (T 艋 0.5Tm), the characteristic changes include an increase in yield stress and a decrease in ductility. The yield stress increase is attributed to the production of a high number of radiation induced defects, which may include cavities, interstitial dislocation loops, and stacking fault tetrahedra (SFT), etc., depending on material and irradiation condition. These defect clusters act as obstacles to dislocation motion, thus changing the local deformation behavior of the materials, observed as an increase in the yield stress. The underlying cause of the ductility decrease in irradiated materials is an active subject of ongoing research. Transmission electron microscopy (TEM) observations of irradiated materials prior to and following deformation reveal the formation of defect free channels, which appear as a cleared band with a very low visible defect a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0345 2758 J. Mater. Res., Vol. 22, No. 10, Oct 2007 http://journals.cambridge.org Downloaded: 09 Jul 2014
cluster density.5 Early models proposed that a single dislocation interaction with a radiation induced defect cluster led to sweeping or annihilation, producing decreased resistance for subsequent dislocation glide in a localized region of the material.7 Currently, the defect removal mechanisms are believed to be more complex and include (i) multiple shearing of the defects to an invisible small size, (ii) transformation o
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