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1224-GG05-15

MD Simulation of Dislocation Dynamics in Copper Nanoparticles Yoshiaki Kogure, Toshio Kosugi, Tadatoshi Nozaki and Masao Doyama Teikyo University of Science and Technology, 2525 Yatsusawa, Uenohara, Yamanashi 4090193, Japan ABSTRACT Atomistic configuration and motion of dislocation have been simulated by means of molecular dynamics method. The embedded atom method potential for copper is adopted in the simulation. Model crystal is a rectangular solid containing about 140,000 atoms. An edge dislocation is introduced along [112] direction near the center of model crystal, and the system is relaxed. After the dislocation configuration is stabilized, a shear stress is applied and released. Wavy motion of dislocation is developed on the Peierls valleys when the free boundary condition is adopted. Motion of pinned dislocation is also simulated. INTRODUCTION The mechanical relaxation due to dislocation has been observed in copper, aluminum and other metals by means of internal friction measurements. Broad relaxation peaks observed at temperatures between 100 K and 200 K in the deformed samples are called Bordoni peak. If these relaxation peaks are analyzed based on the double kink formation mechanism, a larger value of Peierls stress, 10−3 µ , is derived, where µ is the shear modulus [1]. One of the present authors Kosugi discovered a new relaxation peak at 11 K in zone-refined aluminum samples, and derived Peierls stress was in the order of 10−5 µ , which is reasonable size as expected from the plastic deformation experiments [2]. On the other hand, we have performed a MD simulation of dislocation motion in 2-d model. In the simulation, the total kinetic energy is found to make a bump in the time variation, when the dislocation surmount a Peierls potential hill. Estimated Peierls stress is in the order of 10−5 µ from the size of the hump [3]. The purpose of the present study is to develop a 3-d model for the simulation of dislocation in copper, and to investigate the structure and the motion of dislocations. A newly developed embedded atom method potential [4] is used in the present simulation. The potential function has successfully been applied on the simulation of the dynamics of crystal defects and nanoparticles [5-8]. Many studies of dislocations by MD simulation have been performed under the periodic boundary condition. To determine the Peierls stress a dislocation dipole of a straight line is introduced in a periodic super cell in the simulations to compensate the long range strain [9]. The fixed or the free boundary condition is adopted in the present simulation to realize the flexible dislocation appeared in the internal friction experiments. METHOD OF SIMULATION Molecular dynamics simulation has been performed by using an EAM potentials. The potential energy for the i-th atom is expressed as

Ei = F ( ρi ) + ∑ φ (rij ) / 2 ,

(1)

j

where F ( ρi ) is the embedding energy for the i-th atom and ρi is the electron density function, which is a sum of electron density of neighbor atoms labeled by j .