Monte Carlo Simulations of Grain Boundary Sliding and Migration: Effect of Temperature and Vacancy
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Monte Carlo Simulations of Grain Boundary Sliding and Migration: Effect of Temperature and Vacancy P.Ballo1, N.Kioussis2 and Gang Lu2 1 Department of Physics, Faculty of Electrical Engineering and Information Technology Slovak University of Technology, Ilkoviþova 3,812 19 Bratislava, Slovak Republic 2 Department of Physics and Astronomy, California State University, Northridge, CA 91330-8268, U.S.A. ABSTRACT We have carried out Monte Carlo (MC) simulations using the embedded atom potential to study the sliding and migration of the Σ5 [001] (210) tilt grain boundary (GB) in aluminum and the effect of vacancies on the sliding properties. We find that the simulated annealing allows the system to gradually anneal to a global-minimum configuration, thus increasing the number of migrations and reducing the GB sliding energy barriers to about a factor of three compared to the corresponding "static’’ values. The distribution of atomic energies as a function of GB displacement, provide insight into which atoms are responsible for the GB migration. The vacancy formation energy is found to be lower when the vacancy is placed on the first layer to the boundary, in excellent agreement with ab initio electronic structure calculations. The sliding and migration properties depend very sensitively on the position of the vacancy in the GB core. INTRODUCTION Grain boundary sliding (GBS), i.e., the rigid translation of one grain over another parallel to the boundary interface, is one of the principal mechanisms of plastic flow of polycrystalline materials at intermediate-to-high temperatures (above 0.4TM, where TM is the melting point) [1]. Another process that may occur during the GBS is grain boundary migration, which is the motion of the interface in the direction perpendicular to the boundary plane [2]. Finally, the interaction between a grain boundary and other defects in the crystal, such as substitutional impurities, vacancies and dislocations will affect the grain boundary motion [3]. Despite the important role of GB in materials properties, our knowledge at the microscopic level is limited. The direct observation is limited due to lack of resolution of experimental techniques such as high resolution transmission electron microscopy (HRTEM) and by the fact that only a full relaxed structure can be observed. With the advent of highly powerful computers, simulations at atomic level can play an increasingly prominent role as an effective alternative to experimental observation. Computer simulation offers the ability to examine the details at microscopic scale that cannot be obtained from experiment. For example, some simulations have been done by Bishop et al. [4] using pair-like potential. Recently Chandra et al.[5] using an Embedding atom method potential and Molteni et al. [6] using an ab initio simulation of GBS received evidence of interface migration. However, the vast majority of computer simulation studies of GB have been concerned with the equilibrium structure at zero temperature. The results obtained with these simulati
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