Atomic simulations of GB sliding in pure and segregated bicrystals
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Atomic simulations of GB sliding in pure and segregated bicrystals Motohiro Yuasa1, Yasumasa Chino1 and Mamoru Mabuchi2 1 National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, 463-8560 Japan 2 Kyoto University, Kyoto, 606-8501 Japan ABSTRACT Grain boundary (GB) sliding is an important deformation mode in polycrystals, and it has been extensively investigated, for example, there are many studies on influences of the atomic geometry in the GB region. However, it is important to investigate GB sliding from the electronic structure of GB for deeper understandings of the sliding mechanisms. In the present work, we investigated the GBs sliding in pure and segregated bicrystals with classical molecular dynamics (MD) simulations and first-principles calculations. It is accepted that the sliding rate is affected by the GB energy. However, there was no correlation between the sliding rate and the GB energy in either the pure or the segregated bicrystals. First-principles calculations revealed that the sliding rate calculated by the MD simulations increases with decreasing minimum charge density at the bond critical point in the GB. This held in both the pure and segregated bicrystals. It seems that the sliding rate depends on atomic movement at the minimum charge density sites. INTRODUCTION GB sliding is an important deformation mode in polycrystals, and it has been extensively investigated [1-4]. It has been found that the unique deformation behavior of the inverse HallPetch relation in nanocrystalline metals can be attributed to GB sliding [5]. Atomic shuffling plays an important role in GB sliding [4]. Because this shuffling is enhanced by defects at GBs, GB structures strongly affect the sliding behavior [6]. As a result, GB sliding depends on the misorientation [1] or the free volume [7]. Thus, there are significant understandings on influences of the atomic geometry on GB sliding. GB segregation is another interesting phenomenon, which could affect this process. There have been many experiments [8-10] and simulations [11-13] on effects of segregation on GB fracture. However, limited work as focused on the sliding of segregated GBs. Millett et al. [14] showed that oversized substitutional segregated atoms effectively retard GB sliding, while undersized substitutional segregated atoms enhance the sliding. However, Du et al. [15] suggested that the chemistry effect is more important than the size effect in the sliding behavior. Thus, natures of GB sliding are still in debate. The present work investigates the GB sliding of Σ9(221) bicrystals in a wide range of fcc metals including pure metals (Al, Ag, Au, Cu, Pt and Co) and segregated metals (Cu segregated by Al, Ag, Au, Pt and Co). The defect structures at the Σ9(221) GB often have the E structures [6]. In the present work, influences of the different elements and the segregated atoms on GB sliding are investigated assuming that the defect structures of all the bicrystals investigated consist of the E structures. The movement of a number of atom
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