Atomistic Simulations of Dislocations in Confined Volumes
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P.M. Derlet, P. Gumbsch, R. Hoagland, J. Li, D.L. McDowell, H. Van Swygenhoven, and J. Wang Abstract Internal microstructural length scales play a fundamental role in the strength and ductility of a material. Grain boundaries in nanocrystalline structures and heterointerfaces in nanolaminates can restrict dislocation propagation and also act as a source for new dislocations, thereby affecting the detailed dynamics of dislocationmediated plasticity. Atomistic simulation has played an important and complementary role to experiment in elucidating the nature of the dislocation/interface interaction, demonstrating a diversity of atomic-scale processes covering dislocation nucleation, propagation, absorption, and transmission at interfaces. This article reviews some atomistic simulation work that has made progress in this field and discusses possible strategies in overcoming the inherent time scale challenge of finite temperature molecular dynamics.
Introduction Interface- or grain boundary (GB)dominated materials can exhibit extraordinary mechanical properties in terms of yield stress and ductility, particularly when the length scale associated with the interfaces approaches the sub-100 nanometer regime.1,2 Well-known examples are metallic nanocrystalline materials, which demonstrate significant increases in yield stress when the mean grain size falls below 100 nm.1–4 Particularly strong, but still deformable, microstructures also can be achieved in materials of low stacking fault energy by introducing a high density of nanoscale twins into an otherwise coarser microstructure.5,6 The mechanical response of coarsegrained polycrystals has been modeled by mesoscopic techniques such as the 3D dislocation dynamics simulation method.7–9 In these methods, traditional ideas of dislocation nucleation/multiplication via Frank-Read like dipole sources are used, in which the fundamental mechanism is the dislocation-dislocation interaction. In this regime, GBs primarily enforce plastic macroscopic compatibility, but as the 184
grain size is reduced, the role of the GB as both a dislocation source and barrier must be taken explicitly into account. Representing GBs as impenetrable barriers within the framework of 2D dislocation dynamics has constituted one strategy that begins to address these issues.10,11 The GB dislocation nucleation aspect also has been included in larger length-scale modeling methods.12–14 Such approaches all assume empirical laws whose origins are fundamentally atomistic, and it is from this perspective that molecular dynamics (MD) simulation can play an important role in the study of plasticity, since it allows for a detailed investigation of the underlying atomic scale processes that lead to dislocation nucleation, absorption, and transmission at a GB. In this article, the various aspects of the dislocation–interface interaction studied by atomistic simulation methods are reviewed, and a number of concrete examples are given spanning dislocation nucleation, propagation, absorption, and transmission at an inte
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