Molecular-dynamics study of the synthesis and characterization of a fully dense, three-dimensional nanocrystalline material

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Abstract
A molecular‐dynamics simulation method is described that permits space‐filling, fully dense three‐dimensional nanocrystalline materials to be grown by crystallization from the melt. The method is illustrated by computer synthesis of an eight‐grain polycrystal of Cu with a grain size of 43 Å. At the beginning of the simulation, eight small pre‐oriented single‐crystal seeds are embedded in the melt which is subsequently cooled below the melting point to enable crystal growth under an applied external pressure. The fully relaxed nanocrystalline material contains large perfect‐crystal regions separated by well‐defined grain boundaries, most of which have approximately the same width and energy. In spite of the rather small number of grains in the simulation cell, the thermal expansion of the material is practically isotropic, and almost identical to that of the perfect crystal. The elastic moduli are also almost isotropic and are somewhat lower than in the coarse‐grained material. The material exhibits a low‐temperature anomaly in the specific heat.