Nanocrystalline materials have been around for well over two decades. Extensive research has been conducted with the major focus on some of the extraordinary property changes and a few structure parameters such as the grain size and grain boundaries. As a result, a systematic and complete study of how the microstructures in nanoscale affect the properties has been largely ignored. Despite the scale difference, nanocrystalline materials possess the same microstructures as those in polycrystalline materials. The microstructures have statistical properties that are characterized by the topological entities of the three dimensional grains cores, two-dimensional grain boundaries, and one-dimensional junctions, and zero-dimensional vertices. Those microstructure entities contribute collectively to the properties in nanocrystalline materials.

In this talk, I will present a systematic study of the microstructures in some model nanocrystalline materials with a particular emphasis on atomistic characterizations and measurement.  A newly developed algorithm to generate realistic microstructures and the characterization tools to measure the grain cores, grain boundaries, junctions and vertices in nanoscale will be presented. The so-called digital microstructures will be examined, also with the simulated scattering from those structural entities. We show that the microstructures have intimate and complicated relations with the mechanical responses in the nanocrystalline materials. One of the conclusions we learned from this work is that we need to include as much as possible all microstructures to understand and manipulate the properties in nanocrystalline materials. Finally, the challenges and some initial efforts in connecting the digital microstructures with real experiment will be discussed.

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