Microstructural characterization in 3D-the key to understanding grain growth in polycrystalline materials?

摘要

During grain growth, larger grains tend to grow at the expense of their smaller neighbors, resulting in a steady increase in the average crystallite size. Because the growth rate of any given grain is affected by that of its neighbors, the manner in which growth occurs is determined to a large extent by correlations in the sizes of neighboring grains. Quantitative information concerning these correlations can be extracted only from a truly three-dimensional characterization of the sample microstructure. We have used x-ray microtomography to measure the nearest-neighbor size correlations in a polycrystalline specimen of Al alloyed with 2 at.% Sn. The tin atoms segregate to the grain boundaries, where they impart a strong contrast in x-ray attenuation that can be reconstructed tomographically. From such reconstructions, we measured the size, topology and local connectivity of nearly 5000 contiguous Al grains and subsequently computed the size correlations in this material. The resulting information was incorporated into a non-mean-field theory for grain growth, the accuracy of which could be evaluated by comparing its predictions to the observed microstructure of the Al-Sn samples.