Three-dimensional observations of grain volume changes during annealing of polycrystalline Ni

The orientations, locations, and sizes of approximately 2500 grains in a Ni polycrystal were measured at six points in time during an interrupted annealing experiment by synchrotron x-ray based, near field high-energy diffraction microscopy. The volume changes were compared to the geometric characteristics of the grains in both the original microstructures and microstructures in which adjacent twin related domains were merged. Neither the size of a grain nor the number of its nearest neighbors correlates strongly to a grain's volume change over the time scale of this experiment. However, the difference between the number of neighbors a grain has, F, and the average number of neighbors of the neighboring grains have, < F-NN >, is correlated to the volume change. A grain with more (fewer) neighbors than < F-NN > usually grows (shrinks). The correlation between the volume change and F - < F-NN > is obvious only if adjacent twin related domains are merged. The correct sign of the volume change is predicted by F - < F-NN > about two thirds of the time. The results show that the volume change for a given grain is better predicted by comparing a grain's characteristics to its neighbor's characteristics than to the characteristics of the entire ensemble of grains. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.