Grain boundary migration in polycrystalline $\alpha$-Fe

TL;DR

This study uses high energy x-ray diffraction microscopy to analyze grain boundary migration in polycrystalline alpha-iron, revealing complex migration behaviors influenced by boundary energy and motion components, challenging traditional assumptions.

Contribution

It provides detailed measurements of grain boundary properties and uncovers new insights into the mechanisms driving boundary migration beyond curvature effects.

Findings

Boundary velocities are not correlated with the product of curvature and energy.

Low energy boundaries tend to expand, high energy boundaries tend to shrink.

Both lateral and normal boundary motions contribute to migration.

Abstract

High energy x-ray diffraction microscopy was used to image the microstructure of $\alpha$-Fe before and after a 600 $^\circ$C anneal. These data were used to determine the areas, curvatures, energies, and velocities of approximately 40,000 grain boundaries. The measured grain boundary properties depend on the five macroscopic grain boundary parameters. The velocities are not correlated with the product of the mean boundary curvature and grain boundary energy, usually assumed to be the driving force. Boundary migration is made up of area changes (lateral motion) and translation (normal motion) and both contribute to the total migration. Through the lateral motion component of the migration, low energy boundaries tend to expand in area while high energy boundaries shrink, reducing the average energy through grain boundary replacement. The driving force for this process is not related to curvature and might disrupt the expected curvature-velocity relationship.