| Abstract Scope |
Optimizing the properties of polycrystalline materials requires significant microstructural design, which hinges on our understanding of grain growth. However, studies on grain growth have focused mostly on the average properties of the system (grain size and growth rate) while ignoring the contributions of local properties (geometric, topological and network effects). The latter can only be measured reliably in three dimensions. Additionally, in thin specimens, the crystallographic distribution of internal grain surfaces is strongly influenced by the free surfaces. Understanding what lies beneath the surface naturally requires 3D characterization. To this end, developments in laboratory-based X-ray diffraction contrast tomography (DCT) have enabled us to study the temporal evolution of an unprecedented 10,000 grains in a thin aluminum disc sample upon annealing, where the sample thickness is ~5x the initial grain diameter. Armed with this data, we firstly test the validity of the Lewis, von Neumann-Mullins, and the Aboav-Weaire laws for the ensemble of interior and surface-touching grains in this specimen. The large volume of data is also conducive to a study of rare events like abnormal grain growth, helping us pinpoint the conditions that may cause a grain to grow abnormally. Finally, to understand the influence of free surfaces on the crystallographic distribution of grain boundary planes within the specimen, we computed the grain boundary character and plane distributions. Our analysis of surface and bulk grain boundary planes over time explores how curvature, crystallography, and free surface effects influence and constrain grain and grain boundary evolution. These insights deepen our understanding of microstructure evolution in thin samples. |