Deformation-induced structural multiplicity of tilt boundaries facilitating the formation of two-dimensional interfacial superstructures

Understanding the interfacial structures and the induced solute segregation behaviors at the atomic scale can facilitate the design of high-performance materials. However, the diversity and concealed nature of interfaces often make it challenging to reveal the interfacial microstructures and the accompanying solute segregation phenomena. Here, we report the discovery of 8 types of asymmetric tilt grain boundaries (GBs) with solute segregation in a deformed and annealed Mg-rare-earth binary model alloy, by means of Z-contrast high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) observations. Molecular dynamics (MD) simulations provide a visual depiction of the atomic-scale characteristics of the periodic extension and compression sites in these tilt GBs. The first-principles density functional theory (DFT) calculations unveil the energetics of the well-ordered segregation behavior of solutes at these interfaces. It is confirmed that the selective segregation of solutes at substitutional sites in the periodic misfit-dislocations separated tilt GBs leads to the formation of 8 types of unique two-dimensional interfacial superstructures. Additionally, the MD simulations have revealed that solute segregation plays a pivotal role in governing the shear strength of tilt GBs by influencing the nucleation of dislocations at interfaces. Our atomic-scale insights provide valuable guidance for understanding the formation of tilt GBs within the wrought alloys and their pivotal role in facilitating solute segregation, enabling the creation of specific two-dimensional superstructures at interfaces. Furthermore, these insights hold promise for advancing the design of high-performance alloys through the application of GB engineering.