Interphase Boundary Segregation into an Ordered Core-Shell Structure with a Shell Containing Two Unit Cells

Segregation of solutes at a phase boundary or interface is ubiquitous in the multicomponent materials and has a serious effect on their mechanical properties; it is therefore becoming a more important issue. However, most of the phase boundary or interface segregations found so far happen in a disordered manner. Herein, we report an ion-milling induced ordered segregation of solutes at the phase boundary in an aged Mg-In-Ca alloy. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy observation combined with density functional theory computations indicates that the indium atoms would segregate to the nanoprecipitated-Ca2In/a-Mg phase boundary, to generate an ordered core-shell structure, in which the shell layer is identified as hexagonal close-packed Mg-In solid solution with a thickness of several nanometers containing two unit cells. This finding is interesting and important for understanding the interface segregation behaviors and is expected to provide new insights to design many important structural materials, even the surfaces functionalization of materials.