Segregation of solute atoms in Mg–Ce binary alloy: atomic-scale novel structures observed by HAADF-STEM

In the present study, the segregation of solute atoms from α-Mg solid solution phase in Mg–3Ce (wt.%) alloys is investigated by means of atomic-scale high angle annular dark field – scanning transmission electron microscopy. The segregation behaviours, featured by different metastable nanoscale structures, are basically categorised into two types. In type-I segregation, solute atoms occupy certain lattice sites in the α-Mg phase and form linearly outlined structures. In type-II segregation, solute Ce atoms form pure FCC structures with lattice parameters equivalent to 5.52 Å. In addition to the two types of segregation that exist in a large amount, a peculiar round-like enrichment structure of Ce is characterised, in which Ce-enriched clusters align along Mg and Mg directions and form the round-like shape when viewed as a whole.