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 alpha-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 alpha-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 angstrom. 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 < 1 0 (1) over bar 0 >(Mg) and < 1 1 (2) over bar 0 >(Mg) directions and form the round-like shape when viewed as a whole.