Transmission Electron Microscopy for Precipitate Phases in Rapidly Solidified Mg-2 at%Ce-1 at%Zn and Mg-2 at%Ce Alloys

Precipitate phases in Mg-2 at%Ce-1 at%Zn (Mg97Ce2Zn1) and Mg-2 at%Ce (Mg98Ce2) alloys, prepared by a melt-quenching method, have been examined by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). A precipitate phase formed at grain boundaries has an ordered structure with a hexagonal unit cell of root 13a(0) and c(0), in which a(0) and c(0) are lattice parameters of an h.c.p. structure of the Mg-matrix. On the other hand, a precipitate phase embedded in Mg-matrix grains has a long-period modulated structure formed by the appearance of two-dimensional anti-phase boundaries with a hexagonal symmetry in the fundamental hexagonal structure with lattice constants of root 3a(0) and c(0).