Study on a novel orientation domain of Mg17Ce2 in aged Mg-Y-Ce alloy by HAADF-STEM

After solid solution and aging treatment, Mg-3.0 wt%Y-1.0 wt%Ce ternary alloys were characterized using high angle annular dark field scanning transmission electron microscopy. The main precipitates are dominated by β′ phase and Mg17Ce2, a Ni17Th2-type intermetallic compound. An orientation domain can be discerned generally in Mg17Ce2 granules. This domain structure of Mg17Ce2 always consists of two types of domains (defined as domain-Ι and domain-Π) with a 90 degree orientation difference. In terms of crystallographic orientation relationships among α-Mg matrix and both domains, the domain-Ι is parallel to α-Mg matrix, whereas, the domain-Π is perpendicular to α-Mg matrix. It can be certain that a 1¯010 direction is an unchanged orientation. Due to nearly equal values of lattice parameters (a and c) of Mg17Ce2, both domain-Ι and domain-Π can matches well with α-Mg matrix. Comparatively, the interfacial matching between domain-Ι and α-Mg matrix is better, suggesting that the domain-Ι is dominant.