The interface and lamellar structures in Mg–Gd–Ag alloys investigated by experiment and first principles

The layered regions of γ''/β' and γ'' internal phases in Mg–Gd–Ag alloys have been determined using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and first-principles density functional theory (DFT) calculations. The poor rare-earth layered region (PRELR) exists between plate-like γ'' and vertical stripes β' phase precipitates. The calculation proves that the predicted morphologies between γ'' and β' precipitates are three poor rare-earth Mg layers, while the γ'' precipitates have three similar types and they have co-existence during the aged process. Moreover, these layers have two types of interfaces (γ''/Mg and Mg/β') in the structure. The Mg/β' interface is the more stable layer and bonds are stronger than the Mg/β' interface, thus the PRELR becomes part of γ'' precipitates. Therefore, the characterization and calculations of the γ'' and β' interfaces provide a theoretical basis for interface design and material analysis.