Characterization of β′ Precipitate Phase in Mg-2 at%Y Alloy Aged to Peak Hardness Condition by High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM)

Abstract

The β′ phase precipitated in an Mg-2 at%Y (Mg₉₈Y₂) alloy aged to a peak hardness condition at 200°C for 336 h has been studied by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). The β′ precipitates have an about 20 nm size and definite facets parallel to the (010) plane, and Y-enriched double atom planes parallel to the (010) plane grow long and sometimes individually along the [100] and [001] directions. This morphology of the β′ precipitates in the Mg₉₈Y₂ alloy is remarkably different from that in an Mg₉₅Gd₅ alloy.