A Novel Fe-enriched Lamella Sandwich Precipitate Formed in A Mg-Gd-Fe Alloy

Abstract

A novel Fe-enriched lamella sandwich phase (χ-phase) has been found to precipitate along the basal (0001)_Mg planes in the heat-treated Mg-Gd-Fe alloy and its structure is clearly revealed by means of atomic-resolution transmission electron microscopy. The layered χ-phase only has a thickness of mono-unit-cell and consists invariably of ten atomic layers stacking along the [0001]_Mg direction, of which the outermost atomic layers had larger in-plane atom-pillar spacing than the inner layers. Fe/Gd atoms are mainly enriched in the outer four atomic layers in the χ-phase, forming two structurally unsymmetrical four-layer shells to sandwich the middle two Mg layers. An atomic model has been proposed for this layered sandwich-structured χ-phase.

Keywords

Mg-Gd-Fe alloys / microstructure / Fe-enriched precipitate / lamella sandwich phase