An atomic scale characterization of a novel basal plate with a close-packed structure in Mg-Nd-In alloys

Abstract

In Mg-Nd-In alloy, the conventional β′ strengthening phase has been replaced by a basal plate with an introduction of In atom. In this work, the basal plate is elucidated to have a ternary composition and a close-packed structure using atomic scale scanning transmission electron microscopy. The stacking layer containing three parallel (0001)α atomic planes is stacked alternately and the two adjacent stacking layers have a 180° rotational symmetry along [0001]α, constituting a perfect hexagonal stacking structure with an AoBrAoBr stacking sequence. It is confirmed that the hexagonal structure has a space group P6322 and parameter lattices of aH = 1.134 nm and cH = 1.606 nm. However, in case that a 180° rotation does not occur between two stacking layers, a stacking fault or a rhombohedral configuration of an AoBrAoCoAr stacking sequence can appear. In addition, the basal plate generally has a thickness of less than 40 nm and an aspect ratio of ~20, as well as can maintain a specific orientation relationship to α-Mg matrix, which are also discussed particularly based on the interfacial mismatch between both phases.