Polytypes of long-period stacking structures synchronized with chemical order in a dilute Mg-Zn-Y alloy

TL;DR

This study identifies and characterizes long-period stacking polytypes in a dilute Mg-Zn-Y alloy, revealing synchronized chemical and stacking order with potential implications for alloy properties.

Contribution

It uncovers new long-period stacking derivatives with chemical order in Mg-Zn-Y alloys, combining atomic-resolution imaging and structural analysis.

Findings

Identified structural polytypes with long-period stacking in Mg-Zn-Y alloy.

Revealed chemical order synchronized with stacking faults.

Demonstrated enrichment of Zn/Y atoms in specific layers.

Abstract

A series of structural polytypes formed in an Mg-1at.%Zn-2at.%Y alloy has been identified, which are reasonably viewed as long-period stacking derivatives of the hcp Mg structure with alternate AB stacking of the close-packed atomic layers. Atomic-resolution Z-contrast imaging clearly revealed that the structures are long-period chemical-ordered as well as stacking-ordered; unique chemical order along the stacking direction occurs as being synchronized with a local faulted stacking of AB'C'A, where B' and C' layers are commonly enriched by Zn/Y atoms.