Comments on 'Revisiting building block ordering of long-period stacking ordered structures in Mg-Y-Al alloys'

TL;DR

This paper critiques a recent study on LPSO structures in Mg-Y-Al alloys, clarifying the nature of building clusters and providing experimental evidence for domain structures in related alloys.

Contribution

It clarifies the origin of proposed metastable clusters and presents experimental evidence for domain structures in Mg-Al-Gd alloys.

Findings

New cluster types are due to superimposition in different domains

Experimental evidence supports domain structures in Mg-Al-Gd alloys

Reassessment of previous interpretations of LPSO structures

Abstract

In a recent paper, Zhang et al. [Acta Materialia 152 (2018) 96] studied the in-plane ordering of the long-period stacking ordered (LPSO) structure in Mg-Al-Y alloys. In addition to the well-known L12 type building cluster, they proposed three new types of metastable building clusters. However, we will show that these new types of building clusters are caused by the superimposition of L12 type clusters located in different domains. In addition, the experimental evidence for domain structures in a similar alloy system Mg-Al-Gd is provided.