Formation of giant atomic clusters in the β-Samson (β-Al3Mg2) phase of the Al-Mg alloy system

Kei Nakayama, Hijiri Tsuruta, Yasumasa Koyama

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    Abstract

    The crystallographic features of the (α-Mn → α-Mn + β-Samson) reaction in Al-Mg alloys around the composition of 48 at.% Mg have been investigated mainly by transmission electron microscopy to understand the formation of giant atomic clusters in the β-Samson structure. It was confirmed, for instance, that the state of an Al-48 at.% Mg alloy annealed at 573 K for 24 h could be identified as the (α-Mn + β-Samson) coexistence state, and that metastable states were found locally in α-Mn/β-Samson boundary regions. An analysis of electron diffraction patterns obtained from the coexistence state indicated that the orientation relationship of (3¯ 30)α//(8¯ 80)β-S and [110]α//[110]β-S was established between α-Mn and β-Samson regions, together with a lattice contraction of about 10% along the [001]α direction and an expansion of about 0.4% along the [1¯ 10]α direction in the (α-Mn → β-Samson) structural change. High-resolution electron micrographs of the coexistence state also suggested that some atoms at the Mg (I) and Mg (II) sites in the distorted α-Mn structure could be converted to those at the Mg (23) site of the β-Samson structure as the center site of the Samson cluster. Furthermore, both the features of giant clusters in the β-Samson structure and their formation from the α-Mn structure were discussed on the basis of the experimental data obtained in this study.

    Original languageEnglish
    Pages (from-to)249-257
    Number of pages9
    JournalActa Materialia
    Volume128
    DOIs
    Publication statusPublished - 2017 Apr 15

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    Keywords

    • Intermetallic compounds
    • MgAl alloys
    • Samson cluster
    • Transmission electron microscopy

    ASJC Scopus subject areas

    • Electronic, Optical and Magnetic Materials
    • Ceramics and Composites
    • Polymers and Plastics
    • Metals and Alloys

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