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First-principles investigation of the phase stability and early stages of precipitation in Mg-Sn alloys

Kang Wang, Du Cheng, Chu-Liang Fu, and Bi-Cheng Zhou
Phys. Rev. Materials 4, 013606 – Published 28 January 2020
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Abstract

Recently, remarkable experimental progress has been made toward understanding the metastable phases in Mg-Sn alloys, a promising candidate for rare-earth free Mg alloys. However, the detailed structures, stability, and formation mechanisms of these metastable phases at early stages of precipitation remain unclear. Here, we report a first-principles study of the ground-state and finite-temperature phase stability of hexagonal closest packed (HCP)- and face-centered cubic (FCC)-based phases in Mg-Sn alloys. The ground-state phases are searched by the cluster expansion approach coupled with energy input from first-principles calculations. The Monte Carlo simulations with Hamiltonian from the cluster expansion are performed to calculate the configurational free energies and the corresponding metastable phase diagrams are constructed. Our calculations reveal rich varieties of orderings on HCP and FCC lattices, metastable Mg3Sn phases with L12 and D019 structures, and possible precursors for Guinier-Preston (G.P.) zones. Further analysis of the vibrational free energy indicates that L12 Mg3Sn is stabilized by vibrational entropy at high temperatures. A new precipitation sequence for Mg-Sn alloys is suggested, i.e., supersaturated solid solution → G.P. zone → D019 Mg3SnL12 Mg3SnβMg2Sn.

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  • Received 29 August 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.4.013606

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Kang Wang, Du Cheng, Chu-Liang Fu, and Bi-Cheng Zhou*

  • Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, USA

  • *bicheng.zhou@virginia.edu

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Issue

Vol. 4, Iss. 1 — January 2020

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