Prediction and characterization of an Mg-Al intermetallic compound with potentially improved ductility via orbital-free and Kohn-Sham density functional theory

Houlong Zhuang, Mohan Chen, Emily A. Carter

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

Magnesium-aluminum (Mg-Al) intermetallic compounds that form as precipitates can significantly influence the mechanical properties of Mg-Al alloys. A computational evaluation of known and unknown Mg-Al intermetallic compounds could help design new Mg-Al alloy microstructures with optimal properties. Here, we employ the cluster-expansion method with energies efficiently calculated with orbital-free density functional theory (OFDFT) and predict a new, metastable intermetallic compound Mg3Al with a D019 hexagonal structure that is slightly more stable than an alternative L12 cubic structure. We apply Kohn-Sham DFT (KSDFT) to accurately evaluate various metastability criteria for D019 and L12 Mg3Al, including Born's criterion and phonon dispersion. We show that both Mg3Al crystalline phases satisfy the metastability criteria and hence should be at least metastable. We further compare ductility metrics for D019 and L12 Mg3Al to that of hexagonal-close-packed Mg by computing Pugh's ratio and generalized stacking fault energies. The ductility is predicted to follow the order: D019 Mg3Al > L12 Mg3Al > Mg, based on the highest Pugh's ratio and the lowest unstable stacking and twinning fault energies of D019 Mg3Al compared to that of Mg. We also predict a very low antiphase boundary energy for Mg3Al and therefore expect D019 Mg3Al to be beneficial for improving the ductility of Mg-rich Mg-Al alloys. A computational design of Mg-Al alloy microstructures may become possible by combining the strengths of both OFDFT and KSDFT, i.e., the efficiency of the former and the accuracy of the latter, as demonstrated here.

Original languageEnglish (US)
Article number075002
JournalModelling and Simulation in Materials Science and Engineering
Volume25
Issue number7
DOIs
StatePublished - Aug 16 2017
Externally publishedYes

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Keywords

  • composition
  • crystal structure
  • ductility
  • elastic modulus
  • firstprinciples calculations

ASJC Scopus subject areas

  • Modeling and Simulation
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Computer Science Applications

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