Thermodynamic stability of Mg-based ternary long-period stacking ordered structures

James E. Saal*, C. Wolverton

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

88 Scopus citations

Abstract

Mg alloys containing long-period stacking ordered (LPSO) structures exhibit remarkably high tensile yield strength and ductility. They have been found in a variety of ternary Mg systems of the general form Mg-XL-X S, where XL and XS are elements larger and smaller than Mg, respectively. In this work, we examine the thermodynamic stability of these LPSO precipitates with density functional theory, using a newly proposed structure model based on the inclusion of a Mg interstitial atom. We predict the stabilities for 14H and 18R LPSO structures for many Mg-X L-XL ternary systems: 85 systems consisting of X L = rare earths (RE) Sc, Y, La-Lu and XS = Zn, Al, Cu, Co, Ni. We predict thermodynamically stable LPSO phases in all systems where LPSO structures are observed. In addition, we predict several stable LPSO structures in new, as-yet-unobserved Mg-RE-XS systems. Many non-RE XL elements are also explored on the basis of size mismatch between Mg and X L, including Tl, Sb, Pb, Na, Te, Bi, Pa, Ca, Th, K, Sr - an additional 55 ternary systems. XL = Ca, Sr and Th are predicted to be most promising in terms of forming stable LPSO phases, particularly with X S = Zn. Lastly, several previously observed trends amongst known XL elements are examined. We find that favorable mixing energy between Mg and XL on the face-centered cubic lattice and the size mismatch together serve as excellent criteria determining XL LPSO formation.

Original languageEnglish (US)
Pages (from-to)325-338
Number of pages14
JournalActa Materialia
Volume68
DOIs
StatePublished - Apr 15 2014

Keywords

  • Density functional theory
  • LPSO
  • Magnesium alloys
  • Phase diagram
  • Phase stability

ASJC Scopus subject areas

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

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