Thermodynamic origin of solute-enriched stacking-fault in dilute Mg-Zn-Y alloys

M. Egami, I. Ohnuma, M. Enoki, H. Ohtani, E. Abe

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)

Abstract

We have investigated thermodynamic behaviors of dilute Mg-Zn-Y ternary alloys to form a unique solute-enriched stacking-fault (SESF), which is an intrinsic-II type stacking-fault (I2-SF) enriched by the Zn and Y atoms and represents the structural-unit of the long-period stacking/order (LPSO) phase. SESF in the hexagonal-close-packed (hcp) Mg matrix forms a local face-centered-cubic (fcc) environment, and hence our thermodynamic analysis is based on the Gibbs energy comparison between hcp and fcc phases over the Mg-Zn-Y ternary composition ranges, using the calculation of phase diagrams (CALPHAD) method aided by the first principles calculations. We find that the Zn/Y co-segregations at the SESF provide a remarkable condition that the fcc layers become more stable than the hcp-Mg matrix. Furthermore, within the SESF, the following spinodal-like decomposition into the Mg-rich solid-solution and the Zn/Y-rich L12-type order phase causes a significant reduction of the total Gibbs energy of the system. These spontaneous thermodynamic behaviors explain why the fault layers can be remarkably stabilized in the LPSO-forming ternary Mg alloys, and also support a phenomenological origin of the Zn-Y clustering with the L12-type short-range order, which is known to occur for the LPSO phases and has been confirmed for the present SESF by electron microscopy experiments.

Original languageEnglish
Article number108452
JournalMaterials and Design
Volume188
DOIs
Publication statusPublished - 2020 Mar

Keywords

  • Calculation of phase diagrams (CALPHAD)
  • Magnesium alloys
  • Scanning transmission electron microscopy
  • Solute-atom clustering
  • Thermodynamic analysis

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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