Abstract
First-principles density functional calculations are used to study the nucleation and stability of L12-ordered precipitates in Al-Sc-Li alloys. For dilute Al alloys, there are three possible ordered L12 precipitates: Al3Sc, Al3Li and an Al3Sc/Al 3Li core/shell structure. To calculate the nucleation behavior, information about bulk thermodynamics (both static total energies and vibrational free energies), interfacial energetics and coherency strain is required. The study finds the following: (1) the coherency strain energies for forming coherent interfaces between Al/Al3Sc, Al/Al3Li and Al3Sc/Al3Li are relatively small, owing to the small atomic size mismatches in these systems; (2) the sublattice site preferences of Sc and Li are calculated, and it is demonstrated that Sc and Li share the same sublattice sites in both Al3Sc(L12) and Al 3Li(L12), in agreement with recent experimental results; (3) the calculated solubilities of Sc and Li in α-Al alloys are in good agreement with experimental values and, for Sc, agree well with prior first-principles results; (4) the interfacial energies for Al/Al3Sc, Al/Al3Li and Al3Sc/Al3Li for (1 0 0), (1 1 0) and (1 1 1) interfaces are calculated: the values of the Al/Al3Sc interfacial energies are significantly larger than those of the Al/Al 3Li and Al3Sc/Al3Li interfaces; (5) combining the bulk and interfacial energies yields the nucleation barriers and critical radii for Al3Sc and Al3Li precipitates; and (6) the energetic stability of the Al3Sc/Al3Li core/shell structure is compared with individual Al3Sc and Al3Li nuclei, and the range of precipitate sizes for which the core/shell structure is energetically favored is determined quantitatively.
Original language | English (US) |
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Pages (from-to) | 3012-3023 |
Number of pages | 12 |
Journal | Acta Materialia |
Volume | 59 |
Issue number | 8 |
DOIs | |
State | Published - May 2011 |
Funding
This work is supported by the Department of Energy, Office of Basic Energy Science, under Grant DE-FG02-98ER45721, monitored by Dr. John Vetrano. Wei Chen is supported by National Science Foundation under Contracts No. CBET-0730841 and No. CBET-0731020 . The authors thank Prof. David C. Dunand for many helpful discussions, and Mr. Matthew E. Krug and Dr. Christopher Booth-Morrison for discussions of the APT results.
Keywords
- Al-Sc-Li
- Core/shell structures
- First principles
- Interfacial energy
- Site substitution
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys