Energetics of native defects, solute partitioning, and interfacial energy of Q precipitate in Al-Cu-Mg-Si alloys

Kyoungdoc Kim, Andrew Bobel, Vuk Brajuskovic, Bi Cheng Zhou, Mike Walker, G. B. Olson, C. Wolverton*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The compound Al3Cu2Mg9Si7, is known as the Q-phase and forms as a thermodynamically stable precipitate during aging in the quaternary Al-Cu-Mg-Si system. We perform atomic-scale density functional theory (DFT) calculations of defect properties, solute partitioning, and interfacial stability of the Al3Cu2Mg9Si7 (Q) precipitate. We find: (i) simple native point defect (i.e., vacancies and anti-sites) thermodynamics can partially explain the experimentally observed off-stoichiometry, such as the observed variation of compositions, Al3+δCu2Mg9-δSi7 (Mg-deficient and Al-rich) in experiment. (ii) Calculated solute-partitioning energies of common solutes allow us to define general rules for site-preference in the Q-phase in terms of electronic structure and atomic radius. To validate our DFT predictions, we perform atom-probe tomography (APT) experiments for six-different elements (Zn, Ni, Mn, Ti, V, and Zr). The results show that the partitioning behavior of solutes Ni, Zn, and Mn are consistent with DFT predictions, but the transition elements (Ti, V, and Zr), which are anomalously slow diffusers in Al, partition to the Q-phase in constrast to DFT partitioning energies. (iii) For the low energy interface (112¯0)Q//(510)Al observed in needle shaped Q-precipitate, we survey various terminations and orientations and derive a low-energy interfacial structure. We find this low-energy interfacial model has Cu atoms nearest to the interface, which is in agreement with previous literature on Cu interfacial segregation at the Q′//α-Al interface. The computed interfacial energy (0.52 J/m2) and the corresponding structure will be useful input to future multi-scale modeling of microstructural evolution.

Original languageEnglish (US)
Pages (from-to)207-219
Number of pages13
JournalActa Materialia
Volume154
DOIs
StatePublished - Aug 1 2018

Funding

K. K. and A. B. (DFT calculations and 3DAP experiments) acknowledge support from the U.S. Department of Energy under award number DE-EE0006082 . B. C. Z. (advice and collaboration on DFT calculations and writing manuscript) acknowledges support from Beijing International Aeronautical Materials Corp. (BIAM) . G. O. and C. W. (overall leadership of project and design of calculations and experiments) were supported by The Center for Hierarchical Materials Design (CHiMaD), Dept. of Commerce, NIST under award number 70NANB14H012 . We gratefully acknowledge the computing resources from Quest high performance facility and the National Energy Research Scientific Computing (NERSC) Center , a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 . This work made use of the Northwestern University Center for Atom-Probe Tomography (NUCAPT) facility. Funding for the purchase of the LEAP tomography and for upgrades was generously provided by NSF-MRI ( DMR 0420532 ), ONR-DURIP ( N00014-0400798 ) and ONR-DURIP ( N00014-0610539 ).

Keywords

  • Aluminum alloys
  • Atom-Probe Tomography (APT)
  • Density Functional Theory (DFT)
  • First-principles calculation
  • Q-phase precipitates

ASJC Scopus subject areas

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

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