Chemistry and structure of core/double-shell nanoscale precipitates in Al-6.5Li-0.07Sc-0.02Yb (at.%)

Christian Monachon, Matthew E. Krug, David N Seidman, David C Dunand

Research output: Contribution to journalArticle

33 Scopus citations

Abstract

An Al-6.3Li-0.07Sc-0.02Yb (at.%) alloy is subjected to a double-aging treatment to create nanoscale precipitates, which are studied by atom-probe tomography and transmission electron microscopy. After homogenization and quenching, Yb atoms form clusters exhibiting L12-like order. A first aging step at 325 °C leads to a doubling of microhardness as a result of the formation of coherent precipitates with an Al3Yb-rich core and an Al3Sc-rich shell. The core and shell both exhibit the L12 structure and both contain a large concentration of Li, which substitutes for up to 50% of the Sc or Yb atoms at their sublattice positions. These core/single-shell precipitates provide excellent resistance to overaging at 325 °C. Subsequent aging at 170 °C increases the microhardness by an additional 30%, through precipitation of a metastable δ′-Al 3Li second shell on the core/single-shell precipitates, thereby forming a chemically and structurally complex core/double-shell structure. The metastable δ′-Al3Li phase is observed to form exclusively on pre-existing core/shell precipitates.

Original languageEnglish (US)
Pages (from-to)3398-3409
Number of pages12
JournalActa Materialia
Volume59
Issue number9
DOIs
StatePublished - May 1 2011

Keywords

  • Aluminum alloys
  • L1
  • Precipitation strengthening
  • Rare earth
  • Scandium

ASJC Scopus subject areas

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

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