Effects of W and Si microadditions on microstructure and the strength of dilute precipitation-strengthened Al–Zr–Er alloys

Amir R. Farkoosh*, David C. Dunand, David N. Seidman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

The effect of single or combined micro-additions of tungsten (0.03 at.%) and silicon (0.02–0.40 at.%) on the evolution of Al3(Zr,Er) (L12) nanoprecipitates in a cast Al-0.11Zr-0.005Er (at.%) alloy is investigated utilizing isochronal (200–600 °C) and isothermal (400, 425 and 450 °C) aging treatments. Atom-probe tomography measurements reveal that the slow-diffusing W, upon aging, partitions to the L12-nanoprecipitates (average composition of 0.11–0.37 at.% W; partitioning ratio of 5–12), without altering their crystal structure or spheroidal morphology, as confirmed by transmission electron microscopy. First-principles calculations indicate that W occupies the Al sublattice sites of Al3Zr(L12), leading to a small increase in the lattice parameter of the nanoprecipitates. In the low-Si (0.02 at.%) alloys, the precipitation and coarsening kinetics of nanoprecipitates are unaffected by W additions. A small enhancement in nanoprecipitate coarsening resistance is achieved, however, by W additions in the high-Si (0.4 at.%) alloys. The W-modified alloys exhibit significant improvements in compressive creep resistance at 300 °C; the threshold stress increases from 11 MPa in the W-free alloy to 15 and 16 MPa in the low-Si and high-Si alloys with W additions, respectively. This is explained by an increased lattice parameter mismatch between the L12-nanoprecipitates and the matrix, due to Er enrichment in the nanoprecipitates in the presence of W. Silicon additions, in alloys with and without W, lead to a higher peak microhardness (ΔHV ~90–110 MPa) and higher creep threshold stresses (Δσth ~2–4 MPa) by increasing the L12-nanoprecipitate number density, but at the expense of their long-term coarsening resistance.

Original languageEnglish (US)
Article number140159
JournalMaterials Science and Engineering A
Volume798
DOIs
StatePublished - Nov 4 2020

Keywords

  • Coarsening kinetics
  • Creep resistance
  • High-temperature aluminum alloys
  • Mechanical properties
  • Scandium
  • Zirconium

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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