Research ArticleENGINEERING

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

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Science Advances  12 Oct 2018:
Vol. 4, no. 10, eaat8712
DOI: 10.1126/sciadv.aat8712
  • Fig. 1 X-ray scattering and EBSD analyses of the bulk Fe25Co25Ni25Al10Ti15 HEA.

    (A) XRD pattern. (B) Statistics of grain diameters for the two phases were collected on the basis of EBSD and TEM images. (C) EBSD phase map. (D) EBSD IPF corresponding to the EBSD phase map in (C).

  • Fig. 2 Microstructure of the bulk Fe25Co25Ni25Al10Ti15 HEA.

    (A) Bright-field TEM image and SAED patterns corresponding to grains a and b. (B) High density of γ′ nanoprecipitates inside the fcc phase. (C) Bright-field TEM image of a γ′ nanoprecipitate showing some secondary γ* (as indicated by the arrows) nanoprecipitates inside. (D) Schematic diagram shows the microstructure of the alloy, indicating that fcc γ matrix grains (blue) have hierarchical intragranular precipitates, i.e., primary γ′ precipitates (orange) and secondary γ* precipitates (white), and that there are some twins in the fcc grains.

  • Fig. 3 In situ SEM microtensile testing of the bulk Fe25Co25Ni25Al10Ti15 HEA.

    (A) Representative tensile engineering stress-strain curve of the SPS-consolidated sample at room temperature. (B) Corresponding tensile coupon having a cylindrical gauge section with a 4-μm diameter and a 12-μm length between electron beam–deposited Pt reference markers.

  • Fig. 4 HRTEM images of the fcc phase containing hierarchical intragranular nanoprecipitates.

    (A) Schematic diagram of coherently hierarchical nanoprecipitates in the fcc phase. (B) HRTEM image of the fcc γ matrix and two γ′ precipitates. (C) IFFT of the square area (the γ matrix) in (B) with corresponding FFT presented in the inset. (D) IFFT of the γ′ precipitate 1 in (B) with corresponding FFT presented in the inset. (E) Bright-field TEM image of the γ, γ′, and γ* phases. (F) HRTEM image of the circled area in (E). (G) IFFT of the square area indicated by solid line (the γ′ precipitate) in (F) with corresponding FFT presented in the inset. (H) IFFT of the square area indicated by dashed lines (the γ* precipitate) in (F) with corresponding FFT in the inset.

  • Fig. 5 Tensile strength-failure strain plot of selected HEAs.

    It reveals that the bulk Fe25Co25Ni25Al10Ti15 HEA shows the highest tensile strength in comparison with available literature data for HEAs having high tensile strength.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/10/eaat8712/DC1

    Alloy design strategy

    Fig. S1. TEM of the bulk Fe25Co25Ni25Al10Ti15 HEA.

    Fig. S2. Twins in the primary fcc phase.

    Fig. S3. HRTEM images of hierarchical precipitates.

    Fig. S4. Sequential snapshots from a video recorded during the in situ TEM compression test.

    Fig. S5. Fracture morphology after in situ SEM microtensile testing.

    Fig. S6. X-ray scattering and microstructure of the Fe25Co25Ni25Al10Ti15 HEA powders.

    Fig. S7. The Scheil-Gulliver simulation of the nonequilibrium fcc phase region.

    Fig. S8. SEM micrograph of the microforce sensor’s flat probe tip with custom-milled tensile grip geometry.

    Table S1. EDS/TEM and EDS/STEM results of the phases in the bulk Fe25Co25Ni25Al10Ti15.

    Table S2. Processing routes and microstructures of selected HEAs.

    Movie S1. During the initial deformation, dislocations were first generated in the γ matrix, and as the displacement increased, dislocations sheared the hierarchical γ′ and γ* precipitates.

  • Supplementary Materials

    The PDF file includes:

    • Alloy design strategy
    • Fig. S1. TEM of the bulk Fe25Co25Ni25Al10Ti15 HEA.
    • Fig. S2. Twins in the primary fcc phase.
    • Fig. S3. HRTEM images of hierarchical precipitates.
    • Fig. S4. Sequential snapshots from a video recorded during the in situ TEM compression test.
    • Fig. S5. Fracture morphology after in situ SEM microtensile testing.
    • Fig. S6. X-ray scattering and microstructure of the Fe25Co25Ni25Al10Ti15 HEA powders.
    • Fig. S7. The Scheil-Gulliver simulation of the nonequilibrium fcc phase region.
    • Fig. S8. SEM micrograph of the microforce sensor’s flat probe tip with custom-milled tensile grip geometry.
    • Table S1. EDS/TEM and EDS/STEM results of the phases in the bulk Fe25Co25Ni25Al10Ti15.
    • Table S2. Processing routes and microstructures of selected HEAs.

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). During the initial deformation, dislocations were first generated in the γ matrix, and as the displacement increased, dislocations sheared the hierarchical γ′ and γ* precipitates.

    Files in this Data Supplement:

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