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. 2018 Oct 12;4(10):eaat8712.
doi: 10.1126/sciadv.aat8712. eCollection 2018 Oct.

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

Zhiqiang Fu  1   2 , Lin Jiang  2   3 , Jenna L Wardini  2 , Benjamin E MacDonald  2 , Haiming Wen  4 , Wei Xiong  5 , Dalong Zhang  2 , Yizhang Zhou  2 , Timothy J Rupert  2 , Weiping Chen  1 , Enrique J Lavernia  2
Affiliations

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

Zhiqiang Fu et al. Sci Adv. .

Abstract

High-entropy alloys (HEAs) are a class of metallic materials that have revolutionized alloy design. They are known for their high compressive strengths, often greater than 1 GPa; however, the tensile strengths of most reported HEAs are limited. Here, we report a strategy for the design and fabrication of HEAs that can achieve ultrahigh tensile strengths. The proposed strategy involves the introduction of a high density of hierarchical intragranular nanoprecipitates. To establish the validity of this strategy, we designed and fabricated a bulk Fe25Co25Ni25Al10Ti15 HEA to consist of a principal face-centered cubic (fcc) phase containing hierarchical intragranular nanoprecipitates. Our results show that precipitation strengthening, as one of the main strengthening mechanisms, contributes to a tensile yield strength (σ0.2) of ~1.86 GPa and an ultimate tensile strength of ~2.52 GPa at room temperature, which heretofore represents the highest strength reported for an HEA with an appreciable failure strain of ~5.2%.

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Figures

Fig. 1
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
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
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
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
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.
See this image and copyright information in PMC

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