Atomic-scale compositional characterization of a nanocrystalline AlCrCuFeNiZn high-entropy alloy using atom probe tomography

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We have studied a nanocrystalline AlCrCuFeNiZn high-entropy alloy synthesized by ball milling followed by hot compaction at 600 degrees C for 15 min at 650 MPa. X-ray diffraction reveals that the mechanically alloyed powder consists of a solid-solution body-centered cubic (bcc) matrix containing 12 vol.% face-centered cubic (fcc) phase. After hot compaction, it consists of 60 vol.% bcc and 40 vol.% fcc. Composition analysis by atom probe tomography shows that the material is not a homogeneous fcc-bcc solid solution but instead a composite of bcc structured Ni-Al-, Cr-Fe- and Fe-Cr-based regions and of fcc Cu-Zn-based regions. The Cu-Zn-rich phase has 30 at.% Zn alpha-brass composition. It segregates predominantly along grain boundaries thereby stabilizing the nanocrystalline microstructure and preventing grain growth. The Cr- and Fe-rich bcc regions were presumably formed by spinodal decomposition of a Cr-Fe phase that was inherited from the hot compacted state. The Ni-Al phase remains stable even after hot compaction and forms the dominant bcc matrix phase. The crystallite sizes are in the range of 20-30 nm as determined by transmission electron microscopy. The hot compacted alloy exhibited very high hardness of 870 +/- 10 HV. The results reveal that phase decomposition rather than homogeneous mixing is prevalent in this alloy. Hence, our current observations fail to justify the present high-entropy alloy design concept. Therefore, a strategy guided more by structure and thermodynamics for designing high-entropy alloys is encouraged as a pathway towards exploiting the solid-solution and stability idea inherent in this concept. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Publisher
PERGAMON-ELSEVIER SCIENCE LTD
Issue Date
2013-07
Language
English
Article Type
Article
Keywords

AB-INITIO CALCULATIONS; SOLID-SOLUTION; MULTIPRINCIPAL ELEMENTS; SYSTEM; MICROSTRUCTURE; DECOMPOSITION; PHASE; DEFORMATION; WIRE

Citation

ACTA MATERIALIA, v.61, no.12, pp.4696 - 4706

ISSN
1359-6454
DOI
10.1016/j.actamat.2013.04.059
URI
http://hdl.handle.net/10203/207058
Appears in Collection
MS-Journal Papers(저널논문)
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