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Spherical nanoindentation creep behavior of nanocrystalline and coarse-grained CoCrFeMnNi high-entropy alloys

Spherical nanoindentation creep behavior of nanocrystalline and coarse-grained CoCrFeMnNi high-entropy alloys
Spherical nanoindentation creep behavior of nanocrystalline and coarse-grained CoCrFeMnNi high-entropy alloys
Time-dependent plastic deformation behavior of nanocrystalline (nc) and coarse-grained (cg) CoCrFeMnNi high-entropy alloys (HEAs) was systematically explored through a series of spherical nanoindentation creep experiments. High-pressure torsion (HPT) processing was performed for achieving nc microstructure in the HEA, leading to a reduction in grain size from ?46 ?m for the as-cast state to ? 33 nm at the edge of the HPT disk after 2 turns. Indentation creep tests revealed that creep deformation indeed occurs in both cg and nc HEAs even at room temperature and it is more pronounced with an increase in strain. The creep stress exponent, n, was estimated as ?3 for cg HEA and ?1 for nc HEA and the predominant creep mechanisms were investigated in terms of the values of n and the activation volumes. Through theoretical calculations and comparison of the creep strain rates for nc HEA and a conventional face-centered-cubic nc metal (Ni), the influence of sluggish diffusion on the creep resistance of nc HEA was analyzed. In addition, sharp indentation creep tests were performed for comparison purposes and the results confirmed that the use of a spherical indenter is clearly more appropriate for investigating the creep behavior of this HEA.
creep, high-entropy alloy. high-pressure torsion, nanocrystalline metal
1359-6454
314-322
Lee, D.H.
e46af0e0-234b-4e1a-81e0-36483fca6428
Seok, M.Y.
7cdc78d1-31c1-4037-a09b-c6d0a4954a4b
Zhao, Y.
d6302903-ff65-45d3-b16b-ccab58d5d835
Choi, I.C.
c53e67bf-ee34-4303-94ad-d9cddbaa28b4
He, J.
4e574b72-f610-4522-8df2-41be455328cc
Lu, Z.
e92770ea-27bf-4223-9b37-5a545e956a04
Suh, J.Y.
85a90e01-f462-40ec-8c81-5f2c5e441733
Langdon, T.G.
86e69b4f-e16d-4830-bf8a-5a9c11f0de86
Lee, D.H.
e46af0e0-234b-4e1a-81e0-36483fca6428
Seok, M.Y.
7cdc78d1-31c1-4037-a09b-c6d0a4954a4b
Zhao, Y.
d6302903-ff65-45d3-b16b-ccab58d5d835
Choi, I.C.
c53e67bf-ee34-4303-94ad-d9cddbaa28b4
He, J.
4e574b72-f610-4522-8df2-41be455328cc
Lu, Z.
e92770ea-27bf-4223-9b37-5a545e956a04
Suh, J.Y.
85a90e01-f462-40ec-8c81-5f2c5e441733
Langdon, T.G.
86e69b4f-e16d-4830-bf8a-5a9c11f0de86

Lee, D.H., Seok, M.Y., Zhao, Y., Choi, I.C., He, J., Lu, Z., Suh, J.Y. and Langdon, T.G. (2016) Spherical nanoindentation creep behavior of nanocrystalline and coarse-grained CoCrFeMnNi high-entropy alloys. Acta Materialia, 109, 314-322. (doi:10.1016/j.actamat.2016.02.049).

Record type: Article

Abstract

Time-dependent plastic deformation behavior of nanocrystalline (nc) and coarse-grained (cg) CoCrFeMnNi high-entropy alloys (HEAs) was systematically explored through a series of spherical nanoindentation creep experiments. High-pressure torsion (HPT) processing was performed for achieving nc microstructure in the HEA, leading to a reduction in grain size from ?46 ?m for the as-cast state to ? 33 nm at the edge of the HPT disk after 2 turns. Indentation creep tests revealed that creep deformation indeed occurs in both cg and nc HEAs even at room temperature and it is more pronounced with an increase in strain. The creep stress exponent, n, was estimated as ?3 for cg HEA and ?1 for nc HEA and the predominant creep mechanisms were investigated in terms of the values of n and the activation volumes. Through theoretical calculations and comparison of the creep strain rates for nc HEA and a conventional face-centered-cubic nc metal (Ni), the influence of sluggish diffusion on the creep resistance of nc HEA was analyzed. In addition, sharp indentation creep tests were performed for comparison purposes and the results confirmed that the use of a spherical indenter is clearly more appropriate for investigating the creep behavior of this HEA.

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Accepted/In Press date: 19 February 2016
e-pub ahead of print date: 11 March 2016
Published date: May 2016
Keywords: creep, high-entropy alloy. high-pressure torsion, nanocrystalline metal
Organisations: Engineering Mats & Surface Engineerg Gp, Engineering Science Unit, Faculty of Engineering and the Environment

Identifiers

Local EPrints ID: 389730
URI: http://eprints.soton.ac.uk/id/eprint/389730
ISSN: 1359-6454
PURE UUID: 210284ea-5694-467f-a5dc-7a93d5f7b083
ORCID for T.G. Langdon: ORCID iD orcid.org/0000-0003-3541-9250

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Date deposited: 14 Mar 2016 12:00
Last modified: 17 Dec 2019 01:50

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Contributors

Author: D.H. Lee
Author: M.Y. Seok
Author: Y. Zhao
Author: I.C. Choi
Author: J. He
Author: Z. Lu
Author: J.Y. Suh
Author: T.G. Langdon ORCID iD

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