In the past decade, the concept of high-entropy alloys (HEAs) or multi-principal element alloys (MPEAs), which are composed of at least four principal elements, significantly expands the compositional space for alloy design. This concept can also be employed in the design of superelastic alloys to promote the development of this functional material field. Here, we report the orientation-dependent superelasticity of a metastable Fe-27.5Ni-16.5Co-10Al-2.2Ta-0.04B (at.%) HEA through in situ micropillar compression tests along ⟨001⟩, ⟨011⟩, and ⟨111⟩ orientations. Our results show that considerable superelastic strains can be achieved along the three orientations in the metastable HEA via a reversible martensitic transformation. Thermoelastic martensite with thin-plate morphology was observed under cryogenic conditions. This work demonstrates that the maximum superelastic strains vary with different orientations, and the ⟨001⟩-oriented specimen shows the largest superelastic strain. The superelastic strains along specific orientations are compared with theoretical values calculated from the lattice deformation method and the energy minimization theory, respectively. The limited number of martensite variants under compression testing may be responsible for the discrepancy that exists in the experimental and the two theoretically predicted transformation strains. This study may provide a feasible strategy for the design of superelastic HEAs with specific orientation for applications in microsystems.

1.
E. P.
George
,
D.
Raabe
, and
R. O.
Ritchie
, “
High-entropy alloys
,”
Nat. Rev. Mater.
4
,
515
534
(
2019
).
2.
E. P.
George
,
W. A.
Curtin
, and
C. C.
Tasan
, “
High entropy alloys: A focused review of mechanical properties and deformation mechanisms
,”
Acta Mater.
188
,
435
474
(
2020
).
3.
Y.
Zhang
,
T.
Zuo
,
Z.
Tang
 et al., “
Microstructures and properties of high-entropy alloys
,”
Prog. Mater. Sci.
61
,
1
93
(
2014
).
4.
B.
Gludovatz
,
A.
Hohenwarter
,
D.
Catoor
 et al., “
A fracture-resistant high-entropy alloy for cryogenic applications
,”
Science
345
,
1153
1158
(
2014
).
5.
T.
Yang
,
Y.
Zhao
,
Y.
Tong
 et al., “
Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys
,”
Science
362
,
933
937
(
2018
).
6.
Z.
Fu
,
L.
Jiang
,
J.
Wardini
 et al., “
A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength
,”
Sci. Adv.
4
,
eaat8712
(
2018
).
7.
O. N.
Senkov
,
D. B.
Miracle
,
K. J.
Chaput
, and
J.-P.
Couzinie
, “
Development and exploration of refractory high entropy alloys—A review
,”
J. Mater. Res.
33
,
3092
3128
(
2018
).
8.
O. N.
Senkov
,
G. B.
Wilks
,
D. B.
Miracle
,
C. P.
Chuang
, and
P. K.
Liaw
, “
Refractory high-entropy alloys
,”
Intermetallics
18
,
1758
1765
(
2010
).
9.
Z.
Li
,
K. G.
Pradeep
,
Y.
Deng
,
D.
Raabe
, and
C. C.
Tasan
, “
Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off
,”
Nature
534
,
227
(
2016
).
10.
C.
Zhang
,
C.
Zhu
,
P.
Cao
 et al., “
Aged metastable high-entropy alloys with heterogeneous lamella structure for superior strength-ductility synergy
,”
Acta Mater.
199
,
602
612
(
2020
).
11.
S.
Wei
,
F.
He
, and
C. C.
Tasan
, “
Metastability in high-entropy alloys: A review
,”
J. Mater. Res.
33
,
2924
2937
(
2018
).
12.
S.
Li
,
D.
Cong
,
Z.
Chen
 et al., “
A high-entropy high-temperature shape memory alloy with large and complete superelastic recovery
,”
Mater. Res. Lett.
9
,
263
269
(
2021
).
13.
C.-H.
Chen
and
Y.-J.
Chen
, “
Shape memory characteristics of (TiZrHf) 50Ni25Co10Cu15 high entropy shape memory alloy
,”
Scr. Mater.
162
,
185
189
(
2019
).
14.
S.
Li
,
D.
Cong
,
X.
Sun
 et al., “
Wide-temperature-range perfect superelasticity and giant elastocaloric effect in a high entropy alloy
,”
Mater. Res. Lett.
7
,
482
489
(
2019
).
15.
D.
Canadinc
,
W.
Trehern
,
J.
Ma
 et al., “
Ultra-high temperature multi-component shape memory alloys
,”
Scr. Mater.
158
,
83
87
(
2019
).
16.
D.
Li
,
C.
Li
,
T.
Feng
 et al., “
High-entropy Al0. 3CoCrFeNi alloy fibers with high tensile strength and ductility at ambient and cryogenic temperatures
,”
Acta Mater.
123
,
285
294
(
2017
).
17.
C.
Zhang
,
C.
Zhu
,
T.
Harrington
, and
K.
Vecchio
, “
Design of non-equiatomic high entropy alloys with heterogeneous lamella structure towards strength-ductility synergy
,”
Scr. Mater.
154
,
78
82
(
2018
).
18.
C.
Zhang
,
C.
Zhu
, and
K.
Vecchio
, “
Non-equiatomic FeNiCoAl-based high entropy alloys with multiscale heterogeneous lamella structure for strength and ductility
,”
Mater. Sci. Eng. A
743
,
361
371
(
2019
).
19.
C.
Zhang
,
C.
Zhu
,
T.
Harrington
 et al., “
Multifunctional non-equiatomic high entropy alloys with superelastic, high damping, and excellent cryogenic properties
,”
Adv. Eng. Mater.
21
,
1800941
(
2019
).
20.
L. W.
Tseng
,
J.
Ma
,
S. J.
Wang
,
I.
Karaman
, and
Y. I.
Chumlyakov
, “
Effects of crystallographic orientation on the superelastic response of FeMnAlNi single crystals
,”
Scr. Mater.
116
,
147
151
(
2016
).
21.
L. W.
Tseng
,
J.
Ma
,
Y. I.
Chumlyakov
, and
I.
Karaman
, “
Orientation dependence of superelasticity in FeMnAlNi single crystals under compression
,”
Scr. Mater.
166
,
48
52
(
2019
).
22.
K.
Otsuka
and
C. M.
Wayman
,
Shape Memory Materials
(
Cambridge University Press
,
1999
).
23.
J. M.
Ball
and
R. D.
James
, “
Fine phase mixtures as minimizers of energy
,” in
Analysis and Continuum Mechanics
(
Springer
,
1989
), pp.
647
686
.
24.
H.
Sehitoglu
,
X.
Zhang
,
T.
Kotil
 et al., “
Shape memory behavior of FeNiCoTi single and polycrystals
,”
Metall. Mater. Trans. A
33
,
3661
3672
(
2002
).
25.
Y.
Yang
,
T.
Chen
,
L.
Tan
 et al., “
Bifunctional nanoprecipitates strengthen and ductilize a medium-entropy alloy
,”
Nature
595
,
245
249
(
2021
).
26.
P.
Krooß
,
C.
Somsen
,
T.
Niendorf
 et al., “
Cyclic degradation mechanisms in aged FeNiCoAlTa shape memory single crystals
,”
Acta Mater.
79
,
126
137
(
2014
).
27.
J.
Ma
,
B.
Kockar
,
A.
Evirgen
 et al., “
Shape memory behavior and tension–compression asymmetry of a FeNiCoAlTa single-crystalline shape memory alloy
,”
Acta Mater.
60
,
2186
2195
(
2012
).
28.
J.
Ma
,
B.
Hornbuckle
,
I.
Karaman
 et al., “
The effect of nanoprecipitates on the superelastic properties of FeNiCoAlTa shape memory alloy single crystals
,”
Acta Mater.
61
,
3445
3455
(
2013
).
29.
Y.
Song
,
X.
Chen
,
V.
Dabade
,
T. W.
Shield
, and
R. D.
James
, “
Enhanced reversibility and unusual microstructure of a phase-transforming material
,”
Nature
502
,
85
(
2013
).
30.
H.
Chen
,
Y.
Wang
,
Z.
Nie
 et al., “
Unprecedented non-hysteretic superelasticity of [001]-oriented NiCoFeGa single crystals
,”
Nat. Mater.
19
,
712
718
(
2020
).

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