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PSFC/JA-20-33
Combinatorial development of the low-density high-entropy alloy Al10Cr20Mo20Nb20Ti20Zr10 having gigapascal strength at 1000 °C
Owais Ahmed Waseema1,2, Ho JinRyu1
1 Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, 291 Daehakro, Yuseong-gu, Daejeon, 34141, Republic of Korea 2 Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
March 2020
Plasma Science and Fusion Center Massachusetts Institute of Technology
Cambridge MA 02139 USA
This study is supported by NRF grant of MSIT (NRF-2015R1A2A2A01002436, NRF- 2020R1A5A6107701, NRF-2017K1A3A7A09016308), Republic of Korea, and by the Asian Office of Aerospace Research and Development (AOARD) through a grant FA2386-19-1-4009.
Submitted to Journal of Alloys and Compounds
1
Combinatorial development of the low-density high-entropy alloy
Al10Cr20Mo20Nb20Ti20Zr10 having gigapascal strength at 1000 ℃
Owais Ahmed Waseema, b, Ho Jin Ryua*
aDepartment of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and
Technology, 291 Daehakro, Yuseong-gu, Daejeon 34141, Republic of Korea
bPlasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139
*Corresponding Author: Tel.: +82–42–350–3812, Fax: +82–42–350–3810, E-mail address:
hojinryu@kaist.ac.kr (Ho Jin Ryu)
2
Abstract
A pseudo-ternary combinatorial approach to AlxTayVzCr20Mo20Nb20Ti20Zr10 revealed the
composition of refractory high-entropy alloys characterized by outstanding high-temperature
yield strength. Compression testing of Al10Cr20Mo20Nb20Ti20Zr10 disclosed yield strengths of
1206 MPa at 1000 ℃, one of the highest values reported for refractory high-entropy alloys. Ta-
containing AlxTayVzCr20Mo20Nb20Ti20Zr10 presented a lower high-temperature strength, while
characterization of Al10Cr20Mo20Nb20Ti20Zr10 showed C14 Al2Zr- and NbCr2-type hexagonal
Laves intermetallics, with a hardness of ~10.5 GPa (higher than that of the body centered cubic
phase, at ~9 GPa). The stronger bonds between Al and transition metals appear to give rise to
extraordinary load-bearing capabilities in Al10Cr20Mo20Nb20Ti20Zr10, at high temperatures.
Owing to this rare combination of relatively low density (6.96 g/cm3) and remarkable high-
temperature strength, Al10Cr20Mo20Nb20Ti20Zr10 has emerged as a potential material for high-
temperature structural applications.
Keywords
High-entropy alloy, refractory metals, combinatorial metallurgy, mechanical properties
3
1. Introduction
Refractory high-entropy alloys (HEAs, having 5–13 elements in 5–35 at.%) [1–3] are being
explored for possible applications in the aerospace, automobile, and power industries. Several
refractory HEAs with promising heat-resistant properties, including high strength levels (e.g.,
MoNbTaW (405 MPa at 1600 ℃) and MoNbTaVW (477 MPa at 1600 ℃) [4]), and oxidation
resistance (e.g., 0.5 mg/cm2 weight gain in AlCrMoNbTi after oxidation, for one h at 900 ℃, in
air [5,6]) have been reported.
Exchanging constituents and varying element concentrations significantly affect HEA properties
[7,8]. The replacement of Ta in HfNbTaTiZr, with Mo, to develop HfMoNbTiZr, improved its
room-temperature compressive strength from 1250 MPa to 1719 MPa [9], while adding Al to
AlxNbTaTiV led to a yield strength improvement from 1092 MPa (x = 0) to 1330 MPa (x = 0.25)
[10]. Composition modifications like these have led to the development of AlMo0.5NbTa0.5TiZr,
which has shown an impressive combination of high-temperature mechanical properties, that is,
a compressive yield strength of 745 MPa, and a fracture strain of > 50% (at 1000 ℃) [11].
Although several HEAs with promising properties have been reported, the achievement of
desirable properties remains somewhat unpredictable [12]. Studying combinatorial HEA libraries
containing ranges of elements—with the aim of discovering promising compositions with
improved properties for further development and commercialization—is therefore useful. In our
previous study, we undertook the combinatorial development of the novel HEAs
AlxCryMozNbTiZr (a, b, and c: 10–30 at.%), which revealed relatively good oxidation resistance,
as Al20Cr10Mo10Nb20Ti20Zr20 and Al30Cr10Nb20Ti20Zr20 (21 mg/cm2 and 20 mg/cm2 weight gains,
after 20 h of oxidation at 1000 ℃, respectively) [13], when compared to several other refractory
4
HEAs and conventional alloys. We focused on Al20Cr10Mo10Nb20Ti20Zr20, as the presence of Mo
in this HEA suggested it would exhibit good strength at high temperatures.
In this study, we locked in the base composition as Cr20Mo20Nb20Ti20Zr10, and decided to vary
the Al content, from 0 to 10 at.%, to achieve a balance between oxidation resistance and strength,
with a gradual increase/decrease of Ta and V, at the cost of 10 at.% Zr (so that oxidation
resistance could be improved [14]), considering their renown in HEA strengthening [4,15]. In
this way, we designed a pseudo-ternary combinatorial system of HEA, that is,
AlxTayVzCr20Mo20Nb20Ti20Zr10 (AlxTayVz-Q, where x + y + z = 10 at.%, and Q is the quinary
Cr20Mo20Nb20Ti20Zr10).
2. Experimental Procedures
Arc melting of 99.9% metal sources to develop AlxTayVz-Q HEA samples (Table I) was carried
out using an ACM-01 arc melting furnace (DAIA-VACUUM, Japan). Sample remelting (five
times) and further homogenization (at 1200 ℃ for 24 h, followed by air cooling) were carried out
to improve their chemical homogeneity. Microstructural examinations were carried out by X-ray
diffraction (XRD, D/MAX-2500, Rigaku, USA), scanning electron microscopy (SEM, FEI
Magellan 400, USA), and energy dispersive spectroscopy (EDS, coupled with SEM). The
contribution of each phase to the respective alloy’s mechanical properties was analyzed by
taking nano-indentation hardness measurements of each phase, using an iNano nano-indentor
(Nanomechanics, Inc., USA). Cylindrical samples, with dimensions of 6 mm × 3 mm and 8 mm
× 3 mm (length × diameter), were subjected to both room-temperature and high-temperature
(1000 ℃) compression tests, at a strain rate of 10-4 /s, using an Instron 5982 device.
5
TABLE I HEA sample names, compositions, and theoretical densities
Sample
Name HEA Compositions (at.%)
Density (g/cm3)
Theoretical Measured
Al x
Ta y
Vz-
Q
(Q =
Cr 2
0M
o20N
b20T
i 20Z
r 10)
V10-Q V10Cr20Mo20Nb20Ti20Zr10 7.32 7.31
Al10-Q Al10Cr20Mo20Nb20Ti20Zr10 6.96 6.93
Ta10-Q Ta10Cr20Mo20Nb20Ti20Zr10 8.42 8.40
AlxVz-Q
(y = 0)
Al2.5V7.5-Q Al2.5V7.5Cr20Mo20Nb20Ti20Zr10 7.22 7.19
Al5.0V5.0-Q Al5.0V5.0Cr20Mo20Nb20Ti20Zr10 7.13 7.12
Al7.5V2.5-Q Al7.5V2.5Cr20Mo20Nb20Ti20Zr10 7.05 7.01
AlxTay-Q
(z = 0)
Al7.5Ta2.5-Q Al7.5Ta2.5Cr20Mo20Nb20Ti20Zr10 7.32 7.29
Al5.0Ta5.0-Q Al5.0Ta5.0Cr20Mo20Nb20Ti20Zr10 7.69 7.68
Al2.5Ta7.5-Q Al2.5Ta7.5Cr20Mo20Nb20Ti20Zr10 8.06 8.06
TayVz-Q
(x = 0)
Ta7.5V2.5-Q Ta7.5V2.5Cr20Mo20Nb20Ti20Zr10 8.15 8.05
Ta5.0V5.0-Q Ta5.0V5.0Cr20Mo20Nb20Ti20Zr10 7.88 7.75
Ta2.5V7.5-Q Ta2.5V7.5Cr20Mo20Nb20Ti20Zr10 7.60 7.53
AlxTayVz-
Q
Al2.5Ta5.0V2.5-Q Al2.5Ta5.0V2.5Cr20Mo20Nb20Ti20Zr10 7.78 7.77
Al5.0Ta2.5V2.5-Q Al5.0Ta2.5V2.5Cr20Mo20Nb20Ti20Zr10 7.42 7.35
Al2.5Ta2.5V5.0-Q Al2.5Ta2.5V5.0Cr20Mo20Nb20Ti20Zr10 7.51 7.44
3. Results and discussion
The pseudo-ternary combinatorial library of post-homogenization microstructures, along with
three representative X-ray diffraction analyses, are shown in Fig. 1. The SEM micrographs show
a granular microstructure, with secondary phases in the intergranular region. Refractory HEAs
typically show various types of hexagonal (C14) and cubic (C15) Laves intermetallics [13]. XRD
analysis of homogenized AlxTayVz-X revealed a major body-centered cubic (BCC) phase, along
with secondary phases. The representative XRD patterns for homogenized AlxTayVz-Q are
shown in Fig. 1 (b)–(d).
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Fig. 1. (a) A pseudo-ternary combinatorial library of the microstructures of homogenized
AlxTayVzCr20Mo20Nb20Ti20Zr10; XRD analysis spectra for (b) Al10-Q, (c) Ta10-Q, and (d) V10-Q
Al10-Q, Ta10-Q, and V10-Q mainly show BCC phases, with 0.303, 0.303, and 0.319 nm lattice
parameters, respectively, (Table II). Al2Zr- and NbCr2-type C14 Laves were identified in Al10-Q,
7
while Cr2Zr-type C14 and Cr2Ta-type C15 Laves were observed in Ta10-Q, with V10-Q showing
(CrV)Zr-type C15 Laves. The volume% of the Laves phases in Al10-Q, Ta10-Q, and V10-Q, as
determined by image analysis, were 30 vol.%, 35 vol.%, and 22 vol.%, respectively. Laves phase
formation was observed in HEAs using Allen electronegativity differences (ΔXAllen), atomic size
differences (δr), and d-orbital energy levels (Md) exceeding 7%, 5%, and 0.915 eV, respectively
[16,17]. The occurrence of the Laves phase in HEAs is estimated by comparing ΔXAllen, δr, and
Md with these criteria, so using these methods, we calculated ΔXAllen, δr, and Md for AlxTayVz-Q,
and found them to be in the ranges of 7.38–7.74%, 6.35–6.62%, and 1.865–1.933 eV. These
values suggested the formation of Laves phases in AlxTayVz-Q.
TABLE II Analysis of solid solution and Laves phases in AlxTayVz-Q
HEA Phase
Structure,
Strukturbericht Designation,
Space Group
and JCPDS
Lattice Parameter
(nm)
Volume%
Atomic
Size Difference
(%)
Allen
Electronegativity Difference
(ΔXAllen, %)
d-orbital
energy level
(Md, eV)
Al10-Q
Solid solution BCC a = b = c = 0.303 70
6.35 7.66 1.900 Laves
intermetallics
Al2Zr, C14 hexagonal, p63/mmc (194)
[PDF#48-1384]
a = b = 0.5281,
c = 0.8743
30
NbCr2, C14, hexagonal, p63/mmc (194)
[PDF#47-1638]
a = b = 0.4976,
c = 0.8059
Ta10-Q
Solid solution BCC a = b = c = 0.323 65
6.38 7.74 1.933 Laves
intermetallics
Cr2Zr, C14, hexagonal,
p63/mmc (194)
[PDF#06-0613]
a = b = 0.5089,
c = 0.8279
35
Cr2Ta, C15, cubic,
Fd3m (227) [PDF#20-
0317]
a = b = c = 1.145
V10-Q
Solid solution BCC a = b = c = 0.319 78
6.62 7.38 1.865 Laves
intermetallics
(CrV)Zr, C15, cubic,
Fd3m (227) [01-071-
7632]
a = b = c = 0.733 22
8
Fig. 2. EDS mapping ((a), (d), (g)), point EDS analyses ((b), (e), (h)), and nano-indentation
hardness results, for the solid solution and Laves intermetallic phases ((c), (f), (i)) of V10-Q,
Ta10-Q, and Al10-Q, respectively
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EDS analysis results for the Laves phases observed in V10-Q, Al10-Q, and Ta10-Q are shown in
Fig. 2 (a), (d), and (g), respectively. In addition to the main constituents of Laves phases
identified by XRD, notable concentrations of other elements were also present in the Laves
intermetallics, suggesting the possible formation of high-entropy intermetallics, which could be a
promising area for future research [18].
The literature shows higher high-temperature mechanical properties for Laves phase
intermetallics than for BCC solid solutions [19]. The Laves phases maintain their strength at
elevated temperatures and enhance high-temperature strength in Laves-containing HEAs [20,21].
In order to confirm the role of the continuous network of Laves phase intermetallics, with regard
to the increased strength of Al10-Q, we carried out nano-indentation hardness tests on the
dendritic (BCC) and interdendritic (Laves intermetallics) regions of V10-Q, Al10-Q, and Ta10-Q.
These tests were repeated five times at different points in each region, and the average results are
shown in Fig. 2 (c), (f), and (i). High scattering in the nano-indentation hardness data was
observed near the surface, and the hardness decreased with increasing indentation depth. The
nano-indentation hardness data were processed using the Nix-Gao model, to extract the hardness
of the sample. The Nix-Gao model, expressed as shown in Eq. (i) showed a gradual decrease in
the measured hardness (H) up to the bulk hardness (H0), with increased indentation:
𝐻 = 𝐻0(1 +𝑑∗
𝑑)0.5 ----------------- (i)
The hardness at a critical depth (d*) is regarded as the representative or bulk-equivalent hardness
of the samples, with values listed in Table III.
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Table III. Estimated Vickers hardness of Al10-Q, V10-Q and Ta10-Q
HEA Phase
Bulk-equivalent hardness
(H, as GPa)
V10-Q
BCC 8.0
Laves 11.9
Al10-Q
BCC 9.0
Laves 10.5
Ta10-Q
BCC 8.4
Laves 11.0
Although nano-indentation data can have errors—because the stress field generated during
indentation is not limited to a single phase—it can be used for comparative analysis. The
comparison of the hardness values of the BCC and Laves phases clearly showed significantly
higher hardnesses for the Laves phases than those for BCC phases, which demonstrated the
significant contribution of the Laves phases to the mechanical behavior of AlxTayVz-Q.
This behavior, under a compressive load, is shown in Fig. 3. The interchange between 10 at.% V,
Al, and Ta did not impart any significant alteration of the room-temperature compressive yield
strength (Fig. 3 (a)), as V10-Q, Al10-Q, and Ta10-Q showed similar strengths—that is, 1572, 1692,
and 1626 MPa, respectively. It should be pointed out that the newly developed RHEAs show
brittleness at room temperature with the maximum compressive strain around 5%. However, as
there are some promising examples of ductile RHEAs showing tensile ductility at room
temperatures such as HfNbTiZr and HfNbTaTiZr [22][23][24], a further study for the
ductilization of the strong RHEA compositions should be necessary for their industrial
applications in the future.
The ductilization of the promising composition can be achieved by microstructural engineering.
There have been remarkable achievements for the ductilization of RHEAs to overcome the
11
conflict between high-temperature strength and room-temperature ductility. One such example
has been reported by Soni et al. [25]. The change in strength due to phase transformation is
inevitable, therefore the HEAs-based composites are also being exploited as reported in Mileiko
et al. [26]. Waseem et al. were able to achieve significant enhancement in the toughness of
W0.5TaTiVCr without sacrificing strength [27], which suggests that the extrinsic toughening can
potentially play an important role in the development of novel RHEAs with a good combination
of high-temperature strength and room-temperature ductility.
Fig. 3. Compressive stress–strain curves obtained at (a) room temperature, and (b) 1000 ℃
High-temperature strength is one of the most important characteristics of refractory HEAs;
therefore, compression tests for AlxTayVz-Q were also carried out at 1000 ℃, to assess the role of
Al, Ta, and V in imparting high strength in AlxTayVz-Q.
The results showed that Al10-Q exhibited a strength of ~ 1200 MPa, at 1000 ℃ (Fig. 3 (b)), while,
in contrast, V10-Q and Ta10-Q achieved values of ~ 830 MPa and ~ 500 MPa, respectively, under
the same conditions. Published HEA literature includes reports of improved high-temperature
strength due to the addition of Ta; for instance, HfMoNbTaTiZr and HfMoNbTiZr exhibited 814
MPa and 600/721 MPa strengths, respectively, at 1000 ℃ [22,23,24], although our study has
12
revealed rather different Ta behavior—that is, reduction in high temperature strength due to Ta
addition.
Fig. 4. Comparison of the high-temperature (1000 ℃) yield strengths and densities in refractory
HEAs
In order to compare the high-temperature yield strength and density of various HEAs, we
extracted data from the literature, as shown in Fig. 4 [4,6,15–31]. We divided these HEAs into
several groups, based on the degree of similarity between their compositions and ours. For
example, the group/region marked as AlCrNbTiV (Zr) represents the high-temperature
compressive strengths and densities of the HEAs AlCrNbTiV, AlCr0.5NbTiV, AlCrNbTiV,
AlCr1.5NbTiV, Al0.5CrNbTi2V0.5, Al0.25CrNbTiVZr, Al0.5CrNbTiVZr, and AlCrNbTiVZr, in
which Al, Cr, Nb, Ti, and V were present in every alloy, whereas Zr may or may not have been
present. The actual HEA compositions are also shown in the legend. The strength–density
regions of the various HEAs (as shown in Fig. 4) show the extent to which the strength and
13
density of certain HEAs can be varied by adding, removing, and/or changing the concentration(s)
of the elements shown in parentheses. Reported refractory HEAs with density levels < 7 g/cm3
showed relatively low high-temperature yield strength, which would hinder their high-
temperature structural applications. In contrast, some stronger HEAs showed high density levels,
and therefore would not suit the application to the automobile or aerospace industries, where
light alloys are needed.
The strength–density region of the AlxTayVz-Q HEA system can be seen to have covered a wide
range of high-strength values, while maintaining relatively low density, indicating that AlxTayVz-
Q provided the opportunity to design numerous new HEAs characterized by desirable
combinations of high-temperature strength and lower density levels. These data also highlighted
the outstanding high-temperature compressive strength of Al10-Q HEAs (higher than all other
refractory HEAs known thus far).
The mismatch between the atomic sizes of Al and the other Al10-Q constituents results in lattice
distortion—and so, consequently, the mechanical strength of Al10-Q increases. However, the
atomic size difference was relatively higher in the case of V10-Q (Table II), so that the mismatch
induced in Al10-Q by the atomic size of Al cannot have been the only reason for the promising
strength of Al10-Q.
In order to reveal the mechanism behind the strengthening brought about by the addition of Al in
refractory HEAs that incorporate transition metals and Al, Qui et al. performed density
functional theory (DFT) calculations [44]; these calculations revealed the hybridization of p and
s states from Al atoms, with d states from transition metals, which resulted in the formation of
strong, directionally angular bonds between the Al atoms and their neighbors in transition metals.
Such strong bonds were not detected between the constituents of Al-free refractory HEAs [44],
14
supporting the fact that the addition of V and Ta in Cr20Mo20Nb20Ti20Zr10—to form V10-Q and
Ta10-Q, respectively—did not result in a remarkably strong HEA. In addition to the hybridization
of the p and s states from Al atoms, the presence of Mo in AlxTayVz-Q also facilitated high
temperature strength, while Mo-free RHEAs, such as AlNbTiV(Zr) and/or AlCrNbTiV(Zr)
(Figure 4) showed remarkably low strength, at 1000 ℃.
We have carried out combinatorial synthesis and analysis of a refractory HEA (AlxTayVz-Q), and
explored a novel HEA, Al10Cr20Mo20Nb20Ti20Zr10, which exhibited gigapascal strength and low
density, at 1000 ℃, and showed that it possessed characteristics considered very desirable for the
application to the aerospace, automobile, and power industries. To understand this potential
better, additional research into high-temperature oxidation resistance is needed
15
4. Conclusions
In summary, combinatorial synthesis and analysis of AlxTayVzCr20Mo20Nb20Ti20Zr10 (x, y, and
z: 0–10 at.%) high-entropy alloys were carried out. Arc-melted samples were homogenized at
1200 ℃ for 24 h and air cooled. Considering the potential load-bearing applications of HEAs,
quasi-static compression tests were conducted, at room temperature and 1000 ℃, and analysis of
the compressive stress–strain curves revealed outstanding high-temperature strength, for
Al10Cr20Mo20Nb20Ti20Zr10 (Al10-Q) (1206 MPa), along with low density (6.96 g/cm3). Thorough
characterization of the Al10-Q microstructure, using XRD and EDS analyses, revealed Al2Zr- and
NbCr2-type hexagonal Laves. The BCC phase revealed a bulk equivalent hardness of 9 GPa,
while for Laves intermetallics, the result was 10.5 GPa. These promising mechanical
characteristics suggest that this low-density, ultra-strong HEA (Al10-Q) has very good potential
for future, high-temperature applications.
Declaration of Interest
None.
Author Contributions
Both authors contributed to the manuscript preparation. Owais Ahmed Waseem performed the
experiments and analyzed results under the direct supervision of Ho Jin Ryu. Both authors
reviewed the manuscript.
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Acknowledgments
This study is supported by NRF grant of MSIT (NRF-2015R1A2A2A01002436, NRF-
2020R1A5A6107701, NRF-2017K1A3A7A09016308), Republic of Korea, and by the Asian
Office of Aerospace Research and Development (AOARD) through a grant FA2386-19-1-4009.
References
[1] N.D. Stepanov, N.Y. Yurchenko, S.V. Zherebtsov, M.A. Tikhonovsky, G.A. Salishchev,
Aging behavior of the HfNbTaTiZr high entropy alloy, Mater. Lett. (2017).
doi:10.1016/j.matlet.2017.09.094.
[2] N. Yurchenko, N. Stepanov, M. Tikhonovsky, G. Salishchev, Phase Evolution of the
AlxNbTiVZr (x = 0; 0.5; 1; 1.5) High Entropy Alloys, Metals (Basel). 6 (2016) 298.
doi:10.3390/met6120298.
[3] B. Gwalani, R.M. Pohan, O. Ahmed, T. Alam, S. Hyung, H. Jin, R. Banerjee, Scripta
Materialia Strengthening of Al 0 . 3 CoCrFeMnNi-based ODS high entropy alloys with
incremental changes in the concentration of Y 2 O 3, Scr. Mater. 162 (2019) 477–481.
doi:10.1016/j.scriptamat.2018.12.021.
[4] N.N. Guo, L. Wang, L.S. Luo, X.Z. Li, R.R. Chen, Y.Q. Su, J.J. Guo, H.Z. Fu, Effect of
composing element on microstructure and mechanical properties in Mo-Nb-Hf-Zr-Ti
multi-principle component alloys, Intermetallics. 69 (2016) 13–20.
doi:10.1016/j.intermet.2015.10.011.
[5] B. Gorr, F. Mueller, H.J. Christ, T. Mueller, H. Chen, A. Kauffmann, M. Heilmaier, High
temperature oxidation behavior of an equimolar refractory metal-based alloy [Formula
17
presented] with and without Si addition, J. Alloys Compd. 688 (2016) 468–477.
doi:10.1016/j.jallcom.2016.07.219.
[6] H. Chen, A. Kauffmann, B. Gorr, D. Schliephake, C. Seemüller, J.N. Wagner, H.J. Christ,
M. Heilmaier, Microstructure and mechanical properties at elevated temperatures of a new
Al-containing refractory high-entropy alloy Nb-Mo-Cr-Ti-Al, J. Alloys Compd. 661 (2016)
206–215. doi:10.1016/j.jallcom.2015.11.050.
[7] B. Gwalani, V. Soni, O.A. Waseem, S.A. Mantri, R. Banerjee, Laser additive
manufacturing of compositionally graded AlCrFeMoVx (x = 0 to 1) high-entropy alloy
system, Opt. Laser Technol. 113 (2019) 330–337. doi:10.1016/j.optlastec.2019.01.009.
[8] O.A. Waseem, J. Lee, H.M. Lee, H.J. Ryu, The effect of Ti on the sintering and
mechanical properties of refractory high-entropy alloy TixWTaVCr fabricated via spark
plasma sintering for fusion plasma-facing materials, Mater. Chem. Phys. 210 (2018) 87–
94. doi:10.1016/j.matchemphys.2017.06.054.
[9] O.A. Waseem, H.J. Ryu, Powder Metallurgy Processing of a WxTaTiVCr High-Entropy
Alloy and Its Derivative Alloys for Fusion Material Applications, Sci. Rep. 7 (2017) 1926.
doi:10.1038/s41598-017-02168-3.
[10] X. Yang, Y. Zhang, P.K. Liaw, Microstructure and compressive properties of
NbTiVTaAlx high entropy alloys, Procedia Eng. 36 (2012) 292–298.
doi:10.1016/j.proeng.2012.03.043.
[11] O.N. Senkov, S. V. Senkova, C. Woodward, Effect of aluminum on the microstructure
and properties of two refractory high-entropy alloys, Acta Mater. 68 (2014) 214–228.
doi:10.1016/j.actamat.2014.01.029.
[12] D.B. Miracle, O.N. Senkov, A critical review of high entropy alloys and related concepts,
18
Acta Mater. 122 (2017) 448–511. doi:10.1016/j.actamat.2016.08.081.
[13] O.A. Waseem, U. Auyeskhan, H.M. Lee, H.J. Ryu, A combinatorial approach for the
synthesis and analysis of AlxCryMozNbTiZr high-entropy alloys: Oxidation behavior, J.
Mater. Res. (2018) 1–9. doi:10.1557/jmr.2018.241.
[14] E.M. Savitskii, G.S. Burkhanov, Physical Metallurgy of Refractory Metals and Alloys,
2012. doi:10.1007/978-1-4684-1572-8.
[15] N.N. Guo, L. Wang, L.S. Luo, X.Z. Li, R.R. Chen, Y.Q. Su, J.J. Guo, H.Z. Fu, Hot
deformation characteristics and dynamic recrystallization of the MoNbHfZrTi refractory
high-entropy alloy, Mater. Sci. Eng. A. 651 (2016) 698–707.
doi:10.1016/j.msea.2015.10.113.
[16] N. Yurchenko, N. Stepanov, G. Salishchev, Laves-phase formation criterion for high-
entropy alloys, Mater. Sci. Technol. (United Kingdom). 33 (2017) 17–22.
doi:10.1080/02670836.2016.1153277.
[17] Y. Lu, Y. Dong, L. Jiang, T. Wang, T. Li, Y. Zhang, A criterion for topological close-
packed phase formation in high entropy alloys, Entropy. 17 (2015) 2355–2366.
doi:10.3390/e17042355.
[18] T.P. Yadav, S. Mukhopadhyay, S.S. Mishra, N.K. Mukhopadhyay, O.N. Srivastava,
Synthesis of a single phase of high-entropy Laves intermetallics in the Ti–Zr–V–Cr–Ni
equiatomic alloy, Philos. Mag. Lett. 97 (2017) 494–503.
doi:10.1080/09500839.2017.1418539.
[19] N.Y. Yurchenko, N.D. Stepanov, D.G. Shaysultanov, M.A. Tikhonovsky, G.A. Salishchev,
Effect of Al content on structure and mechanical properties of the AlxCrNbTiVZr (x=0;
0.25; 0.5; 1) high-entropy alloys, Mater. Charact. 121 (2016) 125–134.
19
doi:10.1016/j.matchar.2016.09.039.
[20] N.D. Stepanov, N.Y. Yurchenko, D.V. Skibin, M.A. Tikhonovsky, G.A. Salishchev,
Structure and mechanical properties of the AlCrxNbTiV (x = 0, 0.5, 1, 1.5) high entropy
alloys, J. Alloys Compd. 652 (2015) 266–280. doi:10.1016/j.jallcom.2015.08.224.
[21] N.Y. Yurchenko, N.D. Stepanov, S. V. Zherebtsov, M.A. Tikhonovsky, G.A. Salishchev,
Structure and mechanical properties of B2 ordered refractory AlNbTiVZrx (x = 0–1.5)
high-entropy alloys, Mater. Sci. Eng. A. 704 (2017) 82–90.
doi:10.1016/j.msea.2017.08.019.
[22] O.N. Senkov, A.L. Pilchak, S.L. Semiatin, Effect of Cold Deformation and Annealing on
the Microstructure and Tensile Properties of a HfNbTaTiZr Refractory High Entropy
Alloy, Metall. Mater. Trans. A Phys. Metall. Mater. Sci. 49 (2018) 2876–2892.
doi:10.1007/s11661-018-4646-8.
[23] Y.D. Wu, Y.H. Cai, T. Wang, J.J. Si, J. Zhu, Y.D. Wang, X.D. Hui, A refractory
Hf25Nb25Ti25Zr25 high-entropy alloy with excellent structural stability and tensile
properties, Mater. Lett. 130 (2014) 277–280. doi:10.1016/j.matlet.2014.05.134.
[24] S. Sheikh, S. Shafeie, Q. Hu, J. Ahlström, C. Persson, J. Veselý, J. Zýka, U. Klement, S.
Guo, Alloy design for intrinsically ductile refractory high-entropy alloys, J. Appl. Phys.
120 (2016). doi:10.1063/1.4966659.
[25] V. Soni, O.N. Senkov, B. Gwalani, D.B. Miracle, R. Banerjee, Microstructural Design for
Improving Ductility of An Initially Brittle Refractory High Entropy Alloy, Sci. Rep. 8
(2018) 1–10. doi:10.1038/s41598-018-27144-3.
[26] S.T. Mileiko, S.A. Firstov, N.A. Novokhatskaya, V.F. Gorban, N.P. Krapivka, Oxide-
fibre/high-entropy-alloy-matrix composites, Compos. Part A Appl. Sci. Manuf. 76 (2015)
20
131–134. doi:10.1016/j.compositesa.2015.05.023.
[27] O.A. Waseem, H.J. Ryu, Toughening of a low-activation tungsten alloy using tungsten
short fibers and particles reinforcement for fusion plasma-facing applications, Nucl.
Fusion. 59 (2019). doi:10.1088/1741-4326/aaf43f.
[28] C.C. Juan, K.K. Tseng, W.L. Hsu, M.H. Tsai, C.W. Tsai, C.M. Lin, S.K. Chen, S.J. Lin,
J.W. Yeh, Solution strengthening of ductile refractory HfMoxNbTaTiZr high-entropy
alloys, Mater. Lett. 175 (2016) 284–287. doi:10.1016/j.matlet.2016.03.133.
[29] K.K. Tseng, C.C. Juan, S. Tso, H.C. Chen, C.W. Tsai, J.W. Yeh, Effects of Mo, Nb, Ta,
Ti, and Zr on mechanical properties of equiatomic Hf-Mo-Nb-Ta-Ti-Zr alloys, Entropy.
21 (2019) 1–14. doi:10.3390/e21010015.
[30] Y. Zhang, Y. Liu, Y. Li, X. Chen, H. Zhang, Microstructure and mechanical properties of
a refractory HfNbTiVSi0.5 high-entropy alloy composite, Mater. Lett. 174 (2016) 82–85.
doi:10.1016/j.matlet.2016.03.092.
[31] W. Zhang, P.K. Liaw, Y. Zhang, A novel low-activation VCrFeTaxWx (x = 0.1, 0.2, 0.3,
0.4, and 1) high-entropy alloys with excellent heat-softening resistance, Entropy. 20
(2018). doi:10.3390/e20120951.
[32] Z. Guo, A. Zhang, J. Han, J. Meng, Effect of Si additions on microstructure and
mechanical properties of refractory NbTaWMo high-entropy alloys, J. Mater. Sci. 54
(2019) 5844–5851. doi:10.1007/s10853-018-03280-z.
[33] Q. Li, H. Zhang, D. Li, Z. Chen, S. Huang, Z. Lu, H. Yan, WxNbMoTa Refractory High-
Entropy Alloys Fabricated by Laser Cladding Deposition, Materials (Basel). 12 (2019)
533. doi:10.3390/ma12030533.
[34] O.N. Senkov, G.B. Wilks, J.M. Scott, D.B. Miracle, Mechanical properties of
21
Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys,
Intermetallics. 19 (2011) 698–706. doi:10.1016/j.intermet.2011.01.004.
[35] W. Guo, B. Liu, Y. Liu, T. Li, A. Fu, Q. Fang, Y. Nie, Microstructures and mechanical
properties of ductile NbTaTiV refractory high entropy alloy prepared by powder
metallurgy, J. Alloys Compd. 776 (2019) 428–436. doi:10.1016/j.jallcom.2018.10.230.
[36] Y. Zhang, Y. Liu, Y. Li, X. Chen, H. Zhang, Microstructure and mechanical properties of
a refractory HfNbTiVSi0.5 high-entropy alloy composite, Mater. Lett. 174 (2016) 82–85.
doi:10.1016/j.matlet.2016.03.092.
[37] O.N. Senkov, J.K. Jensen, A.L. Pilchak, D.B. Miracle, H.L. Fraser, Compositional
variation effects on the microstructure and properties of a refractory high-entropy
superalloy AlMo0.5NbTa0.5TiZr, Mater. Des. 139 (2018) 498–511.
doi:10.1016/j.matdes.2017.11.033.
[38] O.N. Senkov, D. Isheim, D.N. Seidman, A.L. Pilchak, Development of a refractory high
entropy superalloy, Entropy. 18 (2016) 1–13. doi:10.3390/e18030102.
[39] N.D. Stepanov, N.Y. Yurchenko, E.S. Panina, M.A. Tikhonovsky, S. V. Zherebtsov,
Precipitation-strengthened refractory Al0.5CrNbTi2V0.5 high entropy alloy, Mater. Lett.
188 (2017) 162–164. doi:10.1016/j.matlet.2016.11.030.
[40] N.D. Stepanov, N.Y. Yurchenko, V.S. Sokolovsky, M.A. Tikhonovsky, G.A. Salishchev,
An AlNbTiVZr0.5 high-entropy alloy combining high specific strength and good ductility,
Mater. Lett. 161 (2015) 136–139. doi:10.1016/j.matlet.2015.08.099.
[41] N.D. Stepanov, D.G. Shaysultanov, G.A. Salishchev, M.A. Tikhonovsky, Structure and
mechanical properties of a light-weight AlNbTiV high entropy alloy, Mater. Lett. 142
(2015) 153–155. doi:10.1016/j.matlet.2014.11.162.
22
[42] P.K. Liaw, G. Li, D. Liu, P. Yu, R. Liu, High-temperature high-entropy alloys Al x Co 15
Cr 15 Ni 70-x based on the Al-Ni binary system, Mater. Sci. Eng. A. 724 (2018) 283–288.
doi:10.1016/j.msea.2018.03.058.
[43] V. Bolbut, E. Wessel, M. Krüger, Phase stability and temperature-dependent compressive
strength of a low-density Fe32.3Al29.3Cu11.7Ni10.8Ti15.9 alloy, Scr. Mater. 150 (2018)
54–56. doi:10.1016/j.scriptamat.2018.02.042.
[44] S. Qiu, N. Miao, J. Zhou, Z. Guo, Z. Sun, Strengthening mechanism of aluminum on
elastic properties of NbVTiZr high-entropy alloys, Intermetallics. 92 (2018) 7–14.
doi:10.1016/j.intermet.2017.09.003.
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