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Page 2 of 15 Ying et al. Microstructures 2023;3:2023018 https://dx.doi.org/10.20517/microstructures.2022.47

and 15 also exhibited a good tensile ductility of 19% and 14%, respectively. In situ synchrotron X-ray diffraction
results revealed an inhomogeneous deformation behavior, i.e., the soft FCC phase yielded prior to the hard
Cr B-type phase, which bore more stress in the initial stage of the plastic deformation. In the later stage of the
2
plastic deformation, the ductility of the sample was provided by the FCC phase, together with some contributions
from the Cr B-type phase.
2
Keywords: Network-structured high-entropy alloys, neutron and X-ray diffraction, mechanical properties, fluxing
method

INTRODUCTION
High-entropy alloys (HEAs) or multi-principal-element alloys are a new class of structural materials that
[1-3]
have attracted widespread attention since their first synthesis in 2004 . The development of HEAs
provided a new strategy for alloy design, leading to the discovery of new alloys with superior properties in a
[4,5]
wide range of loading conditions . By tuning the composition, various researchers have developed HEAs
[6-8]
with exceptional ductility and fracture toughness at temperatures down to 20 K , as well as strong and
ductile mechanical behavior from cryogenic temperatures to 1073 K , and excellent soft magnetic
[9]
[10]
properties with high strength and ductility . Moreover, the nanoscale structural design has been applied to
further increase the strength and ductility of HEAs by introducing nanoscale precipitation , compositional
[11]
[13]
[12]
modulation , or disordered grain boundaries . However, these heterogeneous nanostructures may be
unstable at elevated temperatures or difficult to fabricate in bulk sizes [14,15] , which limits their industrial
application. On the other hand, at a larger (i.e., sub-micron to micron) scale, the structure of the HEAs
could also significantly influence their mechanical properties, as in the case of lamellar structures or
[16]
[17]
equiaxed grains . These structures could be controlled by conventional thermal/mechanical treatments,
i.e., cold/hot rolling or annealing [18-20] . Thus, developing new structures at the sub-micron to micron scale by
engineering-friendly methods could be a promising way to accelerate the application of HEAs.
The fluxing technique is a widely used heat treatment method in metallurgy, in which the impurity and
metallic oxide contents of the molten alloy are reduced by immersing in molten oxides or salts to
[22]
[21]
improve its properties. This approach has been successfully applied to achieve a large undercooling of
different alloy melts, in order to alter the solidification kinetics [23,24] or even form bulk metallic glasses .
[21]
Novel microstructures could be formed when the melt is solidified at a deeply undercooled state by fluxing,
which is difficult to reach with other techniques. For example, using the B O fluxing treatment, Fe-C and
3
2
Fe-B-C alloys can be cast into an interconnected network morphology at the submicron to micron scale,
showing higher strength and plasticity than white cast iron with a typical eutectic structure .
[25]
In this work, the B O fluxing treatment was applied to fabricate high-entropy alloys with novel network-
2
3
like microstructures (N-HEAs) [26,27] . A high degree of undercooling (385 K) was achieved for
[(FeNiCo) Cr ] B (x = 12, 15, 17) N-HEAs with a diameter of ~13 mm. The morphology of the
0.15 100-x x
0.85
microstructures was inspected by scanning electron microscopy (SEM) and transmission electron
microscopy (TEM), and the phase composition was studied by energy-dispersive spectroscopy (EDS) and
neutron diffraction. The deformation mechanism was further investigated using in situ synchrotron X-ray
diffraction during tension test. We also discuss the origin of the large undercooling, the relationship of the
mechanical properties with the microstructures, as well as phase fractions, and the deformation mechanism.