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Page 2 of 19 Chen et al. J Mater Inf 2023;3:10 https://dx.doi.org/10.20517/jmi.2023.06

[3]
“eutectic” was coined by Guthrie in 1884 to refer to easy melt (i.e., the minima on a liquidus curve) . Since
the melting temperature of a eutectic alloy is always lower than those of its constituent phases, eutectic
alloys often exhibit good castability. Additionally, their eutectic microstructures can be readily tailored
[4-6]
through thermomechanical processing for optimized properties, such as high rupture strength , good
[7-9]
high-temperature creep resistance , high thermal conductivity [10,11] and superior wear and corrosion
[12-15]
resistance . Compared to single-phase alloys, eutectic alloys usually possess balanced mechanical
[1,16-18]
properties that can meet demanding requirements in structural applications .
To date, a number of eutectic alloy systems have already been developed for various applications, such as
Sn-Pb as solder joints [19-21] , Sn-Ag for electronics [22-24] , Ni-Si for magnetics [25,26] , In-Ga for optics [27,28] and
[29,30]
Ni-Al-Cr for aerospace engineering . However, just like many other conventional alloys, the design of
conventional eutectic alloys is usually based on one principal element. If the phase diagram is not available,
alloying elements are then added in a trial-and-error manner to pinpoint a eutectic composition. While
people have been following such a design strategy for decades, this approach is costly, time-consuming, and
inefficient, particularly when it comes to compositionally complex alloys (CCAs), such as multi-principal-
[31-33] [34,35]
element alloys (MPEAs) and high entropy alloys (HEAs) , for which there is no phase diagram and
the associated compositional space is too broad to navigate with the traditional design strategy.

In the past, the development of HEAs in their infancy was mainly focused on the formation of single-phase
solid solutions [36-41] , while the recent trend has shifted to multi-phase HEAs with balanced mechanical
[42-44]
properties . One good example is the so-called eutectic high entropy alloys (EHEAs) comprising a
biphasic or triphasic microstructure with a lamellar or rod morphology [1,45] . By carefully controlling the
thermal and mechanical processing, EHEAs can exhibit a wide range of microstructural feature sizes,
ranging from tens of nanometers to a few microns [46-49] . Owing to these heterogeneous eutectic micro- or
nanostructures, EHEAs can attain high strength and good ductility [46,47,50,51] , remarkable creep resistance [45,52] ,
[53-55] [56]
superior thermal stability at elevated temperatures and good processability .

Given the vast hyper-dimensional compositional space for EHEAs, the traditional design strategy becomes
impractical. Therefore, several design methods were proposed recently to quickly locate the possible eutectic
or near-eutectic composition in the compositional space. These include, the simple mixing method [57-60] , the
[61-63] [64-67] [68]
grouping method , the pseudo-binary methods and the so-called “LEGO” method . The pros and
cons of these methods are listed in Table 1 and they can be categorized into two strategies, as summarized in
Figure 1. However, we note that these methods are mostly empirical; therefore, the related experimental
workload that one has to pay is heavy to verify these empirical predictions as the number of constituent
elements increases. To improve efficiency, people usually turned to machine learning (ML) as an alternative
[69,70]
to the traditional design strategy for the development of advanced alloys (i.e., titanium alloys , copper
[71,72] [73-75] [76-78]
alloys , shape memory alloys and even metallic glasses ). Recently, these efforts were extended to
[79-81]
the design of EHEAs . In the present work, we provide a critical overview of these recent efforts for the
development of EHEAs covering the empirical design methods and the data-driven methods.

EMPIRICAL DESIGN METHODS OF EUTECTIC HIGH ENTROPY ALLOYS
Linear combination of binary eutectics
Without a phase diagram, it is non-trivial and difficult to locate the eutectic compositions for multi-
component alloys and HEAs. Therefore, to facilitate the design of EHEAs, one strategy is to resort to the
[57,59,60,68]
phase diagrams of binary eutectics, which can be easily found in the literature . In other words, there
is a hypothesis that the eutectic microstructures of multi-component systems may inherit from some
[68,82,83]
binary/ternary eutectics . While this hypothesis remains to be verified theoretically, it indeed provides