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Page 30 of 45 Mooraj et al. J Mater Inf 2023;3:4 https://dx.doi.org/10.20517/jmi.2022.41

throughput experimental methods are needed to characterize the manufactured materials’ properties to
experimentally verify which set of composition and processing conditions ultimately leads to the target
performance. This section focuses primarily on the different high-throughput methods which can rapidly
characterize important material properties such as hardness, strength, ductility, phase and composition,
magnetic hysteresis, saturation magnetization, and corrosion resistance.

Mechanical property characterization
Mechanical properties such as strength and ductility are crucial to assess the performance of a material for
[184]
structural applications . A few important criteria exist for a mechanical test considered to be useful for
[185]
screening HEAs. First, the sample size and microstructure must represent bulk-like conditions . Second,
the test should include a dominant tensile component, as real application conditions often include some
[185]
tensile stresses . Microhardness and nanoindentation tests are the most common approach towards high-
throughput screening of structural materials. These methods can quickly and accurately estimate bulk yield
[185]
strength . Nanoindentation can also offer broad insights into the post-yielding attributes through analysis
[186]
of the stress-strain curves it produces . The local nature of these two techniques also makes them highly
useful in graded materials libraries where many compositions and microstructures can be manufactured in
a single sample for rapid screening.

Here two example studies are provided that use microhardness testing to investigate the effect of
composition on hardness. Jiang et al. produced various compositions of CoFeNi VMo alloys to test the
[187] x y
effects of composition and microstructure on the hardness . This work concluded that an increase in the
Mo content led to increased precipitation of the CoMo Ni-type intermetallic phase. An increase in Ni
2
content increased the FCC solid solution phase and decreased the hardness. Figure 15A depicts the hardness
of the various compositions showing that the peak hardness was reached at the composition equiatomic
CoFeNiVMo. Pegues et al. also used micro-hardness indentation to build a hardness map of a graded Ta x
[166]
CoCrFeMnNi sample, as shown in Figure 15B . This map allowed them to rapidly determine the effect of
Ta addition on the hardness of this Cantor alloy-based system. Higher Ta contents encouraged the
formation of TaNi-rich intermetallic in the interdendritic region, which caused significant increases in
hardness.

Although micro-indentation methods can provide reasonable data for screening materials, the most reliable
method to investigate material properties is a lab-scale tension test with samples that conform to either the
ASTM E8 standard or another equivalent internationally recognized standard. Here the authors of this
review present one example from the literature and their own unpublished data to illustrate the typical
results that can be achieved in a combinatorial HEA library. Ma et al. added Nb to the AlCoCrFeNi system,
which led to the formation of Laves phase that increased the strength of the alloy while decreasing the
[188]
ductility . Tuning the Nb content allowed them to tune the compressive properties [Figure 15C]. This
result indicates that the addition of intermetallic forming elements can be used to achieve a wide array of
properties that can be optimized for application-specific uses. Following this design philosophy, the authors
of this review recently used DED to produce CoCrFeNiTi alloys to achieve a composition with improved
x
mechanical properties. The tensile stress-strain curves of our investigated CoCrFeNiTi HEAs are shown in
x
Figure 15D. These results show that adding Ti to the base quaternary alloy increases the yield strength while
decreasing the ductility until x = 0.2. Beyond this threshold, the yield strength and the ductility of the alloy
drop simultaneously. It has been well established that the introduction of Ti into the CoCrFeNi system leads
to the formation of brittle intermetallic phases that causes decreased ductility and increased hardness and
yield strength [189-191] . The drop in yield strength from x = 0.2 to x = 0.25 is likely a result of defects that
occurred during printing due to a higher fraction of brittle phases.