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Zhou et al. J Mater Inf 2022;2:18 https://dx.doi.org/10.20517/jmi.2022.27 Page 7 of 21

Figure 6. Microstructure and defects of refractory HEAs fabricated by L-PBF: (A) NbMoTa; (B) NbMoTaTi; (C) NbMoTaTi Ni . (D)
[67]
0.5
0.5
Compressive strength of as-printed NbMoTaTi Ni at various temperatures .
0.5 0.5
BCC HEAs, mostly referred to as refractory HEAs, contain refractory elements, such as V, Nb, Mo, Ta, W,
Ti, Hf, and so on. Due to their sluggish diffusion rates and severe lattice distortion, refractory HEAs exhibit
[90]
excellent high-temperature mechanical properties . Therefore, compared with single-phase FCC HEAs,
these BCC-type refractory HEAs are considered as “the next generation of high-temperature
materials,”showing a wide range of application prospects. Unfortunately, the poor workability and high cost
of the raw materials make them difficult to be used at large scales. For example, Zhang et al. found that a
NbMoTa refractory HEA fabricated by L-PBF suffers from serious grain boundary cracking due to excessive
[67]
internal stress during the cooling process . As shown in Figure 6, adding Ni and Ti to the NbMoTa
refractory HEA can help to suppress the crack formation and enhance its formability and high-temperature
[67]
performance [Figure 6D] . The reason is mainly attributed to the formation of many extended dislocations
in the grain boundary phase, which transforms the crack defects into point defects and consequently
strengthens the grain boundaries. Nevertheless, limited work has been reported on the tensile properties of
the refractory HEAs manufactured by L-PBF.

AM of EHEAs
As discussed above, the comprehensive properties of as-printed single-phase HEAs cannot always meet the
actual requirements of the components, especially at elevated temperatures. For instance, as-printed single
FCC HEAs possess excellent ductility at both room and elevated temperatures but suffer from low strength.
Conversely, although refractory HEAs exhibit excellent strength at room and elevated temperatures, their
ductility is greatly sacrificed. As a result, to achieve a good balance between the strength and ductility of
HEAs, many researchers are now working on AM-EHEAs containing both FCC and BCC phases. The
processibility, microstructure and mechanical properties of EHEAs fabricated through AM methods have
been widely studied [68,69,74,91] . Guo et al. illustrated that as-printed AlCoCrFeNi HEAs exhibited a
2.1 [74]
completely eutectic structure consisting of ultrafine FCC and ordered B2 phases . The eutectic
microstructure changed from a lamellar structure to a cellular structure with a decreased laser energy input,
resulting in discrete tensile properties. Su et al. found that with increasing Al content in Al CrCuFeNi
x 2