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Page 6 of 21 Zhou et al. J Mater Inf 2022;2:18 https://dx.doi.org/10.20517/jmi.2022.27

Figure 4. Hierarchical microstructure and tensile properties of FeCoCrNiMn HEA fabricated by L-PBF: (A) inverse pole figure mapping of
as-printed sample along the building direction; (B) bright-field scanning transmission electron microscopy (BF-STEM) image of cellular
structure with corresponding SAED pattern; (C) engineering stress-strain curves of as-printed and as-cast samples (“V2000” and
[59]
“V2500” represent the scanning speed of the laser with values of 2000 and 2500 mm/s, respectively) .

Figure 5. Microstructure and tensile properties of as-printed FeCoCrNi HEA: (A) TEM image of FeCoCrNi HEA fabricated by L-PBF
[63]
showing high-density dislocation networks; (B) strain-stress curves of L-PBF-HEAs at different temperatures .

microstructures and mechanical properties of as-printed FCC HEAs have been widely studied. Zhu et al.
[59]
illustrated that a high relative density of 99.2% can be obtained by adopting suitable L-PBF parameters . In
addition, due to the ultrafast cooling rate and layer-by-layer manufacturing method of the L-PBF process,
the FeCoCrNiMn HEA showed hierarchical microstructure and excellent tensile properties. As illustrated in
Figure 4A, coarse columnar grains were formed along the building direction, while some fine cellular
structures can be observed within the columnar grains [Figure 4B]. Benefiting from the hierarchical
microstructure, the as-printed HEA showed superior tensile strength to the as-cast one [Figure 4C].

However, the strengths of the as-printed FCC HEAs are still insufficient and cannot satisfy some industrial
applications under extreme conditions, such as structural applications at elevated temperatures. Lin et al.
evaluated the tensile properties of FeCoCrNi HEA fabricated by L-PBF at room and elevated
[63]
temperatures . As shown in Figure 5, the as-printed FeCoCrNi HEA showed high-density dislocation
networks, leading to relatively high tensile properties at room temperature. Some dislocations obtained
sufficient activation energy at elevated temperatures to overcome the energy barrier binding them to the
networks. Therefore, the dislocation networks failed to provide sufficient resistance to dislocation
movement, thereby leading to a significant decrease in strength.