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Zhou et al. J Mater Inf 2022;2:18 https://dx.doi.org/10.20517/jmi.2022.27 Page 11 of 21

Figure 11. (A) Engineering tensile stress-strain curves of as-printed FeCoNiAlTi compared with as-cast FeCoNi based alloy. (B) HRTEM
image showing multiple SFs. BF-STEM images of as-printed FeCoNiAlTi HEA after aging at 780 °C showing (C) high-density
dislocations network architectures and (D) sub-grain architectures consisting of L1 -type ordered multicomponent nanoprecipitate and
[89] 2
FCC disordered multicomponent matrix phase . SF: stacking faults; OMCNP: L1 -type ordered multicomponent nano-precipitate;
2
DOMCM: FCC disordered multicomponent matrix; HDDs: high-density dislocations.
high-density dislocation networks and coherent particles to the matrix using the L-PBF technique and
subsequent heat treatment. Similar methods have also been applied to other HEAs to improve their
mechanical properties and corrosion properties, including Co CrFeNi Ti Mo , FeCoNiAl Ti and
1.5
1.5
0.5
7
7
0.1
FeCoNiAl Ti [85-88] .
3 3
Strengthening and toughening mechanisms in AM of HEAs
The mechanical properties of HEAs from AM are usually superior to those of as-cast samples, which can be
attributed to the simultaneous activation of various strengthening mechanisms, including dislocation
strengthening, grain refining strengthening, solid solution strengthening, precipitation hardening and
twinning/transformation-induced plasticity (TWIP/TRIP).

Dislocation strengthening is widely recognized as one of the main reasons for the enhanced yield strength of
single-phase HEAs from AM. Due to the ultrafast cooling rate of L-PBF, a high-density nanosized cell
[59]
structure is formed within the as-printed FeCoCrNiMn HEA . In addition, the cell walls are decorated
with high-density dislocations [Figure 4B]. The cell walls act as obstacles to the dislocation motion, leading
[59]
to a significant increase in dislocation density within the cell walls. Zhu et al. calculated the contributions
[99]
of grain refinement and dislocation strengthening to the yield strength based on the following equation :