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Mooraj et al. J Mater Inf 2023;3:4 https://dx.doi.org/10.20517/jmi.2022.41 Page 25 of 45

Figure 11. (A) Schematic illustration of high-throughput manufacturing of HEAs in a graded material under laser-directed
energy deposition (L-DED). This figure is quoted with permission from Pegues et al. [166] , copyright 2021, Elsevier; (B) schematic
illustration of manufacturing a graded material under laser powder bed fusion (L-PBF) conditions. This figure is quoted with
permission from Wen et al. [167] , copyright 2021, Elsevier; (C) graded material library produced via L-DED in Al CoCrFeNi. The graded
x
HEA library is remelted to investigate the effects of composition and cooling rate. This figure is quoted with permission from Li
et al. [171] , copyright 2020, Elsevier. HEA: High-entropy alloy.
[172]
Teh et al. used DED to produce compositionally graded pillars within the Co-Fe-Ni alloy system . By
adjusting the content of each element along the build direction, the phase fraction of FCC vs. BCC was
varied from pure BCC at the base of the pillar to dual phase FCC + BCC to pure FCC at the top. The
hardness also varied with build height due to changes in composition and grain size caused by increasing
the Ni concentration. They characterized the functional properties of each composition in addition to the
mechanical properties by measuring the saturation magnetization, coercivity, and electrical resistivity. After
analyzing the combination of properties, the authors presented a radar chart comparing some promising
compositions to pure Fe, as shown in Figure 12A.

[173]
Gwalani et al. varied the V content in an AlMoCrFeV (from x = 0 to x = 1) HEA system [Figure 12B] .
x
The addition of V led to solid solution hardening, increasing the hardness monotonically from 485 HV at
x = 0 to 581 HV at x = 1. The microstructure remained purely BCC for all compositions and remained stable
after annealing at 1,100 °C for 30 min. The grain size was also negligibly changed, which indicated high
[174]
thermal stability. Zhao et al. blended Ti and CoCrFeNi powders in various compositions . They then
layered the different compositions within a powder supply bin to build a compositionally graded pillar by
[174]
increasing the Ti content along the build direction . All compositions showed an FCC structure primarily
with minor BCC, Laves, and phases that contain Ti. Figure 12C shows a hardness map based on the results
taken from the printed graded structure. As the secondary phase volume fractions increased, the hardness
increased, and analysis of the various strengthening mechanisms suggested that the inclusion of the
secondary phases was the main cause of the increase in strength. However, high Ti content layers also
showed significant cracking. Thus, the authors concluded that 10 at. % was the maximum threshold of Ti
content to produce crack-free samples and parts in CoCrFeNiTix HEA system.