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Ying et al. Microstructures 2023;3:2023018 https://dx.doi.org/10.20517/microstructures.2022.47 Page 11 of 15

Table 3. ΔH values (kJ/mol) between elements calculated by Miedema’s model [58]
Elements Fe Ni Co Cr B
Fe / -2 -1 -1 -26
Ni -2 / 0 -7 -24
Co -1 0 / -4 -24
Cr -1 -7 -4 / -31
B -26 -24 -24 -31 /

Figure 7. Fracture surface of B12 (A and B) and B15 (C and D) tensile samples, displayed at different magnifications.

the crack activation. Similar to this phenomenon, the enhanced combination of strength and ductility in the
B12 alloy can be correlated to the dual-phase structure, where the hard Cr B-type intermetallic phase and
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the soft FCC phase deform synergically.

Figure 7 shows SEM images of the fracture surface of B12 obtained after the tensile test (the fracture surface
of the B15 sample, i.e., Figure 7C and D, is similar). As shown in Figure 7A, the fracture surface contained
uniformly distributed dimples, a typical fracture morphology for ductile samples . The size of the dimples
[62]
was about 3-5 μm, similar to the wavelength of a network structure. Furthermore, no large micro-voids were
found on the fracture surfaces. Previous studies showed that 304 L austenitic stainless steels and
[63]
CrFeCoNi HEAs with small-size dimples had high ductility. Our results indicate that the soft FCC phase
[62]
may participate in the deformation process in stages involving large plastic deformations, contributing to
improved ductility. The enlarged view of the fracture surface [Figure 7B] also displays some fracture
patterns with sharp angles (marked by yellow lines), similar to the intergranular fracture surface of brittle
samples . This may be attributed to the deformation of the Cr B-type phase.
[64]
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CONCLUSION
In this work, a series of [(FeNiCo) Cr ] B (x = 12, 15, 17) N-HEAs combining high strength and
0.15 100-x x
0.85
plasticity were successfully synthesized by the B O fluxing technique. We used a set of advanced
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