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Mooraj et al. J Mater Inf 2023;3:4 https://dx.doi.org/10.20517/jmi.2022.41 Page 35 of 45

[205,206]
to be tested simultaneously . Rapid characterization via wire resistance to indicate a reduction in the
[207]
cross-sectional area has shown great potential to accelerate the analysis of corrosion resistance .
Additionally, optical characterization of the color change of a corroded substance can be correlated well
with traditional polarization curves. It can thus provide an easy screening method without the need for in-
depth analysis [208,209] . The remainder of this section will summarize the results of combinatorial studies on
HEAs taken from the literature that illustrate the improvements in corrosion resistance achieved so far.

It is well known that Cr is a useful element to improve corrosion resistance, and this result has also been
[210]
verified for many HEA systems . Thus, a Cr-containing HEA system with elements that show a low
[210]
thermal neutron absorption cross-section is a prime candidate for nuclear applications . Xiang et al.
studied the effect of Cr addition in a Mo VNbTi system on the microstructure and properties, including
0.5
[210]
corrosion resistance . The corrosion resistance tests for the Mo VNbTiCr HEAs (x = 0, 0.25, 0.5, 0.75,
0.5
x
1.0, 1.5, and 2.0, denoted as Cr , Cr , Cr , Cr , Cr , Cr , and Cr , respectively) was carried out in
0 0.25 0.5 0.75 1.0 1.5 2.0
superheated steam at 400 °C at 10.3 MPa in a static autoclave which is in accordance with ASTM G2/G2M
guidelines. The weight gain per unit surface area was measured after 10, 20, 30, 40, 50, 60, and 70 days. The
weight gain for each sample was compared to that of Zr-4 alloy (Zr-1.41Sn-0.21Fe-0.10Cr), which is
[210,211]
commonly used as fuel rod cladding in nuclear reactors due to its excellent corrosion resistance . The
results are depicted in Figure 18A, where the weight gain decreases with adding Cr, except for the Cr alloy,
1.5
which may be due to defects. All the compositions outperform the Zr-4 alloy showing much lower weight
gain. This HEA system shows significantly improved corrosion resistance compared to a state-of-the-art
alloy used in current applications, illustrating the potential of HEAs to achieve incredible improvements in
corrosion resistance properties.

Q235 steel is a common structural steel used in many applications, but it often requires a coating to be used
[212]
in corrosive environments . A HEA coating with good corrosion resistance can offer protection to the
[212]
Q235 steel without degradation to its mechanical properties . Qiu et al. explored the effect of composition
[212]
on corrosion resistance in the Al CrFeCo CuNiTi . The addition of Co to the system leads to a more
2 x
positive corrosion potential which implies a higher corrosion resistance especially compared to the control
Q235 steel, as seen in Figure 18B. The authors mention that severe elemental segregation can lead to the
formation of micro-potentials during potentiodynamic polarization tests which can lead to micro-corrosion
and accelerate the corrosion process. The authors also note that the equiaxed grain structure observed in the
HEAs also leads to improved corrosion resistance. Qiu et al. also conducted a similar study on Al 2
[213]
CrFeCoCuNi Ti . Their results are illustrated in Figure 18C. It was also found that the corrosion
x
resistance increased with increasing Ni content and then decreased. The increase in corrosion resistance is
because the Ni element has a high corrosion resistance which contributes to the improved corrosion
resistance of the alloy. However, as the Ni content increases further beyond Ni , the elemental segregation
1.0
increases greatly, which leads to the formation of micro-potentials that accelerate the corrosion process.
[214]
Ti-Zr-based HEAs have been suggested as potential biomedical implant materials . These implants
invariably undergo friction wear over long periods, and the complex chemical environment of the human
body also leads to corrosion. Thus, a comprehensive understanding of the corrosion and wear resistance of
such HEAs is needed to assess their viability for use as implants. Hua et al. studied the corrosion resistance
of Ti ZrNbTaMo HEAs and compared it to Ti-6Al-4V, which has long been favored for biomedical
x
[215]
applications . The corrosion resistance on these alloys is depicted through the potentiodynamic
polarization curves in Figure 18D. The Ti ZrNbTaMo composition shows the highest corrosion
[214] 0.5
resistance . SEM image analysis of all the tested compositions showed that no pitting occurred after the
potentiodynamic polarization tests, which points to the high corrosion resistance of these alloys. Further