Page 73 - Read Online

Page 14 of 17 Xiao et al. Microstructures 2023;3:2023006 https://dx.doi.org/10.20517/microstructures.2022.26

(6) At the present time, studies are mainly focused on the static tensile properties of the HEAs with
hydrogen charging and intermediate temperatures. More importantly, the dynamic mechanical properties
(fatigue, creep and fatigue/creep crack propagation) should be evaluated under in-situ hydrogen gas
charging environments and intermediate temperatures. Subsequently, associated physical-based lifetime
prediction models of HEAs should be developed. These studies are expected to ensure the reliability and
safety of EE-resistant HEAs in engineering applications.

CONCLUSIONS
HEAs have received growing interest from metallurgical scientists and engineers due to their special
microstructures and superb mechanical properties, which can potentially be used in many important
engineering fields, including aerospace, nuclear power and chemical processing applications. In the present
work, we have critically reviewed the recent major achievements in EE behavior and the associated
underlying mechanisms of HEAs. In particular, two critical EE phenomena (HE and ITE) have been
separately summarized. The representative HE- and ITE-resistant HEAs and the corresponding micro-
mechanisms have been discussed in detail. Although some advances have been achieved, research on this
topic is only just starting to develop at present and there are numerous unaddressed critical issues. In future
work, to further accelerate the design of novel HEAs with superior resistance to HE and/or ITE, significant
efforts should be made to fundamentally elucidate the hydrogen (oxygen) diffusion behavior and associated
static/dynamic mechanical responses of HEAs. In the meantime, compositional optimization and structural
regulation should be systematically studied to improve the resistance to HE and ITE of HEAs. Finally,
atomic-scale microstructural characterizations are required to directly observe the hydrogen distribution
and better understand the HE mechanism in HEA systems.

DECLARATIONS
Authors’ contributions
Organized the literature review and drafted the original version: Xiao B, Yang T
Revised the manuscript: Liu S, Zhang J, Zhou Y, Li Q, Hou J, Xiao W, Zhang J, Zhao Y, Liu CT, Xu L
Conceived and supervised the project: Yang T, Zhao Y

Availability of data and materials
Not applicable.

Financial support and sponsorship
This project was financially supported by the Hong Kong Research Grant Council (RGC) (Grant No. CityU
21205621, 11214820, 11209021, and C1017-21G), the National Natural Science Foundation of China (Grant
No. 52101151 and 52101135), and the Shenzhen Science and Technology Program (Grant No.
SGDX20210823104002016 and RCBS20210609103202012).

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.