**4. Conclusions**

In this work, the elastic constants, *C*11, *C*12, *C*44, bulk modulus and shear modulus of FeCrAl alloys were calculated with molecular dynamics methods for compositions with 1~15 wt.% Cr and 1~5 wt.% Al at temperatures from 0 K to 750 K. The effects of Cr and Al concentrations and temperature on elastic constants have been explored. The results indicate that *C*11, *C*12, *C*44, bulk modulus and shear modulus show different dependencies on the concentrations of Cr and Al. In particular, for alloys with Al concentration >3 wt.%, the bulk modulus decreases with the increase of Cr concentration. However, for Al concentration of 1–5 wt.%, the shear modulus decreases with the increase of Cr concentration. Both results are consistent with experimental results. An decrease of elastic constants with increasing temperature was also observed in the present work, which is consistent with experimental results. Investigation on elastic properties of defect-containing alloys have shown that vacancies, voids, interstitials and Cr-rich precipitations have different effects on elastic properties of FeCrAl alloys. Vacancies and voids result in the decrease of elastic properties, while interstitials could result in the increase of bulk modulus but decrease of shear modulus. The formation of Cr-rich precipitates increases the elastic properties, which is independent of the number and volume of precipitates. Therefore, the present results indicate that compared to the concentration effect, the radiation defects show different effects on elastic properties. Furthermore, when the radiation effects are predicted, e.g., radiation hardening, not only the contribution from the interaction between dislocation and radiation defects, but also the radiation defects before the interactions with dislocations, should be considered. All these results provide a new understanding to develop and apply the FeCrAl alloy in AFT design.

**Author Contributions:** Conceptualization, N.G. and X.W.; methodology, H.D.; software, M.Y.; validation, M.Y. and N.G.; formal analysis, H.D. and M.Y.; investigation, H.D. and M.Y.; resources, H.D.; data curation, Y.D.; writing—original draft preparation, H.D.; writing—review and editing, N.G. and W.S.; visualization, H.D.; supervision, N.G.; project administration, N.G.; funding acquisition, N.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the National Natural Science Foundation of China (Grant number. 12075141 and 11675230). WS acknowledges the support provided by the U.S. Department of Energy through the Office of Fusion Energy Sciences (DE-AC05-76RLO-1830).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.

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