Self-interstitial atoms (SIAs) are characteristic defects created under extreme conditions (such as under irradiation) in metallic alloys. Austenitic alloys are widely used in nuclear industry. In these alloys, the effects of magneto-chemical interplay on properties of SIAs remain largely unexplored experimentally and theoretically. Despite previous efforts, various open questions remain around diffusion of SIAs, especially in the Fe-rich region. From a theoretical-study point of view, one important challenge comes from a proper treatment of the SIAs properties in paramagnetic systems such as face centered cubic (fcc) Fe-Ni alloys, being the basis of austenitic steels.

An approach allowing efficient modeling of magnetic-alloys properties consists in spin-atomic Monte Carlo simulations using an effective interaction model (EIM), parametrized on density functional theory (DFT) data [1, 2]. In this work, we employ this approach to address the formation and diffusion of SIAs in pure fcc Fe and Ni and in fcc Fe-Ni alloys. As part of this work, this approach enables an explicit consideration of the spin-excitation and the paramagnetism effects on the SIA properties.

We begin our work by performing DFT studies on formation and migration of high-symmetry SIAs in fcc Fe-Ni systems. First, we address these SIAs in pure fcc Fe and Ni. Our results suggest that <100> dumbbells are generally the most energetically favorable SIAs. We have also identified the most probable SIA migration mechanisms in fcc Fe and Ni. In the case of Ni, the obtained migration barriers are in good agreement with the experimental values in literature. No direct measurements of the SIA migration energies in fcc Fe are available to the best of our knowledge, while our results are significantly different than the one extrapolated from measurements in ternary Fe-Ni-Cr alloys.

Then, we study by DFT the formation and migration properties of the SIAs in some Fe-Ni solid solutions. The obtained results allow to determine the correlation between the local chemical environment and the energetic hierarchy of the various SIA configurations.

Finally, we use the DFT data to parameterize the EIM [1] in order to predict quantitatively the SIAs formation and diffusion properties in fcc Fe-Ni alloys as functions of temperature and Ni concentration.

References

[1] K. Li, C.-C. Fu, M. Nastar et al.; Phys. Rev. B, 2022, vol. 106, 024106.

[2] O. Hegde, V. Kulitckii, A. Schneider et al.; Phys. Rev. B, 2021, vol. 104, 184107.