Interstitial-oxygen induced and magnetically driven HCP-to-FCC transformation in CoCrFeNiO x high-entropy alloy: a first-principles study

ABSTRACTWe report the influences of oxygen interstitials and magnetisms on phase stability and structural transformation of CoCrFeNi high-entropy alloy (HEA) from first-principles calculations. It is found the formation of oxygen interstitials is energetically favourable to occur in face-centred cubic (FCC) CoCrFeNiOx HEA as compared with that in hexagonal close-packed (HCP) one, and at those octahedral sites neighbouring with more Cr or less Ni. Meanwhile, it is determined the HEA prefers FCC over HCP phases when the oxygen concentration exceeds 4.2 and 5.1 at.% with and without considering its magnetisms, respectively. The HCP-to-FCC structural transformation in CoCrFeNiOx HEA could be magnetically driven, accompanied by the significant changes in the atomic magnetic moments in the HEA, particularly with an oxygen interstitial concentration larger than 2.7 at.%. Furthermore, the HCP-to-FCC transformation under hydrostatic pressure in CoCrFeNi and CoCrFeNiOx HEAs is investigated from generalised stacking fault energies, and it is revealed that the synergy effects of oxygen interstitials and magnetisms could facilitate the transformation in CoCrFeNiOx HEA. The coupled interstitials-induced and magnetically driven structural transformation paves a new avenue for the application of HEAs.KEYWORDS: Interstitialsphase transformationsCoCrFeNi high entropy alloymagnetismsfirst-principles calculation Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by National Natural Science Foundation of China [Grant Number 52205433]; the Research Grants Council of the Hong Kong Special Administrative Region [Grant Number 15219018/18E]; Natural Science Foundation of Hunan Province [Grant Number 2022JJ40608]. Moreover, this work was supported in part by the High-Performance Computing Center of Central South University