Point defects and primary radiation damage in Co-free Fe-Ni-Cr-Mn high-entropy alloys from molecular dynamics

Abstract

Co-free Fe-Ni-Cr-Mn high-entropy alloys (HEAs) are candidates for nuclear structural applications. We used molecular dynamics with the EAM-21 potential, stiffened at short range, to study five HEAs that have been irradiated experimentally: Fe37Ni34Cr16Mn13 (ES1), Fe35Ni35Cr15Mn15 (P35), Fe46Ni22Cr15Mn17 (Y3), Fe27Ni28Cr18Mn27 (Kumar) and Fe30Ni30Cr10Mn30 (C30). They were compared with pure Ni, Fe60Ni40, the Fe70Ni10Cr20 model alloy of 316L, and Fe50Ni34Cr16, which is ES1 with Mn replaced by Fe. We calculated stacking fault energies, threshold displacement energies, point-defect formation and migration energies, and 1015 displacement cascades from 5 to 40 keV at 300 and 823 K. The stacking fault energy follows the Ni content: 19-44 mJ/m^2 in the alloys and 113 mJ/m^2 in Ni. Compared with the Mn-free alloys, the HEAs have lower threshold displacement energies (48-56 against 64-74 eV) and lower dumbbell formation energies, and Mn is the element most transported by interstitials. All the concentrated alloys leave about the same number of Frenkel pairs, 56-72 at 40 keV, half the number in Ni. At 40 keV, 54-58% of the interstitials are in clusters in the HEAs, against 67-71% in Fe60Ni40, Fe70Ni10Cr20 and Fe50Ni34Cr16 and 82% in Ni. At the same cluster size, clusters of 4-12 interstitials are faulted about half as often in the HEAs, and this does not follow the stacking fault energy. The surviving interstitials are enriched in Mn in the HEAs and in Ni in the Mn-free alloys, and depleted in Cr. The results support direct loop formation in cascades in Fe60Ni40 and Fe70Ni10Cr20 and less of it in ES1.