Phase instability of Al/Ti-bearing FeCoNiCr high-entropy alloys under prolonged high-temperature irradiation

The multicomponent high-entropy alloys (HEAs) have proven to possess superior radiation tolerance for the potential nuclear application. However, their longstanding phase stability under the relevant environment remains a critical and contested concern. This study investigated the phase stability of two distinct FeCoNiCr-based HEAs: an Al-bearing solid-solution alloy and a Ti-bearing precipitation-hardened alloy irradiated with 3 MeV Ni ions at 873 K to a peak displacement damage of ∼107 dpa. Utilizing transmission electron microscopy (TEM) and atom probe tomography (3D-APT), we demonstrated that the HEAs underwent severe radiation induced segregation (RIS) at irradiation defects. For the Al-bearing HEA, the local chemical instability triggered the heterogeneous nucleation of Ni₃Al-L1₂ precipitates around voids and dislocation loops. In contrast, the Ti-bearing HEA exhibited a depth-dependent response for the phase stability. In the peak damage region, high displacement rates caused the complete disordering of pre-existing L1₂ precipitates; conversely, in regions with lower damage rates, thermal effects led to the survival and re-precipitation of ordered phases. Additionally, we identified the formation of M₂₃C₆ carbides in the Al-bearing HEA, which was attributed to extrinsic carbon contamination during ion irradiation. These findings highlight that long-term phase stability of HEAs is dynamically controlled by the interplay of ballistic mixing and RIS-mediated solute transport. © 2026 Elsevier B.V.