# Irradiation-Induced Phase Stability in Ti- and Nb-Containing Nickel-Based High-Entropy Alloys at 500 °C

## TL;DR

This study compares how two nickel-based high-entropy alloys respond to irradiation, finding that Ti-containing alloys maintain structural stability better than Nb-containing ones.

## Contribution

The novel contribution is identifying how Ti and Nb influence irradiation-induced phase stability through solute-defect interactions and structural recovery mechanisms.

## Key findings

- Ti-containing HEA preserves L12-ordered structure better than Nb-containing HEA under irradiation.
- Ti allows vacancy mobility, aiding thermal reordering, while Nb traps vacancies, suppressing recovery.
- TiHEA shows higher irradiation hardening (27%) compared to NbHEA (23%) due to better precipitate order preservation.

## Abstract

This study investigates the irradiation response of two L12-strengthened HEAs, (Ni2Co2FeCr)92Ti4Al4 (TiHEA) and (Ni2Co2FeCr)92Nb4Al4 (NbHEA), subjected to 6.4 MeV Fe3+ irradiation at 500 °C up to 30 dpa. Transmission electron microscopy (TEM) and atom probe tomography (APT) consistently showed that the Ti-containing HEA maintains L12-ordered structure and compositional stability better than Nb-containing alloys under irradiation. This difference is attributed to the distinct solute–defect interactions. Ti imposes a weaker hindering effect on vacancy mobility, allowing vacancies to remain mobile and participate in thermal reordering processes that counteract ballistic mixing, whereas Nb acts as a strong vacancy trap, suppressing the diffusion required for structural recovery. Irradiation-induced dislocation loops in the two alloys further exhibited different characteristics. TiHEA showed larger loops at lower number density, and NbHEA exhibited a higher density of smaller loops, consistent with their respective stacking fault energies and loop mobility. Nanoindentation results indicated that TiHEA exhibited a slightly higher irradiation hardening rate (27%) than NbHEA (23%), likely associated with a stronger order-strengthening contribution, given the better preservation of precipitate order in TiHEA under irradiation. These findings show the critical role of solute addition in designing radiation-tolerant high-entropy alloys.