Fluctuations in misfit volume by interstitial carbon atoms contribute to the unusual dislocation loop evolution in high-entropy alloys under irradiation

Dislocation loops play a pivotal role for the irradiation behavior and associated mechanical properties of materials. This study employs advanced transmission electron microscopy, nanoindentation and first-principles calculations to elucidate the impact of interstitial carbon atoms on the evolution of dislocation loops in an Fe_49.5Mn₃₀Co₁₀Cr₁₀C_0.5 high-entropy alloy under ion irradiation at temperatures ranging from 420 °C to 540 °C with a peak dose of 50 DPA. Interstitial carbon atoms have been revealed to broaden the size distribution of dislocation loops, rendering their morphologies more jagged, and consequently inducing a more substantial pinning effect. These outcomes can be attributed to the enhancement of misfit volume fluctuations of the alloying elements, which drives more severe local lattice distortions and larger variation of local chemical environments. As a result, these fluctuations promote the local pinning of dislocation loops, lead to their rugged movement and contribute to the rise in hardening. Our findings bring previously unrecognized insights into the role of interstitial carbon atoms in influencing the nature of dislocation loops in high-entropy alloys, and provide important clues to the design of alloys for nuclear applications.