Effect of compositional variations on fuzz evolution in NbMoTaW refractory high-entropy alloys

The formation of helium (He)-induced fuzz is one of the critical challenges that must be addressed for the long-term service of plasma-facing materials in fusion reactors. Refractory high-entropy alloys (RHEAs), represented by NbMoTaW, have emerged as promising candidates in fusion applications due to their notable phase stability and irradiation resistance. However, the specific mechanisms by which compositional variations affect He behavior and the evolution of surface nanostructures remain unclear. This study systematically investigated the influence of compositional heterogeneity on He-induced fuzz formation by examining two typical compositional regions—dendrite and interdendrite—in the NbMoTaW alloy. Experimental results indicated that, under high-fluence He ion irradiation, Nb- and Ta-rich regions exhibited a slightly stronger tendency for nanostructure growth, despite previous reports suggesting that Nb and Ta suppress fuzz formation. First-principles calculations revealed that He had a lower solution energy in Nb- and Ta-rich regions. Further analysis of He–He binding energies indicated only a minor difference between the two regions, likely due to the reduced compositional sensitivity of He–He interactions in the chemically complex environment of high-entropy alloys. Given the similar He–He binding strengths, the lower He solution energy in Nb- and Ta-rich regions was found to promote He aggregation and structural evolution, thereby leading to more vigorous fuzz growth. These findings provided new scientific insights into the understanding and regulation of surface evolution behaviors of high-entropy alloys under fusion conditions.