Fuzz formation in a gradient nanostructured tungsten-rhenium alloy under low-energy and high-flux helium plasma impact

Fuzz growth under high-flux and low-energy helium plasma environment has been of intense interest for the plasma-facing materials research in nuclear fusion. This work investigated the surface morphology and subsurface microstructure changes in a gradient nanostructured tungsten-rhenium (25 atomic %) alloy exposed to 90 eV He plasma (flux: ∼2.8 × 10²² He/m²s) at 1173 K. Compared with coarse-grained counterparts, the nanostructured grains, introduced by ultrasonic shot peening technique, can effectively retard fuzz nucleation at low fluence (∼5.0 × 10²⁴ He/m²), yet undergo full fuzz formation at high fluence (∼5.0 × 10²⁵ He/m²). In addition, at the low fluence, fuzz initiates as nanoscale protrusions with pronounced convex curvature relative to the substrate; at the high fluence, near-surface He bubble saturation precedes morphological transition. Our findings suggest that fuzz growth may be a self-sustained process governed by surface diffusion, which provides new insights into the fundamental understanding of fuzz formation in plasma-facing materials.