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Quantifying helium-bubble swelling in RAFM steels using TEM and the surface-step method
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DOI：10.1016/j.nme.2026.102095.png)
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Abstract
En 中文
In fusion-relevant environments where transmutation helium accumulates, He bubble formation can become a critical damage mechanism in reduced-activation ferritic/martensitic (RAFM) steels because it drives swelling and can degrade mechanical performance. Swelling is often assessed indirectly from surface-step height measurements and nanoindentation mapping, yet their quantitative relationship to the underlying bubble population remains unclear. Here, He bubbles in K-RAFM steels and a Eurofer97-like reference steel were quantified by cross-sectional TEM after 160 keV He implantation and post-irradiation annealing (PIA) at 300-500 degrees C. Bubble size distributions, number densities, and bubble-volume-fraction-based swelling were evaluated and directly compared with step-height- and hardness-based metrics. Bubble nucleation was most evident at 300-400 degrees C through an increase in number density, whereas pronounced coarsening at 500 degrees C led to a sharp increase in swelling. Step height reproduced the temperature-dependent swelling trend, while the nanoindentation hardening response was more closely linked to bubble number density than to bubble size. In addition, sequential H/He implantation revealed a clear He-H synergy, with a stronger enhancement of bubble density and swelling when H was implanted after He (He + H) than in the reverse order (H + He).
Keywords:
Reduced-activation ferritic/martensitic steel (RAFM)
Helium bubble
Swelling
Post-irradiation annealing (PIA)
Helium-hydrogen synergy
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