Dynamic behavior of helium in nanocrystalline tungsten film by thermal desorption and internal friction

• Post-annealing analysis demonstrated the diffusion and aggregation of He atoms/clusters promoted W film swelling and interfical embrittlement; • TDS measurements further quantify a He desorption activation energy of 0.38 eV, indicating atomic escape from surface defects or stabilized clusters; • He migration with preferential diffusion along grain boundaries and dislocation networks exhibited an activation energy of 0.42 eV, consistent with Gorsky relaxation mechanisms. Tungsten (W) has been considered a primary candidate for plasma-facing materials due to its superior properties. However, significant challenges remain due to helium-induced (He-induced) irradiation damage, particularly the formation of He clusters and bubbles, surface morphology changes, and void swelling. In this study, He-charged W nanocrystalline films (grain size < 100 nm) were fabricated via a radio-frequency (RF) magnetron sputtering under a mixture of helium (He) and argon (Ar) atmospheres. The results revealed that grain boundaries (GBs) and dislocations serve as the dominant fast diffusion pathways for He atoms, providing effective diffusion paths with an activation energy of 0.42 eV, significantly lower than that associated with vacancy-mediated diffusion through the bulk lattice. The increase in He bubble size after post-annealing at 400°C can be attributed to temperature-dependent He diffusion and aggregation. Thermal desorption spectroscopy analysis revealed a distinct He desorption peak between 550–650 K, corresponding to an activation energy of 0.38 eV, likely resulting from the detrapping of He atoms from helium-vacancy complexes or larger He clusters on the surface. Internal friction spectra exhibited frequency- and temperature-dependent relaxation peaks related to the Gorsky effect, indicating that the low-temperature internal friction peak is due to He diffusion along GBs and dislocations. This work provides an effective method for studying the dynamic behaviors of He atoms in nanocrystalline metals.