Microstructure evolution of helium irradiated (NbMoTaW)V50 films with nanochannel structure under nanoindentation

Material degradation due to precipitation of implanted helium (He) is a major concern in nuclear facilities. Conventional structural design strategies are only limit the nucleation and accumulation of He bubbles, by contrast, we have prepared (NbMoTaW)V50 films with a unique nanochannel structure by taking advantage of the free surfaces exhibiting benefits in He management and release behavior. The films were irradiated with 50 keV high-energy He+ ion irradiation. The microstructure of the irradiated films revealed that the nanochannels are decorated with He bubbles, while the number of He bubbles within the grains is minimal. Nanoindentation tests revealed that He+ ion irradiation enhances the film’s creep resistance. Furthermore, the He atoms accumulated on the free surface of the grain boundaries tends to migrate and coalesce into He clusters under the influence of stress, subsequently releasing to the surface through nanochannels, thus mitigating the irradiation-induced volume swelling.