Hybrid diffusive-displacive helium outgassing in Cu/Nb multilayer composites

Gas generation degrades material properties in nuclear applications. The construction of self-assembled bubble channels was proposed to help release gas to the surface. In this study, thermal desorption spectroscopy, in-situ TEM heating and molecular dynamics simulations were carried out to assess the outgassing feasibility in helium-irradiated Cu/Nb multilayers with low structural damage. We found that the formation of outgassing networks has a hybrid diffusive-displacive nature, with diffusive bubble coalescence and crack-induced displacive fracture. The latter could destroy the integrity of the multilayer structure. This suggests that the outgassing strategy making use of self-assembled cavity networks should be carefully designed to avoid large-scale structural failure.