Helium behavior in W/Ni bilayer nanocomposite was investigated by neutron reflectometry, transmission electron microscopy (TEM) and density functional theory (DFT) calculation.

Tungsten and its alloy are widely used as target material in spallation neutron sources because of their high neutron production, high melting point, high temperature strength, good thermal conductivity, low vapor pressure and tritium retention.  They are also the candidate materials for plasma-facing components (PFCs) in fusion reactors. The target material in spallation neutron sources and PFCs withstand serious radiation damage, meanwhile, abundant transmutation hydrogen and helium atoms are generated by nuclear reaction. Due to low solubility and migration energy, the helium atoms can easily precipitate and aggregate into helium bubbles that nucleate on vacancies or high excess volume sites (e.g., grain boundaries), and even grow into void, which seriously degrades the physical and mechanical properties of tungsten alloys. Hence, the ability to mitigate radiation-induced defects and control nucleation and growth of helium bubbles is crucial to improving the radiation tolerance of materials.

Resuilts shows that the W/Ni interface is confirmed to be an effective sink for helium atoms, and the helium storage of W/Ni interface can reach saturation at high implantation fluence. Moreover, researchers proposed a mechanism, suggesting that helium atoms trapped at the interface of W/Ni mainly migrate from the W layer. This mechanism enlightens that dispersing nickel-nanoparticles into tungsten can protect tungsten against helium deleterious effect. That is, modulating the constituent of dispersed nano-particles can effectively improve the helium resistant of materials.

The full publication can be found here: https://www.sciencedirect.com/science/article/pii/S0169433219313133?via%3Dihub