Helium generated in materials by the nuclear reaction (n, α) was generally considered to be harmful. It was well-known that helium prompts not only the nucleation of interstitial-type dislocation loops, but also the nucleation of voids in metals and alloys irradiated with high-energy particles, which degrades their mechanical properties. However, it was found here that helium trapped by dislocations in Ni increased both the ultimate tensile strength and the total elongation.

Can Helium Actually Improve the Mechanical Properties of a Metal? Q.Xu, H.Yamasaki, K.Sato, T.Yoshiie: Philosophical Magazine Letters, 2011, 91[11],  724-30