Effects of interactions between dislocations and/or vacancies and He atoms on mechanical property changes in Ni

It is well known that helium (He) generated by (n, α) nuclear reactions in metals and alloys irradiated with high-energy particles prompts not only the nucleation of interstitial-type dislocation loops, but also the nucleation of voids, which degrades mechanical properties. In the present study, He atoms were implanted at 150 eV without causing displacement damage in Ni containing either dislocations, vacancies or a combination of both. The results showed that upon He implantation, the ultimate tensile strength increased and total elongation decreased in samples containing both dislocations and vacancies. However, it was also found that in samples with He trapped by dislocations, where the He concentration decreased with increasing sample depth, nickel increased both the ultimate tensile strength and total elongation at 300 K, but that the effect of He disappeared at 573 K. In addition, He trapped by vacancies did not strongly affect the ultimate tensile strength or total elongation in samples containing only vacancies.