Effects of dislocation-trapped helium on mechanical properties of Fe

Iron (Fe) based alloys are widely used in the nuclear industry because the activation of Fe is low and the irradiation data for Fe alloys is abundant. The interaction between helium (He) atoms and defects in Fe alloys is an important issue in fusion reactors, since the rate of He generation is high. In the present study, well-annealed Fe specimens were cold-rolled until the original thickness was reduced by 10% or 40%, and then annealed at 673 or 723 K for 1 h, respectively, to annihilate the vacancy clusters formed during cold rolling. He atoms were implanted at 100 eV without causing displacement damage in the annealed cold-rolled samples, which contained only dislocations. Upon He implantation, the yield stress (lower yield stress) and tensile strength decreased, and the total elongation increased. The former effect became stronger with increasing deformation (elongation induced by cold rolling from 10% to 40%), whereas the latter became weaker.