Low temperature tensile properties of steels containing high concentrations of helium

Due to the high particle energies, the radiation conditions in spallation targets are characterized by very high helium production rates. We simulated this fast helium generation by implantation of α-particles into AISI 316L and DIN 1.4914 specimens and studied its effect on the mechanical properties by subsequent tensile tests at 25 and 300 °C, respectively. Up to He-concentrations of 0.5 at.% the observed hardening and embrittlement can be attributed to displacement-induced defects. However, at around 1 at.% He, the observed increase in yield stress and decrease in ductility are considerably outside the trend lines for the dpa dependence. Such a ‘critical’ He-concentration was also inferred from hardness measurements on dual-beam irradiated specimens.The microstructure of the implanted specimens shows the usual features appearing in steels after low temperature irradiation (‘black dot’ damage and dislocation loops). No visible (>1 nm) bubbles could be detected in the specimens, including those containing 1 at.% He.