A microstructural examination of the mechanical response of FeCrNi alloys irradiated at 365°C using isotopic tailoring to produce different He/dpa ratios

A series of model Fe15CrxNiyP alloys with x = 25 or 45 and y = 0.001 or 0.04 wt.% were examined following irradiation to 10.3 dpa at 365°C. These alloys were irradiated both doped and undoped with the ⁵⁹Ni isotope to produce two levels of He generation during irradiation. This latter variable produced average He/dpa values of approximately 1 and 16 appm He/dpa in the undoped and doped cases, respectively. Microscopy examination indicates that the major influence of a high He/dpa ratio is to induce a higher void number density and a lower average void size than in identical alloy conditions with low He/dpa. The total swelling is not substantially affected, however. Compositional and thermal-mechanical treatment variables were found to influence the swelling behavior as much as the He production rate. However, in all cases the swelling was low, and irradiation-induced microstructures were similar regardless of starting condition. This convergence in microstructure is reflected in the mechanical properties where similar room temperature tensile properties were measured on irradiated specimens regardless of material starting condition.