Helium-ion microscopy, helium-ion irradiation and nanoindentation of Eurofer 97 and ODS Eurofer

Understanding of unsolved details of helium embrittlement requires experimental evidence for dedicated sets of materials and over a wide range of irradiation conditions. The study is focussed on the comparison of the reduced-activation ferritic-martensitic 9%Cr steel with its oxide dispersion strengthened (ODS) counterpart with respect to irradiation-induced hardening. Imaging and He-ion irradiation in the He-ion microscope at 30 ºC in a wide range of appm He (from 0.9 x 1E2 to 1.8 x 1E6) and displacements per atom (from 3 x 1E-3 to 65) were combined with post-irradiation nanoindentation in order to detect blistering and irradiation-induced hardness changes. The applicability of this combination of techniques is demonstrated and pros and cons are discussed. We have found that the irradiation-induced hardness increase is higher and the onset of significant hardening tends to occur at lower fluence for Eurofer 97 than for ODS Eurofer, indicating that the presence of oxide nanoparticles is efficient to reduce the detrimental effect of He under the applied irradiation conditions.