The transport and fate of helium in martensitic steels at fusion relevant He/dpa ratios and dpa rates

Understanding, modeling and managing the effects of He and displacement damage on microstructural evolution and property changes are primary objectives of fusion materials research. We recently implemented an approach for producing controlled He-to-dpa ratios under neutron irradiation using a novel α-implantation technique. Thin 1–4 μm NiAl coatings were deposited on Eurofer-97 TEM discs to produce a uniform He deposition zone of 6–8 μm. The test matrix is aimed at characterizing the transport, fate and consequences of He and He-to-dpa ratio variation on alloys with a wide range of starting microstructure. We explore the effect He-to-dpa ratio and temperature on the microstructure of conventionally processed Eurofer-97. Bubbles were found at all irradiation temperatures, with estimated maximum diameters of ∼12, 6.9 and 1.4 nm at 500 °C (∼9 dpa and 372 appm He), 400 °C (∼3.9 dpa and 82 appm He) and 300 °C (∼3.9 dpa and 89 appm He), respectively.