A dual ion irradiation study of helium–dpa interactions on cavity evolution in tempered martensitic steels and nanostructured ferritic alloys

Abstract

Cavity evolutions in a normalized and tempered martensitic steel (TMS) and two nanostructured ferritic alloys (NFA) under Fe3+ and He+ dual ion beam irradiations (DII) at 500°C and 650°C were characterized. The irradiation conditions encompass a wide range of displacement per atom damage (dpa), He and He/dpa. The 500°C DII produced damage and He levels of ≈10–47dpa and ≈400–2000appm, respectively. Transmission electron microscopy (TEM) showed that DII of a 8Cr TMS, at 500°C to up to 60dpa and 2100appm He, produced a moderate density of non-uniformly distributed cavities with bimodal sizes ranging from ≈1nm He bubbles to ≈20nm faceted voids, and swelling ≈0.44%. In contrast, the same irradiation conditions produced only small ≈1.3nm diameter bubbles and swelling of ≈0.05% in the NFA MA957. Similar bubble distributions were observed in MA957 and a developmental NFA DII at 650°C up to ≈80dpa and ≈3900appm He. These results demonstrate the outstanding He management capability of the oxide nano-features in the NFA. The various data trends are shown as a function of dpa, He, He/dpa and He*dpa.