Defect and void evolution in oxide dispersion strengthened ferritic steels under 3.2 MeV Fe+ ion irradiation with simultaneous helium injection

In an attempt to explore the potential of oxide dispersion strengthened (ODS) ferritic steels for fission and fusion structural materials applications, a set of ODS steels with varying oxide particle dispersion were irradiated at 650 degrees C, using 3.2 MeV Fe+ and 330 keV He+ ions simultaneously. The void formation mechanisms in these ODS steels were studied by juxtaposing the response of a 9Cr-2WVTa ferritic/martensitic steel and solution annealed AISI 316LN austenitic stainless steel under the same irradiation conditions. The results showed that void formation was suppressed progressively by introducing and retaining a higher dislocation density and finer precipitate particles. Theoretical analyses suggest that the delayed onset of void formation in ODS steels stems from the enhanced point defect recombination in the high density dislocation microstructure, lower dislocation bias due to oxide particle pinning, and a very fine dispersion of helium bubbles caused by trapping helium atoms at the particle-matrix interfaces. (C) 2000 Elsevier Science B.V. All rights reserved.