Ion Implantation Induced Damage in Oxide Dispersion Strengthened Steels and FeCr Alloys Investigated by DB and cDB

FeCr alloys and oxide dispersion strengthened (ODS) FeCr steels are candidates for structural materials for Generation IV and fusion reactors, owing their advantageous physical and chemical properties for such applications as, e.g., resistance against oxidation, creep and radiation.
For an optimal steel composition, depending on the application, it is important to understand how alloying components and oxide additives affect the materials behaviour to irradiation. For this purpose, Fe-Cr alloys have been employed as model materials in irradiation experiments and subsequent characterization of irradiation damage. Ion implantation was demonstrated an efficient tool for simulation of radiation damage similar to that in fission/fusion power plant materials, but without any induced activation.
FeCrNiSiP samples with two Cr contents of 5 wt.% and 9 wt.% were implanted with 5 MeV Fe ions at different temperatures with a damage of 0.1 displacements per atom (dpa) and 0.5 dpa, respectively. The influence of the alloying elements on the evaluation of the damage after ion implantation was investigated for the complete FeCrNiSiP alloy and separately for each FeCr added with the single alloying elements.
Furthermore model Fe14wt.%Cr alloys and two ODS Fe14Cr steels with 0.3wt.%Y2O3 and with and without Ti and W additions were implanted at low temperature with 1 MeV Fe ions up to a high damage of 15 dpa.
A slow positron beam has been used in order to investigate the depth dependence of the ion implantation induced vacancy-type defect in the materials by single Doppler broadening (DB) measurements with positron energies from 30eV to 35keV, corresponding to a depth from 1 nm down to 3 µm. Furthermore, coincidence DB measurements at selected positron energies were applied for a more precise examination of a possible defect decoration of the open volume by alloying elements.
Slow positron beam techniques turned out to be an effective tool for the characterization of open-volume defects after ion implantation. It could be shown that a Ni addition to FeCr led to an increase of the open-volume defects after ion implantation, whereas Si or P reduced them. A minimal damage could be detected for the complete alloy FeCrNiSiP.
A lower Cr content of 5wt.% is advantageous against 9wt.% for a defect annealing during implantation at temperatures below 450 °C. At 450 °C all defects annealed out already during implantation.
The influence of Y2O3 nanoparticles on the stabilization of defects in FeCr steels could be demonstrated by DB and cDB measurements and will be discussed in detail.