Study of Oxide-Dispersion-Strengthened Ferritic Steels after Ion Implantation

This paper is focused on four different commercial oxide-dispersion-strengthened ferritic steels (MA 956, ODM 751, MA 957 and ODS Eurofer) with different chromium content and the change of their microstructure after helium ion implantation. The samples were implanted with kinetic energy of ions up to 500 keV and the implantation depth was up to 1.2 μm. The implantation was performed at Institute of Nuclear and Physical Engineering, Slovak University of Technology in Bratislava. The samples were observed prior and after the implantation by positron Doppler broadening spectroscopy with slow positron beam (energy up to 36 keV) which is one of the most suitable techniques due to its sensitivity to surface and subsurface layers up to 1.6 μm. The results showed visible change of defect presence in all samples and defect depth profiles are in a good accordance with SRIM software calculations displaying the Bragg peak. According to measured data, ODS Eurofer (9% Cr) seems to be the most radiation resistant from the group of all investigated steels and MA 956 (20% Cr) as the most radiation affected steel

Positron annihilation studies of Eurofer97/ODS steels after helium ion implantation

The paper briefly reviews our positron annihilation studies performed on Eurofer97 steel and its ODS variant, performed in the last about 20 years. Various aspects of radiation environments foreseen for these materials were experimentally simulated via ion implantation and studied by a combination of non-destructive characterization techniques. The primary characterization tools in these studies were two techniques based on positron annihilation, namely positron annihilation lifetime spectroscopy (PALS) and Coincidence Doppler Broadening (CDB) technique. In addition to bulk studies utilizing conventional radioisotope positron sources, ion-implanted specimens were analysed using slow positron beams. This review summarizes the key findings of these techniques concerning the nature of the radiation resistance of EUROFER/ODS steels

Positron Annihilation Study of RPV Steels Radiation Loaded by Hydrogen Ion Implantation

Specimens of 15Kh2MFAA steel used for reactor pressure vessels V-213 (VVER-440 reactor) were studied by positron annihilation techniques in terms of their radiation resistance and structural recovery after thermal treatment. The radiation load was simulated by experimental implantation of 500 keV H+ ions. The maximum radiation damage of 1 DPA was obtained across a region of 3 µm. Radiation-induced defects were investigated by coincidence Doppler broadening spectroscopy and positron lifetime spectroscopy using a conventional positron source as well as a slow positron beam. All techniques registered an accumulation of small open-volume defects (mostly mono- and di-vacancies) due to the irradiation, with an increase of the defect volume ΔVD ≈ 2.88 × 10−8 cm−3. Finally, the irradiated specimens were gradually annealed at temperatures from 200 to 550 °C and analyzed in detail. The best defect recovery was found at a temperature between 450 and 475 °C, but the final defect concentration of about ΔCD = 0.34 ppm was still higher than in the as-received specimens