Study of residual stress and vacancy defects in oxide dispersion strengthened steels

This study was focused on commercial oxide-dispersion strengthened (ODS) steels - MA 956 (20%Cr), ODM 751 (16%Cr) and ODS Eurofer (9%Cr), developed for fuel cladding of GEN IV reactors. The ODS steels are described in order to comparison their microstructure features. Vacancy defects were observed by Doppler Broadening Spectroscopy (DBS) and Positron Annihilation Lifetime Spectroscopy (PALS). Residual stress proportional to all kinds of defects was investigated by Magnetic Barkhausen Noise (MBN) measurement. The positron techniques demonstrated the highest defect concentration for ODS Eurofer followed by MA 956. The lowest defect density belongs to ODM 751; although these defects are the largest (three or four vacancy clusters). MA 956 and ODS Eurofer have di-vacancies in predominance. MBN results are in a good accordance with positron techniques. The highest residual stress is for ODS Eurofer, followed by MA 956. Finally, the lowest residual stress proportional to hardness is found for ODM 751. (c) 2012 TheAuthors Published by Elsevier B.V. Selection and/or peer-review under responsibility of Organizing Committee.Peer reviewe

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