Various oxide dispersion strengthened steels (PM2000, MA956, ODM751, ODS Eurofer) were investigated using positron annihilation lifetime spectroscopy. Preliminary characterization of the vacancy-type defects and the yttria nanoparticles were reported here. The interpretation of the experimental data considers also the results of magnetic Barkhausen noise measurements as well as SEM and transmission electron microscopy investigations. Significant differences due to the presence of the yttria oxides (namely Y2O3) were observed in the studied materials in comparison to conventional ferritic/martensitic steels (e.g. Eurofer). Higher positron mean lifetime in oxide dispersion strengthened steels is, however, not only due to the presence of dispersoids, but also a result of vacancy agglomeration (clusters of 6–8 vacancies) which were confirmed in recrystallized ODM751 and MA956 materials. On the other hand, positron trapping at dislocations was observed in the as-extruded oxide dispersion strengthened Eurofer in contrast to the other, recrystallised, materials where the high temperature treatment had led to the static recovery of these defects. It was suggested that some defects which were present (dislocations, vacancy clusters, dispersoids) and affect positron trapping in the materials were also important pinning sites for the magnetic domains. This was reflected by a shift of the signal peak in the Barkhausen noise spectra. The present complementary study provides more comprehensive information about materials microstructure and could support the interpretation of the physical/mechanical testing results (hardness, fracture mechanics etc.) obtained on these materials.

NDT Study of Oxide Dispersion Strengthened Steels. V.Krsjak, Z.Szaraz, J.Degmova, P.Hähner: Journal of Physics - Conference Series, 2011, 262[1], 012034