Irradiation Damage in Dual Beam Irradiated Nanostructured FeCrAl Oxide Dispersion Strengthened Steel
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Irradiation Damage in Dual Beam Irradiated Nanostructured FeCrAl Oxide Dispersion Strengthened Steel 1
A. Richter1, C.-L. Chen2, A. Mücklich3, R. Kögler3 Department of Engineering, Technical University of Applied Sciences Wildau, Bahnhofstrasse 1, 15745 Wildau, Germany 2 Department of Materials Science and Engineering, I-Shou University, Kaohsiung 840, Taiwan 3 Institute of Ion Beam Physics and Materials Research, Research Center Dresden-Rossendorf (FZD), Bautzner Landstraße 400, 01328 Dresden, Germany
ABSTRACT An oxide dispersion strengthened steel is produced which contains Y-Al-Ti-O nanoparticles with an average diameter of 21 nm. HRTEM analysis shows that the chemical composition of the Y2O3 oxide is modified with perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles. Irradiation of these alloys was performed with a dual ion beam system operating simultaneously with 2.5 MeV Fe+ to 31 dpa and 350 keV He+ to 18 appm/dpa. Ion bombardment causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. TRIM calculations for ODS steel indicate a clear spacial separation between vacancies and self-interstitials at which the vacancy distribution is close to the surface and the interstitials are deposited at a deeper position. The helium atoms mainly accumulate in the vacancies. Fine He cavities with diameters of a few nanometers were identified in HRTEM images. Additionally to structural changes, irradiation generated defects also affect the mechanical properties of the ODS steel. These were investigated by nanoindentation, which is a suitable measuring method as the irradiation damage is created within a thin surface layer. A clear hardness increase in the irradiated depth region was observed, which reaches a maximum close to the surface. This indicates the He condensation in the vacancy dominated region predicted by the simulations. INTRODUCTION Nanostructured ferritic oxide dispersion strengthened (ODS) alloy is an ideal candidate for fission/fusion power plant materials, particularly in the use of a first-wall and blanket structure of a next generation reactor. These steels usually contain a high density of Y-Al-Ti-O nanoparticles, high dislocation densities and fine grains. The effect of irradiation on ODS alloys has been an important issue and stimulated worldwide investigations in the last decade [1-4]. Displacement damage drives complex microstructural and microchemical evolutions and undergoes interactions with helium, which is a transmutation product gas generated at a high concentration in nuclear reactors [5]. Direct neutron irradiation experiments are limited in terms of a variation of parameters such as fluence and temperature. They are also very time consuming and produce highly reactive material. Therefore, ion irradiation is often performed as a substitute for the true reactor conditions. Dual ion beam irradiation [2, 3, 6] is one of the most popular techniques to explore mechanisms of irradiation induced damage of materials
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