Evolution of microstructure in advanced ferritic-martensitic steels under irradiation: the origin of low temperature rad
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Evolution of microstructure in advanced ferritic-martensitic steels under irradiation: the origin of low temperature radiation embrittlement S. Rogozhkin1,2, A. Nikitin1,2, N. Orlov1,2, A. Bogachev1,2, O. Korchuganova1,2, A. Aleev1,2, A. Zaluzhnyi1,2, T. Kulevoy1,2, R. Lindau3, A. Möslang3, P. Vladimirov3 1 State Scientific Centre of the Russian Federation – Institute for Theoretical and Experimental Physics of National Research Centre “Kurchatov Institute”, 117218 Moscow, Russia 2 National Research Nuclear University “MEPhI”, 115409 Moscow, Russia 3 Karlsruhe Institute of Technology, 76344 Karlsruhe, Germany ABSTRACT Advanced reduced activation ferritic/martensitic steels and oxide dispersion-strengthened steels exhibit significant radiation embrittlement under low temperature neutron irradiation. In this study we focused on atom probe tomography (APT) of Eurofer97 and ODS Eurofer steels irradiated with neutrons and heavy ions at low temperatures. Previous TEM studies revealed dislocation loops in the neutron-irradiated f\m steels. At the same time, our APT showed early stages of solid solution decomposition. High density (1024 m–3) of ~3–5 nm clusters enriched in chromium, manganese, and silicon atoms were found in Eurofer 97 irradiated in BOR-60 reactor to 32 dpa at 332°C. In this steel irradiated with Fe ions up to the dose of 24 dpa, pair correlation functions calculated using APT data showed the presence of Cr-enriched pre-phases. APT study of ODS Eurofer found a significant change in the nanocluster composition after neutron irradiation to 32 dpa at 330 °C and an increase in cluster number density. APT of ODS steels irradiated with Fe ions at low temperatures revealed similar changes in nanoclusters. These results suggest that irradiation-induced nucleation and evolution of very small precipitates may be the origin of low temperature radiation embrittlement of f\m steels. INTRODUCTION Reduced activation ferritic/martensitic (RAFM) steels and oxide dispersion strengthened RAFM steels are considered as promising structural materials for future fusion and fission reactors with extreme operational conditions at high neutron fluxes (~1013–1014 n/cm2s) and at elevated temperatures (up to 700 °C) . Eurofer97 steel is targeted to be used as structural material for ITER blanket test units and in future versions of fusion reactors [1]. Mechanically alloyed oxide dispersion strengthened ODS Eurofer steel was developed on the base of Eurofer 97 steel to increase creep-rupture resistance [1-2]. ODS Eurofer steel contains numerous nanosized Y2O3 particles (partly coherent with the matrix), which are formed directly after hot isostatic pressing of this material [3-4]. APT study of the initial state of this material has revealed a large number (~2 × 1024 m–3) of ultrafine nanosized (1–4 nm) clusters enriched in Y, O as well as V, N [5]. These dispersed oxide inclusions provide extremely high temperature resistance to ODS steels. Extensive studies of the properties of these materials have been carried out [6-11]. The most com
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