HRTEM Study of the Role of Nanoparticles in ODS Ferritic Steel under Dual-Ion Irradiation
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HRTEM Study of the Role of Nanoparticles in ODS Ferritic Steel under Dual-Ion Irradiation Luke Hsiung1*, Scott Tumey1, Michael Fluss1, Yves Serruys2, and Francois Willaime2 1
Lawrence Livermore National Laboratory Physical and Life Sciences Directorate Livermore, CA94551, U.S.A. 2 Service de Recherches de Métallurgie Physique (CEA) Gif-sur-Yvette 91191, France ABSTRACT Structures of nanoparticles and their role in dual-ion irradiated Fe-16Cr-4.5Al-0.3Ti-2W0.37Y2O3 (K3) ODS ferritic steel produced by mechanical alloying (MA) were studied using highresolution transmission electron microscopy (HRTEM) techniques. The observation of Y4Al2O9 complex-oxide nanoparticles in the ODS steel imply that decomposition of Y2O3 in association with internal oxidation of Al occurred during mechanical alloying. HRTEM observations of crystalline and partially crystalline nanoparticles larger than ~2 nm and amorphous cluster-domains smaller than ~2 nm provide an insight into the formation mechanism of nanoparticles/clusters in MA/ODS steels, which we believe involves solid-state amorphization and re-crystallization. The role of nanoparticles/clusters in suppressing radiation-induced swelling is revealed through TEM examinations of cavity distributions in (Fe + He) dual-ion irradiated K3-ODS steel. HRTEM observations of helium-filled cavities (helium bubbles) preferably trapped at nanoparticle/clusters in dual-ion irradiated K3-ODS are presented. INTRODUCTION One of the major challenges in designing future fusion reactors is to develop the highperformance structural materials for first wall and diverter components, which will be exposed highenergy neutrons (14 MeV) from the deuterium-tritium fusion and helium (He) and hydrogen (H) from in (α, n)- and (n, p)-transmutation reactions [1]. The choice of structural materials dictates the design of the fusion reactor systems. In particular, the allowable power plant operating temperature, the choice of coolant, and the power conversion system are critically dependent on the performance characteristics of the materials. Oxide dispersion strengthened (ODS) steels, which produced by mechanical alloying of the elemental (or pre-alloyed) metallic powder with yttria (Y2O3) oxide powder and consolidated by hot extrusion or hot isostatic pressing, are a class of advanced structural materials with a potential to be used at elevated temperatures due to the dispersion of thermally stable oxide nanoparticles into the matrix. ODS steels are resistant to radiation-induced swelling and have improved creep strength and oxidation/corrosion resistance at elevated temperatures compared to conventional steels. Thus an operating temperature of the first wall in future fusion of > 700 ºC [2] is possible, resulting in an improved efficiency of ≥ 40% [3]. Since no prototype fusion reactors currently exist, it is difficult to directly evaluate the effects of high-energy neutron and transmutation gases on the first wall and diverter components of a * Corresponding author. Tel.: +1‐925 424 3125; fax: +1‐925 424 3815
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