HRTEM Study of Oxide Nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y 2 O 3 ODS Steel
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1215-V02-04
HRTEM Study of Oxide Nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y2O3 ODS Steel Luke L. Hsiung1, Michael J. Fluss1, Mark A. Wall1, Akihiko Kimura2 1
Lawrence Livermore National Laboratory Physical and Life Sciences Directorate L-352, P.O. Box 808 Livermore, CA, U.S.A. 2
Institute of Advanced Energy Kyoto University, Gokasho, Uji Kyoto 611-0011, Japan ABSTRACT Crystal and interfacial structures of oxide nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y2O3 ODS steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainlyY4Al2O9 (YAM) with a monoclinic structure. Orientation relationships between the oxide and matrix are found to be dependent on the particle size. Large particles (> 20 nm) tend to be incoherent and have a spherical shape, whereas small particles (< 10 nm) tend to be coherent or semi-coherent and have faceted interfaces. The observations of partially amorphous nanoparticles lead us to propose a three-stage mechanism to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels. INTRODUCTION Development of high-performance structural materials for first wall and breeding-blanket components, which will be exposed to high fluxes of high energy (14 MeV) neutrons from the deuterium-tritium fusion, is one of the major challenges in materializing future fusion reactors. The choice of structural materials for the first wall and blanket to a large degree dictates the design of the reactor systems. The selection of suitable structural materials is based on conventional properties (such as thermophysical, mechanical, and corrosion and compatibility), low neutron-induced radioactivity, and resistance to radiationinduced damage phenomena like material hardening/embrittlement and/or dimensional instability caused by void- and helium-driven swelling [1]. Oxide dispersion strengthened (ODS) F/M and ferritic steels, which produced by mechanical alloying the elemental (or pre-alloyed) metallic powder and yttria (Y2O3) oxide powder consolidated by hot extrusion or hot isostatic pressing, are advanced structural materials with a potential to be used at elevated temperatures due to the dispersion of thermally stable oxide nanoparticles into the F/M matrix. The use of ODS steels should improve creep strength and oxidation/corrosion resistance at high temperatures and consequently increase the operating temperature of first wall and blanket structures in the future fusion/fission hybrid reactors by approximately 700 ºC or higher [2]. The performance of ODS steels is largely determined by the particle size and the stability of dispersed oxide nanoparticles. Although Y2O3 has been selected as the major dispersed oxide, its particle size increases during the consolidation and thermomechanical treatment of ODS steels. To enhance the stability of oxide particles, titanium and alumi
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