Fabrication and Characterization of Naturally Selected Epitaxial Fe-{111} Y 2 Ti 2 O 7 Mesoscopic Interfaces: Some Poten
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STRUCTURAL materials used in fission and fusion reactor environments are subject to high temperatures, large time-varying stresses, chemically reactive environments, and intense radiation fields.[1] Helium (He) that is produced by transmutation reactions interacts with displacement damage to drive complex microstructural evolutions. Most notably, He, which is insoluble in steels, precipitates as gas bubbles that act as formation sites for growing voids, and weaken grain boundaries over a wide range of temperatures. Nanostructured ferritic alloys (NFA) containing an ultrahigh density of Y-Ti-O nanofeatures (NF) have been found to be remarkably radiation tolerant. The NF–matrix interfaces trap He in harmless, fine-scale bubbles, suppressing swelling and embrittlement.[2,3] The NF also provide TIBERIU STAN, Graduate Student, YUAN WU, Staff Member, and GEORGE R. ODETTE, Professor, are with the Department of Materials Science and Engineering, University of California, Santa Barbara, Santa Barbara, CA 93117. Contact e-mail: tstan@ engineering.ucsb.edu KURT E. SICKAFUS, Professor, is with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37916. HANNAH A. DABKOWSKA, Research Scientist, is with the Brockhouse Institute of Materials Research, McMaster University, Hamilton, ON L8S 4M1, Canada. BRUCE D. GAULIN, Professor, is with the Department of Physics and Astronomy, McMaster University. Manuscript submitted November 1, 2012. Article published online July 10, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
high stable sink densities for defect annihilation and high creep strength due to dislocation pinning.[2–4] Several transmission electron microscopy (TEM) studies on NFA suggest that the NF are complex oxides, primarily fcc pyrochlore Y2Ti2O7. For example, Sakasegawa et al.[5] did scanning transmission electron microscopy (STEM) energy dispersive X-ray (EDX) measurements on NF extracted from the oxide dispersion-strengthened (ODS) alloy MA957 and found that they are nonstoichiometric Y2Ti2O7, with Y/Ti < 1.0 for larger precipitates (5 to 15 nm) and Y/Ti 0.5 for the smallest pyrochlore features. At larger sizes, 15 to 35 nm, the oxides are closer to stoichiometric, with Y/ Ti 1.0. Yamashita et al. also found nonstoichiometric Y2Ti2O7, but generally with a range of Y/Ti slightly greater than 1.[6,7] Klimiankou et al.[8,9] found nearstoichiometric Y2Ti2O7 in a 9Cr NFA using electron energy loss spectroscopy, high-resolution transmission electron microscopy (HRTEM), fast Fourier transform power spectra indexing, and energy-filtered TEM methods. Early X-ray diffraction (XRD) studies by Okuda et al. also indicated the presence of Y2Ti2O7 in a 14Cr model ODS alloy.[10] This observation has been confirmed by Sakasegawa et al.[5] based on XRD measurements of nanopore-filtered oxides extracted from a 9Cr martensitic alloy. Recently, Wu et al.[11] reported a comprehensive TEM characterization study of MA957 in different conditions, using various techniques. This study clearly showed tha
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