Microstructural characterization of the ζ- and γ-hydride phases in Zircaloy-2 by Electron Diffraction and Energy-Loss Spectroscopy Techniques.
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Authors
Nikpoor Badr, Nima
Date
Type
thesis
Language
eng
Keyword
Zirconium hydrides , Zircaloy , Transmission Electron Microscopy , Electron Energy Loss spectroscopy , Electron diffraction , Plasmon energy
Alternative Title
Abstract
In this study, the formation of the ζ- and γ-hydride phases in the form of independent bulk precipitates and interfacial ribbons between δ-precipitates and α-Zr matrix was investigated.
Energy-Loss Spectroscopy (EELS) and Nano-Beam Electron Diffraction (NBED) techniques were utilized to characterize nano-hydrides formed in water-quench and furnace-cool conditions. For δ-nano-hydrides, EELS measured two ~10 nm-wide ribbons with plasmon energy (PE) values of 17.4±0.3 eV and ~18.3±0.3 eV (characteristic of the ζ- and γ-phases, respectively) surrounding the δ-core. Complementary NBED characterization of multiple zone axes of the interface, however, did not suggest the existence of the ζ- or γ-phases in the interface.
Next, it was attempted to clarify why the characteristic PE values of the ζ- and γ-phases were observed in the interface. For this purpose, energy-loss spectra of the α-Zr and δ-hydride phases were simulated in interfacial areas between the two phases. Simulations predicted a gradual shift of PE between 16.9-19.2 eV over a ~5 nm distance due to the interface effect. In addition, a delocalization length of ~16 nm was measured for the 16-20 eV energy-loss window. Results showed that the observed interfacial ribbons stemmed from a combination of the interface effect and the delocalized nature of the plasmon vibration, and not from the formation of interfacial ζ- and γ-ribbons.
In the next step, the formation of the ζ- and γ-phases as bulk precipitates was investigated. Synchrotron X-ray diffraction examination of water-quenched hydrides revealed a diffraction peak at the d-spacing value ~2.70 Å, which can stem from either the (0004)ζ or {111}γ planes. In a quest for the bulk ζ-precipitates, nano-hydrides were characterized in [0001], <112̅6>, <101̅4>, and <112̅0> orientations where NBED patterns identical to those reported for the ζ-phase in previous works were collected. Analysis of electron diffraction patterns revealed that reflections that are conventionally attributed to the ζ-phase, in fact, originate from either the δ-phase covered with a thin surface phase (probably Zr-oxide) or dynamical scattering events between the α-Zr and δ-hydride in overlapped areas. Finally, EELS and NBED detected only the γ- and δ-phases in the microstructure, but not the ζ-phase.
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ProQuest PhD and Master's Theses International Dissemination Agreement
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This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.