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Uranium-10wt% zirconium (U-10Zr) alloy nuclear fuels have been used for decades and new variations are under consideration ranging from U-5Zr to U-50Zr. As a precursor to understanding the fission gas behavior in U-Zr alloys using ion implantation, a basic study on the U-Zr metallurgy was completed using EPMA, DSC, XRD, Optical microscopy, and TEM with a focus on solid state phase transformations in alloys containing 2, 5, 10, 20, 30, and 50wt% zirconium. Alloys were cast by crucible melting using high temperature furnace under argon atmosphere in yttrium oxide crucibles and various thermal profiles were used to study phase transformations in these alloys. Using TEM, XRD, and DSC data, it was ascertained that athermal-ω, along with martensitic α1, formed in all alloys quenched from γ phase. XRD could detect the presence of athermal-ω only in U-20, 30 and 50wt%Zr alloys. BSE images for as-cast alloys of 2, 5, 10, 20, and 30wt%Zr had lamellar microstructure with lamellae rich in zirconium. All alloy samples clearly showed a heating transformation pertaining to δ → γ in DSC data while XRD could only confirm the presence of δ phase in U-20, 30, and 50wt%Zr alloys. An explanation is offered for the absence of δ phase peaks in uranium-rich alloys based on its formation mechanism. Alloy samples of U-2, 5, and 10wt%Zr were step-cooled from γ phase by annealing in the (α + δ) phase field before cooling to room temperature revealed broad peaks for δ phase indicating incomplete collapse of {111}γ planes. Both as cast and γ- quenched alloys were annealed at 600degreeC, in the (α + δ) phase field for 1, 3, 7, and 30 days. Microstructures of the samples in both cases contained uranium-rich matrix and zirconium-rich precipitates and WDS analyses were consistent with their being α-U and δ phase respectively. However, XRD data for annealed alloys never showed peaks for δ phase even though it’s area fraction was within the detection limits. Moreover, the peaks which were present in U-20wt%Zr vanished after annealing for 7 days. Based on the data obtained, it is suggested that it is more appropriate to consider the presence of metastable diffusional-ω instead of a stable δ in the as-cast alloys and that it is not stable at 600degreeC.

Zircaloy-2 is used extensively in the nuclear industry as a structural material for the reactor core in both light and heavy water reactors. The intergranular strains and texture greatly affect the mechanical properties of the material while in operation. Understanding the plastic deformation of Zircaloy-2 will improve on current plastic deformation models, particularly for twinning mechanisms, which are more active at lower temperatures, and are not yet well understood. For this study, neutron diffraction was used to track the lattice spacing and peak intensity in warm-rolled and recrystallized Zircaloy-2 slab for various crystallographic orientations at 77 K. Tests were performed in all three principle directions under tension and compression. The texture was measured for the deformed samples to help interpret the dominant deformation systems and then Electron Back Scattering Diffraction was used to identify and image the active twinning modes. Prism <a> slip, basal <a> slip, {10-12} and {11-2 1} tensile twinning, and {11-2 2} compression twinning were found to be contributing deformation systems in Zircaloy-2 at 77K. In this study, the diffraction elastic constants for Zircaloy-2 at room temperature and 77K are reported for the first time in open literature. These values will be useful in future experimental work by allowing a conversion between lattice spacing and residual stress. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-09-24 13:41:25.371

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Experimental data on the structural phase changes in zirconia are summarized. The computational techniques of molecular dynamics are reviewed and equations of motion are formulated which allow the study of phase changes as a function of temperature and pressure. The molecular dynamics program NPT which was written for this purpose is described. This program performs numerical integration of the classical equations of motions in atomistic simulations which allow a varying cell size and shape. The simulations produce time averages which are related to thermodynamic ensemble averages. Routines used to calculated the interatomic forces are implemented for potentials which vary as the inverse power of the separation distance between atoms. Calculation of Coulomb forces is done with the Ewald method and with a multipole method. The two methods are shown to be analytically equivalent and the precision and speed of the two routines are compared. Results generated by the program NPT are presented for energy minimization of crystal structures and for dynamic simulations. A number of different minimum-energy structures for soft-sphere potentials are found. Simulations are performed for several soft-sphere structures and dynamic properties are established. Structural phases changes are observed in two cases. A potential derived from ab initio calculations for monoclinic zirconia is tested. / Graduation date: 1994

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 27, 2008) Includes bibliographical references.

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Thadhani, Naresh; Committee Member: Doyoyo, Mulalo; Committee Member: Kecskes, Laszlo; Committee Member: Li, Mo; Committee Member: Sanders, Thomas; Committee Member: Zhou, Min.

Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. Document formatted into pages; contains vii, 69 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 62-64).

Thesis (Master)--İzmir Institute Of Technology, İzmir, 2006. / Keywords: Hydroxiapatites, alumina ceramic, zirconium oxide, urea, precipitations. Includes bibliographical references (leaves. 73-75).