Crystallographic, Morphological and Kinetic Studies of the Alpha-Beta Transformation in the Niobium-Hydrogen System
Ko, Chul Gi
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https://hdl.handle.net/2142/71857
Description
Title
Crystallographic, Morphological and Kinetic Studies of the Alpha-Beta Transformation in the Niobium-Hydrogen System
Author(s)
Ko, Chul Gi
Issue Date
1988
Doctoral Committee Chair(s)
Wayman, C. Marvin
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Abstract
The group VB bcc metal-hydrogen systems have been extensively studied in the last few years. These studies are relevant to nuclear-reactor technology, superconductivity, and energy storage devices. The elements nitrogen and hydrogen form interstitial solid solutions with the group VB bcc metals and also form a large number of ordered phases. The non-metal atoms occupy a certain set of the possible interstitial sites in these ordered phases and the unit cells of the ordered structure are generally larger than those of the simple metal cells. The ordered phases are found over a wide range of stoichiometry and exhibit many different structures. The niobium-hydrogen system contains an extensive single phase solid solution, a region of spinodal decomposition, and several ordered hydride modifications.
A new type of phase transformation was proposed by Rashid and Scott$\sp{(1)}$ for the VB bcc metal-hydrogen systems. They pointed out that a preferential concentration of hydrogen atoms can occur at stress fields as a result of diffusion, leading to the nucleation of hydride plates at these sites by a shear type mechanism. In recent papers$\sp{(2-5)}$, the crystallography of the formation of $\beta$ vanadium and zirconium hydrides has been compared with the predictions of the phenomenological crystallographic theory of martensitic transformations. These papers suggest the mechanism for the transformation from $\alpha$ vanadium and zirconium to $\beta$ vanadium and zirconium is such that the substitutional atoms undergo a martensitic shear while the hydrogen atoms diffuse to their new ordered positions. To extend the validity of this phenomenological approach, the crystallography and substructure of transformations in niobium hydrides were investigated quantitatively in this work.
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