Ultrasonic measurement of the kearns texture factors in zircaloy, zirconium, and titanium
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I. INTRODUCTION
THE preferred crystallographic orientation, i.e., texture, developed in ZIRCALOY* during processing, has important *ZIRCALOY is a trademark of Westinghouse Electric Company, Pittsburgh, PA.
effects on the mechanical and physical properties of the material in the resultant components, especially on their anisotropies. For example, nodular corrosion in ZIRCALOY has been shown to be dependent on the texture.[1,2] Studies show that propagation of stress corrosion cracks depends greatly on the orientation of the basal poles.[3] Also important to the nuclear industry is the effect of the texture on the directions of growth of hydride platelets and irradiation strains during service. The texture of sheet and tubing products is greatly influenced by processing variables such as reduction schedule and annealing.[4] Measurement of texture has, to date, been done with X-ray and neutron diffraction. While these diffraction techniques provide good quantification of texture, the methods are, generally, destructive and have limitations. In their usual form, X-ray measurements sense a thin layer exposed to the surface either by virtue of its initial position or machining. Neutron techniques provide volumeaveraged information but require measurements at special facilities. While diffraction techniques employing measurements of multiple pole figures can provide a complete description of texture, industry has found it convenient to use a small subset of this information contained in the Kearns factors.[5] This elementary quantification of texture is based on a weighted average of the information contained
in one pole figure to determine the effective fraction of basal poles aligned along the reference direction. Ultrasonic waves have been used to characterize texture in a variety of material systems, including the cubic metals (steel[6–9] and aluminum[10,11,12]) and the hexagonal metals (titanium, zirconium, and ZIRCALOY[13–16]). Although ultrasonic measurements provide more-limited information than diffraction measurements, there is considerable motivation for their use. In addition to being nondestructive, these ultrasonic techniques are fast, relatively inexpensive, and measure a through-thickness average of the texture, making them attractive alternatives to the currently used X-ray techniques. This article investigates the possibility of using these techniques to predict Kearns factors. The qualitative feasibility of such an approach has been demonstrated by Konishi and Honji,[17] who showed a correlation between the velocity of a longitudinal ultrasonic wave propagating in the normal direction of sheets and tubes and the Kearns factor in the normal direction. However, their explanation used the simplified model of Rosenbaum and Lewis[18] for the effects of texture on velocity. They note that a more-complete description is possible, but was not necessary for their needs. Development of this morecomplete description is one of the objectives of the present article. The authors’ motivations are not only the desir
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