Texture Evolution in Zr Grain-refined by Equal Channel Angular Pressing
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Texture Evolution in Zr Grain-refined by Equal Channel Angular Pressing S.H. Yu1, H.S. Ryoo1, D.H. Shin2 and S.K. Hwang1,3 School of Materials Science and Engineering, Inha University, Incheon, Korea, 402-751 2 Department of Metallurgy and Materials Science, Hanyang University, Ansan, Gyunggi-Do, Korea, 425-791 3 Jointly appointed by the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, Korea 1
ABSTRACT To explore a possibility of obtaining an ultra fine grain size in hcp materials, equal channel angular pressing (ECAP) was applied to commercially pure Zr with the initial grain size of 20 µm. To ensure the crack-free specimen during the severe deformation it was necessary to adopt different die designs at the two processing temperatures, room temperature and 350°C. Submicrometer scale grains, in the order of 200 nm, were obtained by employing the die design of 90°/20° and the deformation temperature of 350°C. With the proper choice of the processing parameters, the refined grains were surrounded by the high angle boundaries. During the severe plastic deformation, the crystal texture underwent a significant change, from a fiber texture to that of a strong (0002) component mixed with a medium {10 1 0 } components, suggesting a dual slip mode of deformation on the plane of the maximum shear stress.
INTRODUCTION Zirconium, having a low neutron cross section and a high resistance to corrosion, is an important metal in nuclear energy applications. Many components in the nuclear reactor core are made of Zr, fuel cladding and pressure tubes being examples of the primary utilization of Zr-base alloys. Current Zr-base alloys have been designed on the basis of alloying additions such as Nb and Sn to enhance the structural properties related to nuclear energy generation such as the yield strength and the corrosion resistance. With the recent advances in the ultra-fine grain technologies of bulk metals, however, it is of interest to investigate the possibility of applying this non-conventional strengthening route to Zr, which might prove to be attractive in terms of the long-term economic advantage since the components may become smaller in dimension. In this respect, equal channel angular pressing (ECAP) is considered to be a potential means of achieving improved mechanical as well as the electrochemical properties in this metal. Despite its wide success in metals of cubic crystal structure [1-5], ECAP application in materials of hcp system is relatively scanty except for Mg and Ti. So far there is no report of the related research attempt in Zr. In the present study, we address the possibility of grain refining Zr through a severe plastic deformation process. Along with the grain refinement, the issue of texture has been also addressed in the context of the deformation mechanism since it is another important attribute in the performance of the nuclear core components.
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