Modeling W-V and W-Ta Alloys for Fusion Applications: Phase Stability, Short-Range Order and Point Defect Properties
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Modeling W-V and W-Ta Alloys for Fusion Applications: Phase Stability, Short-Range Order and Point Defect Properties M. Muzyk1, D. Nguyen-Manh2, K.J. Kurzydlowski1, N.L. Baluc3 and S.L. Dudarev2 1 Faculty of Materials Science and Engineering, Warsaw University of Technology, 02-507 Warsaw, Poland 2 EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, United Kingdom. 3 Centre de Recherches en Physique des Plasmas, Association EURATOM - Swiss Confederation Ecole Polytechnique Fédérale de Lausanne, ODGA-C110, 5232 Villigen PSI, Switzerland ABSTRACT We have performed density-functional theory (DFT) calculations of phase stability, formation energies of radiation defects in tungsten-based binaries W-Ta and W-V. These alloys are candidate for DEMO divertor applications because of their high melting point and expected improved ductility and fracture toughness in comparison with tungsten. We have identified the lowest energy intermetallic compounds, which should form at low temperatures, and calculated the effective inter-atomic interactions. Using Monte-Carlo calculations, we calculated the temperature of order-disorder phase transformations for these alloys. The predicted temperature of order-disorder phase transformations is relatively low and at high temperature it is found that the short-range order is present for both alloys. Ab-initio calculations also show that vanadium atoms strongly trap self-interstitial atom defects in W-V alloys, whereas Ta atoms in W-Ta alloys have very little effect on either the formation energy or thermally activated mobility of self-interstitial atom defects. INTRODUCTION Tungsten is characterized by an attractive combination of engineering properties mainly because of its high melting temperature, high-temperature strength, good thermal conductivity and low sputter rates, which make it suitable for many high-temperature technological applications including the use of lamp filament manufacture in the lighting industry. Most recently, tungsten is considered as one of important materials in fusion-power plant technology for its use as plasma-facing armor or shield component and structural purposes [1-4]. An armor material needs high crack resistance under extreme thermal operation conditions and compatibility with plasma-wall interaction phenomena [5-6], while a structural material has to be ductile within the operation temperature range. Both material types have also to be stable with respect to high neutron irradiation doses and helium production rates all future (DEMO) designs of fusion devices. The drawbacks of W include its high brittle to ductile transition temperature (BDTT) [7], the significant degree of irradiation embrittlement, which occurs even if the materials is irradiated at a relatively high irradiation temperature, and re-crystallization effects affecting its high-temperature performance [8], which together represent a major scientific challenge for the fusion materials science [9]. In this paper, we choose vanadium (V) and tantalum (Ta) a
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