ZrO2-corrosion-layers and their grain boundary networks

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Zr-alloys are used for nuclear fuel cladding in water-cooled reactors. These alloys corrode in contact with their local-environment, e.g. hot water and steam (Féron 2012). Initially oxidation rapidly results in the formation of a zirconium oxide layer that reduces the oxidation rate. The migration of charged species in the oxide layer is largely controlled by the microstructure (Garner et al. 2015, 2017) and grain boundary network of the oxide layer (Gertsman et al. 1997).Initially a non-equilibrium tetragonal phase close to the metal-oxide interface. However as the Oxide layer gains thickness the location of the reaction interface between metal and oxide are further from the surface. The compressive stress in the oxide layer decrease with distance from the metal/oxide interface to eventually be insufficient to stabilise the tetragonal phase. It transforms to monoclinic ZrO2, which is the stable phase at atmospheric pressure and temperature below 1500 K. In this challenging project, we aim at characterizing the behaviour of different grain boundary networks using state-of-the-art meso- to nano-scale characterisation techniques including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. We will experimentally alter Zr-alloys and investigate how this affects the formation and microstructural properties of the resulting Zr-oxide layers. Eventually the experimental data will be used to explore the microstructures using different modelling approaches.References:Féron, D. (2012) Preface. In Nuclear Corrosion Science and Engineering pp. xxvii-xxix. Elsevier.Garner, A., Hu, J., Harte, A., Frankel, P., Grovenor, C., Lozano-Perez, S., and Preuss, M. (2015) The effect of Sn concentration on oxide texture and microstructure formation in zirconium alloys. Acta Materialia, 99, 259-272.Garner, A., Frankel, P., Partezana, J., and Preuss, M. (2017) The effect of substrate texture and oxidation temperature on oxide texture development in zirconium alloys. Journal of Nuclear Materials, 484, 347-356.Gertsman, V.Y., Zhilyaev, A.P., and Szpunar, J.A. (1997) Grain boundary misorientation distributions in monoclinic zirconia. Modelling and Simulation in Materials Science and Engineering, 5, 35-52.