Microstructure and Growth Mechanism of Oxide Layers Formed on Zr Alloys Studied with Micro-Beam Synchrotron Radiation

Abstract

The structures of oxides formed in water and lithiated water on three Zr-based alloys with varied corrosion behavior were studied with micro-beam synchrotron radiation and optical microscopy. Micro-beam synchrotron radiation (0.2 µm spot) has a unique combination of high elemental sensitivity (ppm level) and fine spatial resolution that allowed the determination of various oxide characteristics such as phase content, texture, grain size, and composition as a function of distance from the oxide-metal interface. Micro-beam X-ray fluorescence shows that the oxides formed in lithiated water have increased levels of Fe absorbed from the autoclave environment indicating greater oxide porosity in these oxides. The phase content, texture, and grain size of oxides were studied in detail using synchrotron radiation micro-beam diffraction for samples corroded in water and lithiated water. A remarkable periodicity was observed in the oxide structures using various techniques including X-ray peak intensities for both monoclinic and tetragonal zirconia, texture, and optical microscopy. The periods were similar to the transition period and were less visible in the oxides that behaved worse in lithiated water. These results are discussed in terms of models of oxide growth and of the differences between alloys.