Microstructure basis of corrosion resistance of model zirconium alloys

'Full text:' Zirconium-based model alloys were fabricated to isolate the effects of various microstructural features such as second phase particle size, type, volume fraction, or solute content on oxide growth. The corrosion of these model alloys in autoclave tests exhibited wide variation in rates and in breakaway behavior. These differences in corrosion kinetics were investigated by studying the differences in the microstructure of oxide layers formed on these model alloys using submicron-beam synchrotron radiation diffraction and fluorescence and cross-sectional transmission electron microscopy. At the oxide metal interface the protective oxides exhibit a highly oriented tetragonal oxide phase and a sub-oxide phase, which are absent in non-protective oxides. In addition, significant differences in the crystallographic texture of protective and non-protective oxides were observed, with the non-protective oxides exhibiting considerably higher anisotropy. These differences between model alloys are rationalized in terms of mechanistic models that relate oxide microstructure with susceptibility to corrosion breakaway. (author)