EELS and atom probe tomography study of the evolution of the metal/oxide interface during zirconium alloy oxidation

In an effort to understand the mechanisms resulting in the variations of corrosion rate observed throughout corrosion including at the first kinetic transition when the oxide temporarily loses its protective character, the oxide/metal interfaces of autoclave corroded Zircaloy-4 and ZIRLO™ before and after the transition are characterized using electron energy loss spectroscopy and atom probe tomography. The results reveal a complex structure of different phases at different stages of corrosion. The oxide/metal interface exhibits an intermediate layer, with an oxygen content between 45 and 55 O at.% and a suboxide layer corresponding to an oxygen-saturated solid solution in the metal matrix side (∼30 O at.%). Local variations are observed in the width of these characteristic structural features, especially near the transition. Good agreement on the layers present as well as their order, composition, and width was seen with the two techniques.