Focussed ion beam sectioning for the 3D characterisation of cracking in oxide scales formed on commercial ZIRLO™ alloys during corrosion in high temperature pressurised water

Using FIB sectioning and reconstruction techniques we have performed a quantitative analysis on the microstructure of cracks and the topography of the metal–oxide interface in oxides formed on ZIRLO™ alloys in high-temperature water. The most significant observation is the continuous production of cracks both before and after the transition in kinetics, not a sudden burst of crack nucleation at transition as assumed in the literature. By concluding that cracks are not generated as a result of the transition and are not the primary cause, we suggest that a process by which cracks within the scale become connected to the oxidising environment through interconnected nanoporosity may be critical in controlling the overall rate of oxidation.

► FIB 3D sectioning has been used for the analysis of cracking in zirconium oxides. ► We observe a gradual production of cracks, not a sudden burst of crack nucleation at transition. ► The location of cracks near the metal/oxide interface is closely linked to the interface geometry. ► Cracks are not generated as a result of the kinetic transition, but may instead play a role in encouraging the transition. ► The process by which cracks become connected to the oxidising environment may be critical controlling the corrosion rate.