Detection of Breakaway for a High-Temperature Oxidation of Pure Zirconium Using Acoustic Emission Correlated to Thermogravimetry
Résumé
The paper focuses on the phenomenon of breakaway occurring in high-temperature oxidation of zirconium. The oxidation kinetics were determined by thermogravimetric analysis of samples oxidized at 500 °C under synthetic air. The time associated with breakaway was identified and compared to results of an oxidation test coupled with an acoustic emission monitoring. Breakaway corresponded to the appearance of the first cracks in the zirconia scale and which generated an acoustic activity. A significant evolution of bursts energy and an increase in the number of hits allowed to class signals into three populations corresponding to the different steps of the oxidation kinetics. Postmortem observations for qualification of crack networks confirmed crack initiation at the oxide/metal interface at breakaway. A time offset was measured between first cracks occurring and their global effect on oxidation kinetics.