Direct examinations of oxide scales upon cooling: a new way to analyse oxide scale spallation
Résumé
The spallation behaviour of thick alumina scale grown at 1300 degreesC on PM2000 alloy was investigated by recording the events occurring upon cooling from 1300 degreesC down to ambient temperature with CCD cameras. The evolutions of the spalled surface fraction with time and temperature as well as the trajectories of spalled particles were observed and analysed. These observations and analysis were used to determine the critical temperatures drops and incubation times for the onset of spallation as well as to calculate the kinetic energies of spalled oxide particles which is a part of the energy balance describing the interfacial decohesion, the fracture and finally the spallation of oxide scales. In addition to the usual spallation phenomenon resulting in the ejection of small but measurable oxide spalls, localized and sudden outbursts of very fine oxide powders were also observed, showing that oxide scale spallation is likely a phenomenon more complex than usually considered.