Wrinkling of α-alumina films grown by oxidation -: II.: Oxide separation and failure

Two types of localized separation of the alpha-Al2O3 scale, grown on a Fe-Cr-Al alloy at 1000 degrees C, occur after isothermal oxidation and cooling to room temperature. One type is a form of buckling where the size of the detached region is much larger than the thickness of the oxide and is usually accompanied by substantial stress relaxation and cracking of the scale. Tt is observed within a narrow range of oxide thickness of about 0.2-0.5 mu m. The second type is intimately related to the wrinkling morphology of the scale and takes place primarily along the ridges of the longer wavelength wrinkles. No significant stress relaxation in the oxide appears to accompany this form of separation unless cracking of the scale occurs as well. The consequences of thermal cycling on these modes of separation and how they may lead to oxide spalling are discussed. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.