WRINKLING OF ALPHA-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 an d cooling to room temperature. One type is a form of buckling where th e 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 al ong the ridges of the longer wavelength wrinkles. No significant stres s relaxation in the oxide appears to accompany this form of separation unless cracking of the scale occurs as well. The consequences of ther mal cycling on these modes of separation and how they may lead to oxid e spalling are discussed. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.