WRINKLING OF ALPHA-ALUMINA FILMS GROWN BY THERMAL-OXIDATION - I - QUANTITATIVE STUDIES ON SINGLE-CRYSTALS OF FE-CR-AL ALLOY

Quantitative measurements of the wrinkling morphology of the alpha-alu mina scales formed by thermal oxidation at 1000 degrees C and its evol ution with oxidation time have been made using atomic force microscopy . The wrinkling wavelength and amplitude, and from these the surface a rea of the scale, for (110), (100) and (111) oriented single crystals of Fe-Cr-Al alloy as a function of oxidation time are presented. The r esidual stress in the scales is determined using piezospectroscopy. To gether these results provide the basis for determining the lateral str ains associated with the growth of the oxide. Crystallographic orienta tion of the alloy surface has a pronounced effect on both the wrinklin g morphology and stress in the scale during the first 20-30 h of oxida tion. The presence of the reactive element, yttrium, suppresses wrinkl ing and restricts lateral growth but it does not decrease the stress i n the oxide. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Sci ence Ltd. All rights reserved.