INFLUENCE OF EPITAXY AND ORDERING ON THE MECHANICAL-BEHAVIOR OF AN OXIDE LAYER ON A METALLIC SUBSTRATE

We have developed a thermomechanical model which allows to study the i nfluence of the metallic ion ordering in a three-dimensional metal-oxi de interface, which is strongly related to the epitaxial relationship. We have shown that a phase transition can lead to a mechanism of low- temperature modification of the interface morphology and duplex struct ure formation. The model is applied to the case of epitaxial systems s uch as (001)Ni//(001)NiO and (111)Ni//(001)NiO. According to the calcu lation, the influence of the epitaxy on the isothermal oxidation growt h regimes is stronger for the scale developed on the (111)Ni surface. The numerical calculation of the growth and the residual stresses in t he metal-oxide system has been performed taking into account the micro structural duplex morphology of the oxide scale and also the growth de formation due to the interfacial ordering that has been detected by LE ED analysis. The variation of the equivalent stress which varies from 0 to 500 MPa during cooling from high oxidation temperature to room te mperature is presented together with the stress profiles. (C) 1998 Els evier Science S.A. All rights reserved.