Determination of the growth stress and strain in α-Al2O3 scales during the oxidation of Fe-22Cr-4.8Al-0.3Y alloy

High temperature oxidation of rectangular plates of Fe-22%Cr-4.8%Al-0.3%Y (wt%) leads to an increase of their size. Measurements of the macroscopic elongational strain and the residual stress in the oxide (by piezospectroscopy) are compared as a function of oxidation time at temperatures 1100, 1200 and 1300 degrees C. Analysis of the experimental results for plates of different initial thickness is used to determine the in-plane growth strain and the concurrent creep strain in the oxide during oxidation. The lateral growth strain in the alpha-Al2O3 scale is found to increase almost parabolically with oxidation time and increase with temperature. It is shown that creep of the oxide provides a significant additional stress relaxation concurrently with the metal lateral expansion. The relative contribution of these two relaxation processes depends on the metal-oxide thickness ratio. (C) 1998 Acta Metallurgica Inc.