DETERMINATION OF THE GROWTH STRESS AND STRAIN IN ALPHA-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 macr oscopic elongational strain and the residual stress in the oxide (by p iezospectroscopy) are compared as a function of oxidation time at temp eratures 1100, 1200 and 1300 degrees C. Analysis of the experimental r esults for plates of different initial thickness is used to determine the in-plane growth strain and the concurrent creep strain in the oxid e during oxidation. The lateral growth strain in the alpha-Al2O3 scale is found to increase almost parabolically with oxidation time and inc rease 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 p rocesses depends on the metal-oxide thickness ratio. (C) 1998 Acta Met allurgica Inc.