Oxidation of Metals, Vol. 49, Nos. 1/2, 1998 Modeling of Residual Stress in Oxide Scales S. J. Bull* Received December 30, 1996; revised April 22, 1997 The magnitude of the residual stress in an oxide scale, and how this varies with temperature, is of major importance in understanding the failure mechan- isms of oxide scales. This stress encompasses both growth stresses introduced at the oxidation temperature and thermal-expansion-mismatch stresses induced on heating and cooling, as well as any externally applied stresses or stress relaxation which takes place in the scale/substrate system. Although some of these components are reasonably well understood (e.g., thermal stresses), growth stresses and the relaxation of the total scale stress by creep or fracture processes are much less well understood. In this study a model has been developed to predict stress generation and relaxation in oxide scales as a function of time and temperature for both isothermal exposure and cooling to room temperature. The model determines growth stress and thermal-stress generation in the scale and how this is balanced by stresses in the substrate. The substrate stresses are then allowed to relax by creep and the scale stresses recalculated. This model accurately predicts the room-temperature scale stresses for a range of scale/alloy systems. The model can be used to show how the scale stress depends on oxidation temperature, cooling rate, substrate, and scale thickness. The model predictions are discussed in light of experimen- tal observations for alumina scales on FeCrAlY. KEY WORDS: oxidation; creep; residual stress; growth stress; thermal stress; alumina scales. INTRODUCTION Failure of oxide scales by spallation, buckling or through-thickness cracking is controlled by the levels of stress in the scale and substrate. 1 However, *Department of Mechanical, Materials and Manufacturing Engineering, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, U.K. 1 0030-770X y 98y0200-00010$15.00 y 0 Ó1998 Plenum Publishing Corporation