9508986 Shores Oxide scales that protect alloys during exposure to high temperature oxidizing conditions invariably develop stresses which can be large enough to cause the scale to fracture and spall. Scale origin, magnitude and evolution with time is not well understood, yet mechanical damage to scales is often the principal cause of failure. In this work, scale and substrate strains are measured as a function of time and temperature for two nickel-base alloys. This tests the hypothesis that stress evolution during oxidation is a dynamic balance of stress generation resulting from scale growth and stress relaxation from creep of the metal substrate. The research has several parts: (a) obtain experimental stress history data to evaluate the extent to which substrate creep or scale cracking is responsible for stress relaxation; (b) develop a computer model to account for the evolution of scale stresses in terms of materials properties and scale growth mechanisms, considering especially stress generation during isothermal oxidation and stress relaxation by substrate creep; (c) input to the model experimentally measured stresses and gradients in the scale thickness direction; (d) characterize scale cracking at measured stresses in terms of current theories. %%% This research project is important because of an understanding of the origin of scale stresses. Knowledge of their magnitudes and evolution with time is necessary to characterize scale cracking and spalling. Such an understanding can provide a rational design basis for improving the performance of scales on high temperature alloys. ***
