Characterization and Simulation of Residual Stress Generation during the Oxidation of Silicon Carbide

Abstract

Oxidation of SiC-containing turbine and other structural components during high temperature operation generates residual stresses that can potentially lead to life-limiting environmentally assisted crack growth and failure. Currently, residual stress generation and/or relaxation during thermal oxidation of SiC is poorly understood. Here a combined experimental-modeling framework is introduced that provides new insight into the mechanisms of oxide formation, and, the magnitudes of the residual stresses induced when SiC is subjected to an oxidizing environment. SiC plates are oxidized at several temperatures over varying time periods, where after laser interferometry is employed to characterize the deformation induced in the plate due to the buildup of residual stress from the formation of the oxide. In this manner, values of the mismatch strain generated upon oxidation are extracted. In parallel, an integrated modeling approach for SiC oxidation is introduced that incorporates the essential physics associated with the diffusion of oxidant and effluent species, reaction at/near the interface, stress generation and viscoelastic/plastic relaxation mechanisms that accompany oxidation, respectively, and their interplay. Results are discussed regarding the generation and evolution of stress as the passive oxide layer grows at different temperatures in the range 500-1000ºC range. Insights obtained on the role of viscoelastic/plastic accommodation in oxidation and residual stress relaxation, and, the mechanisms underlying stress generation, are discussed. The impact of oxidation on environmentally assisted failure of SiC structures is also addressed.