Modeling of the influence of oxidation on thin-walled specimens of single crystal superalloys

The microstructural evolution of uncoated single crystal superalloys is modeled taking into account the interplay between oxide growth and substrate response. Experimental investigations demonstrate that γ′ fraction of specimens with thicknesses less than 1 mm are strongly affected by oxidation. A model based on thermodynamic and kinetic data only, is presented calculating the growth kinetics of oxide scales and the resulting influence on microstructure evolution of the substrate. The model combines models for oxide growth and substrate response. Currently the main focus is on alumina (A1 ₂O₃) scale growth as it is the most important oxide for long term behavior. A dynamic growth parameter is used to describe the growth rate of the alumina scale. The model predicts the distribution of the alloying elements as well as the evolution of the generated phases as functions of depth and oxidation time. The model has been applied to three different alloys: the strong alumina forming alloy René N5, the moderate alumina forming alloy M247LC SX and the weak alumina forming alloy SCA425+. Since the γ′ fraction is one of the most relevant factors for high temperature creep properties, the present work concentrates on the calculation of the time and space dependent γ′ precipitate profile, which is most important for thin wall specimens. The predictions have been verified with very good agreement at an oxidation temperature of 980°C with respect to alumina scale growth and γ′ fraction distribution. Predicted and measured alumina scale growth and γ′ fraction distribution for oxidation at 980°C are in very good agreement.