Oxidation and creep failure of alloy 617 foils at high temperature

The microstructure of thermally grown oxides (TGO) and the creep properties of alloy 617 were investigated. Oxidation and creep tests were performed on 100 pm thick foils at 800-1000 degrees C in air environment, while the thickness of TGO was monitored in situ. According to energy dispersive X-ray (EDX) mapping micrographs observation, superficial dense oxides, chromia (Cr2O3) which was thermodynamically unstable at 1000 degrees C, and discrete internal oxides, alumina (alpha-Al2O3), were found. Consequently, the weight of the foil specimen decreased due to the spalling and volatilization of the Cr2O3 oxide layer after an initial weight-gaining. Secondary and tertiary creeps were observed at 800 degrees C, while the primary, secondary and tertiary creeps were observed at 1000 degrees C. Dynamic recrystallization occurred at 800 degrees C and 900 degrees C. while partial dynamic recrystallization at 1000 degrees C. The apparent activation energy, Q(app.) for the creep deformation was 271 kJ/mol, which was independent of the applied stress. (C) 2008 Elsevier B.V. All rights reserved.