Oxidation kinetics of some nickel-based superalloy foils and electronic resistance of the oxide scale formed in air Part I

Haynes 230. Inconel 625. Inconel 718. and Hastelloy X foil specimens were oxidized in air for several thousand hours in the temperature range of 800-1100 degrees C. The oxidation kinetics of alloys studied obeyed the parabolic rate law. Haynes 230 exhibited the slowest oxidation kinetics of the alloys studied. X-ray diffraction, scanning electron microscopy, and electron probe microanalysis (EPMA) were the principal characterization tools employed. Chromium oxide, Cr2O3, was the predominant oxide phase in the oxide scale of ail alloys studied. Manganese chromite was also detected in the oxide scales of Haynes 230, Hastelloy X, and Inconel 625. EPMA showed that the concentration of Mn in the oxide scale was much higher than in the alloy, indicating selective oxidation of Mn. The electronic resistance of the oxide scale was measured in air at temperatures up to 800 degrees C on samples oxidized in air for up to several thousand hours. The oxide scale on Haynes 230 exhibited the lowest area-specific resistance, consistent with its slower oxidation kinetics. (C) 1999 The Electrochemical Society. S0013-4651(98)12-100-6. All rights reserved.