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 o xidized in air for several thousand hours in the temperature range of 800-1 100 degrees C. The oxidation kinetics of alloys studied obeyed the paraboli c rate law. Haynes 230 exhibited the slowest oxidation kinetics of the allo ys studied. X-ray diffraction, scanning electron microscopy, and electron p robe microanalysis (EPMA) were the principal characterization tools employe d. Chromium oxide, Cr2O3, was the predominant oxide phase in the oxide scal e 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 co ncentration of Mn in the oxide scale was much higher than in the alloy, ind icating selective oxidation of Mn. The electronic resistance of the oxide s cale was measured in air at temperatures up to 800 degrees C on samples oxi dized in air for up to several thousand hours. The oxide scale on Haynes 23 0 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.